Dissertations / Theses on the topic 'Anaerobic co-digestion'

Production of biogas through anaerobic digestion is one pathway to achieving the European Union (EU) goals of reducing greenhouse gas emissions, increasing the share of renewable energy, and improving energy efficiency. In this thesis, two different models (Anaerobic Digestion Model No. 1 and an artificial neural network) are used to simulate a full-scale co-digester in order to evaluate the feasibility of such models. This thesis also includes models of two systems to study the inclusion of microalgae in biogas plants and wastewater treatment plants. One of the studies is a life-cycle assessment in which replacement of the ley crop with microalgae is evaluated. The other study concerns the inclusion of microalgae in case studies of biological treatment in three wastewater treatment plants. Finally, the co-digestion between microalgae and sewage sludge has been simulated to evaluate the effect on biogas and methane yield. The results showed that Anaerobic Digestion Model No.1 and the artificial neural network are suitable for replicating the dynamics of a full-scale co-digestion plant. For the tested period, the artificial neural network showed a better fit for biogas and methane content than the Anaerobic Digestion Model No. 1. Simulations showed that co-digestion with microalgae tended to reduce biomethane production. However, this depended on the species and biodegradability of the microalgae. The results also showed that inclusion of microalgae could decrease carbon dioxide emissions in both types of plants and decrease the energy demand of the studied wastewater treatment plants. The extent of the decrease in the wastewater treatment plants depended on surface volume. In the biogas plant, the inclusion of microalgae led to a lower net energy ratio for the methane compared to when using ley crop silage. Both studies show that microalgae cultivation is best suited for use in summer in the northern climate.

The meat sector is one of the most important industrial sectors in Europe and it is associated with the generation of large quantities of animal by-products not intended for human consumption (ABPs). The increasing demand of renewable energy sources and reuse of wastes require good technological solutions for energy production such as anaerobic digestion (AD), which is included in the current European regulation as one of the allowed methods to valorize ABPs. Due to their composition, with high fat and protein content, ABPs can be considered good substrates for the AD process, according to the high potential methane yield. Although, slow hydrolysis rates and inhibitory process have been reported, with a suitable pre-treatment to improve particulate materials solubility and/or co-digestion process of several complementary materials the anaerobic digestion can be improved. Hence, the aim of this thesis was to evaluate the feasibility of different ABPs for anaerobic digestion. Emphasis was placed on the effect of pre-treatments on the organic matter, methane yield and methane production rate. Within this scope, thermal (pasteurization and sterilization) and high pressure pre-treatments (200, 400 and 600 MPa) were applied. Thermogravimetric and spectroscopy techniques (DTG-MS and FTIR), where used to determine the effects on the organic matter. The effects on the methane yield and methane production rates, including the disintegration parameters, were obtained by means of batch test with different inoculum to substrate ratios (ISR). The suitability of ABP for anaerobic digestion was confirmed with samples from different origin (poultry and piggery slaughterhouses) but the results showed that methane yield depends on the substrate composition (amount of proteins, fats and carbohydrates), especially when a thermal pre-treatment is applied. The thermal pre-treatment produced some inhibitory nitrogen-related compounds when there was a high carbohydrate and protein concentration and also affected the methane potential rate. On the other hand, thermal pre-treatments (pasteurization and sterilization) increased the methane production rate and methane production yield in the case of a waste with high protein and fat concentration. The results of the disintegration kinetics determination underline these positive effects on the methane production rate being increased in the after pasteurization. The high pressure pre-treatments were tested with piggery ABP without obtaining any effect on the methane production or methane production rate. The study and optimization of the co-digestion of pasteurized ABP with pig slurry was reported, including the glycerin addition. It showed to be feasible and glycerin addition resulted in an improvement of the methane production. Changes in the microbial composition were followed by means of denaturing gradient gel electrophoresis (DGGE) and it was demonstrated that the microbial community of the Eubacteria domain was more sensitive to operational changes than the Archaea domain. In conclusion, this study contributes to the understanding of the anaerobic process of ABP mainly related to the effect of the thermal pre-treatments and the optimization of the co-digestion process.
El sector cárnico lleva asociada la generación de grandes cantidades de subproductos animales no destinados al consumo humano (SANDACH). La demanda de fuentes de energía renovables y la reutilización de los residuos requieren soluciones tecnológicas tales como la digestión anaerobia (DA), proceso incluido en el reglamento europeo actual como uno de los métodos permitidos para valorizar estos subproductos. Debido a su composición rica en grasa y proteína, los SANDACH son considerados buenos sustratos para la DA, dado su elevado rendimiento teórico de producción de metano, aunque se han notificado tasas de hidrólisis lentas y procesos inhibitorios. Con un pretratamiento adecuado, que mejore la solubilidad de los materiales particulados, y/o un proceso de codigestión con residuos complementarios, la DA se podría mejorar. El objetivo de la presente tesis es evaluar la viabilidad de diferentes SANDACH para la DA, centrándose principalmente en el efecto de los pretratamientos sobre la materia orgánica, el rendimiento y la tasa de producción de metano. Para ello se emplearon pretratamientos térmicos (pasteurización y esterilización) y de altas presiones (200, 400 y 600 MPa). Posteriormente, se utilizaron técnicas termogravimétricas y de espectroscopía (DTG-MS y FTIR), además de una caracterización clásica, para determinar los efectos sobre la materia orgánica, mientras que los efectos sobre la producción de metano, incluyendo los parámetros de desintegración, se obtuvieron por medio de ensayos discontinuos con diferentes ratios inoculo/sustrato. La idoneidad de los SANDACH para la DA fue confirmada con residuos de mataderos avícola y porcino, pero los resultados mostraron que el rendimiento de metano dependía de la composición relativa (proteínas, grasas e hidratos de carbono) de cada sustrato, especialmente en el caso de los pretratamientos térmicos. Se observó que cuando el residuo contenía una elevada concentración de hidratos de carbono y proteínas, se generaban compuestos nitrogenados recalcitrantes durante el pretratamiento térmico que afectaban negativamente a la tasa de producción de metano. Por el contrario, cuando el residuo tenía una concentración elevada de proteína y grasa, tanto la tasa de producción como el rendimiento de metano aumentaron tras la pasteurización y esterilización. Estos resultados fueron confirmados mediante el estudio de la cinética de desintegración. En último lugar, el pretratamiento a altas presiones, aplicadas a residuo de matadero de cerdo, no modificó la biodegradabilidad ni el rendimiento de metano del residuo. En paralelo, se estudió la codigestión en continuo de SANDACH pasteurizado con purín porcino y glicerina, optimizándose la producción de biogás mediante el control de la composición de la mezcla de residuos a tratar. Se observaron cambios en las poblaciones microbianas (monitorizados mediante DGGE) y se comprobó que las eubacterias fueron la comunidad dominante, aunque también más sensible a los cambios operacionales que las arqueas. En conclusión, la producción de biogás a partir de SANDACH se ha mostrado factible, mejorando su DA mediante codigestión con otros residuos que permitan equilibrar su composición y un pretratamiento térmico, siendo la eficacia de este muy dependiente de la composición en proteínas e hidratos de carbono.

Anaerobic digestion is a key energy and resource recovery technology. This work investigated potential organic waste resources to co-digest with household food waste (HFW) to stabilise the process and future-proof feedstock availability. This included novel feedstock macroalgae (seaweed) waste (SW). Hydrothermal (autoclave) pretreatment was also investigated to optimise energy recovery from HFW and SW. Preliminary experiments investigated the behaviour of HFW co-digested with either a green waste (GW) or paper waste (PW), using a batch-test laboratory scale and systematic approach with a revised waste mixture preparation method. Following preliminary trials, the co-digestion of HFW/SW was investigated using an air-dried SW mixture. Batch experiments to determine the biomethane potential (BMP) at different ratios of HFW to SW were set up. Co-digesting HFW and SW at ratio 90:10 (d.w.) achieved a BMP similar to HFW alone (252±13 and 251±1 cm3 g-1 VS, respectively), and a peak methane yield for HFW:SW (90:10) at day 12 of 69±3% compared to a peak methane yield for HFW at day 19 of 70±3%. Addition of SW optimised the C/N ratio, increased concentrations of essential micronutrients and produced an overall increase in reaction kinetics. Concentrations of SW ≥25%, associated with high sulphur levels, reduced final methane productivity. Analysis of the macroalgae strains L. digitata, U. lactuca and F. serratus from the SW mixture was carried out to compare mono-digestion and co-digestion with HFW at a 90:10 ratio and the effect of autoclave pretreatment at 136°C. Co-digestion had a positive impact on methane yields for U. lactuca and F. serratus, whilst autoclave pretreatment had no significant impact on the SW strains When results were modelled for a 320 m3 anaerobic digester treating 8m3 feed per day the theoretical energy balance showed that optimal energy production from pretreated HFW at 8.09 GJ/day respectively could be achieved. To verify the suitability of using macroalgae, known to readily uptake polycyclic aromatic hydrocarbons (PAH), toxicity tests were used to determine the impact of phenanthrene sorbed by U. lactuca on the AD process. Despite U. lactuca’s ability to biosorb phenanthrene in under 2 hours, no impact on the AD process was observed. Overall, results of this study demonstrated that co-digestion of HFW and SW, at batch laboratory scale, provide a viable and sustainable waste revalorisation solution. In addition, low temperature autoclave pretreatment increased methane production (p=0.002) from the AD of HFW.

Wastewater treatment plants (WWTPs) are characterized by their high organic matter and nutrient removal efficiency, but also by their high energy consumption. In the current context where resources are increasingly scarce, all feasible strategies to save energy emerge as an important issue for the sustainable management of WWTPs. In this thesis, sewage sludge (SS) anaerobic co-digestion with available organic wastes, coming from different sources and having different compositions, was proposed as an interesting strategy to approach an energy self-sufficient scenario for wastewater treatment by means of an improved biogas production. The studied co-digestion strategies were focused on the effect of the co-substrates composition -lipids, by adding grease waste (GW) from the dissolved air unit of the WWTP; alcohols, by adding crude glycerol (CGY) from a biodiesel facility; and of mixed composition, when adding the organic fraction of municipal solid waste (OFMSW)- and the effect of operational temperatures mesophilic and thermophilics on the general performance of the SS anaerobic digesters. This approach was evaluated in terms of methane yield and the stability of the process. Methane productivity increased 2.3 and 2.2 times in comparison with sewage sludge mono-digestion when the GW added amounted to 26% and 27% of the COD inlet under mesophilic and thermophilic temperature conditions, respectively. The addition of GGY showed a 2.5 increase in methane productivity under mesophilic temperature, while in thermophilic range the co-digestion showed great instability mainly due to volatile fatty acids accumulation. Addition of the OFMSW showed a 3 to 5 times increase in methane productivity compared to SS mono-digestion, when the OFMSW added amounted respectively to 51% and 33% of the COD inlet under mesophilic and thermophilic conditions respectively. The biomass acclimatization brought about by a slow increase of the influent dose of GW, could be a good strategy to increase fat degradation and reduce the inhibitory effect of LCFAs. Thermophilic co-digestion showed a lesser tolerance to LCFAs than mesophilic, and therefore, the adaptation time to grease waste was longer. Thermophilic anaerobic co-digestion of SS with CGY proved to be very unstable due to the extreme pH of CGY and its fast decomposition into volatile fatty acids. On the other hand, mesophilic co-digestion showed a good performance, concluding that doses above 2% v/v of CGY did not bring about an improvement on the methane yield. In this case, it can be concluded that the optimization strategy based on the C/N ratio must be modulated by other factors such as the characteristics of crude glycerol (particularly its pH and total alkalinity) and the operational temperature. The OFMSW was proved to be a suitable co-substrate both under mesophilic and thermophilic temperature conditions. Results suggest that the addition of the OFMSW could be an adequate strategy to promote the activity of thermophilic saturated fatty acid oxidizers and acetoclastics methanogenic bacteria. In addition, the evolution of specific activities was assessed and used as a feasible tool to explain and manage the response of the system, especially when conventional control parameters were not enough to explain the performance of the reactor. Within the obtained results, it has been demonstrated that co-digestion is a suitable approach to optimize the energy balance of a WWTP. But, depending on the composition of the organic waste and the temperature range of operation, different operational strategies should be put into practice to find the most stable process, and avoid inhibitory episodes. Based on the results obtained with the strategies studied in this PhD thesis, sewage sludge co-digestion with different organic wastes could be expected to represent an attractive alternative to attain energy self-sufficient wastewater treatment operations, and perhaps even net energy producing WWTPs
Les Estacions de Depuració d’Aigües Residuals (EDARs) es caracteritzen per la seva elevada eficiència en l’eliminació de la matèria orgànica i nutrients, però també per el seu elevat consum energètic. En aquesta tesis, la co-digestió anaeròbia de fangs d'EDAR amb residus orgànics de diferent orígens i composicions, s'ha proposat com una estratègia atractiva per apropar-se a un escenari de tractament d'aigües residuals autosostenible energèticament, per mitjà de la millora de la producció de biogàs. L’estudi de l'estratègia de co-digestió es va centrar en l'efecte de la composició dels co-substrats (lípids mitjançant l'adició de residus greixosos procedents de la unitat de flotació per aire dissolt -DAF- de l’EDAR, alcohols mitjançant l'adició de glicerina crua d'una industria de producció de biodièsel, i una composició mixta aportada per la fracció orgànica de residus municipals -FORM-), i l'efecte de la temperatura d'operació (mesòfil i termòfil) en el rendiment general del procés de digestió anaeròbia dels fangs d'EDAR. La producció de metà es va incrementar entre 2,3 i 2,2 vegades en comparació amb la mono-digestió dels fangs d'EDAR quan l'adició del residu greixós representava el 26% i el 27% de la DQO d’entrada, durant la digestió mesòfila i termòfila respectivament. L'adició de la glicerina crua va mostrar un increment en la producció de metà de 2,5 vegades durant la digestió mesòfila, mentre que el procés de co-digestió en condicions termòfiles va mostrar una elevada inestabilitat, principalment deguda a l’acumulació d’àcids grassos volàtils. L'adició de FORM va incrementar la producció de metà entre 3 i 5 vegades més que la mono-digestió dels fangs d'EDAR, quan l'adició de FORM va ser del 51% i el 33% de la DQO d'entrada, a temperatures de operació mesòfiles i termòfiles respectivament. L'adaptació de la biomassa mitjançant increments lents de la dosis del residu greixós, es va demostrar com una bona estratègia per incrementar la degradació dels lípids i reduir l'efecte inhibitori dels àcids greixosos de cadena llarga. La co-digestió termòfila va mostrar una menor tolerància als àcids greixosos de cadena llarga que la digestió mesòfila, i per tant, el temps d¿ adaptació de la biomassa termòfila va ser superior. La co-digestió anaeròbia termòfila dels fangs amb la glicerina crua va mostrar una gran inestabilitat degut al pH extrem que presentava la glicerina i la seva ràpida descomposició en àcids grassos volàtils. Per un altra banda, la co-digestió mesòfila va mostrar un bon rendiment, concloent que dosis addicionals de glicerina per damunt de 2% v/v no mostraren una millora en el rendiment de metà. L'estratègia d'optimització basada en la relació C/N cal que sigui modulada per altres factors com les característiques de la glicerina crua (especialment el pH i l’alcalinitat total) i la temperatura d'operació. La FORM es va mostrar com un co-substrat adequat per a treballar tant a rangs de temperatures mesòfiles com termòfiles. Els resultats obtinguts suggereixen que l'adició de la FORM podria ser una estratègia vàlida per fomentar l'activitat de les poblacions termòfiles oxidats d’àcids grassos saturats, i les poblacions metanogèniques acetoclàstiques. Així mateix, l'evolució de les activitats específiques es va avaluar com una eina viable per explicar i gestionar les respostes del sistema, especialment quan els paràmetres de control convencionals no van mostrar-se adequats per explicar el rendiment del reactor. Els resultats obtinguts han demostrat que la co-digestió es un bon enfocament per optimitzar el balanç energètic del les EDARs. Basant-se en els resultats obtinguts amb les estratègies de co-digestió de fangs d'EDAR estudiades en esta PhD tesis, s'espera que la co-digestió dels fangs amb diferents residus orgànics, representen una alternativa atractiva per aconseguir l’autosuficiència energètica de les EDARs, i fins i tot, que les EDARs es converteixin en instal·lacions productores netes d'energia.

Microalgae-based wastewater treatment systems are promising solutions to shift the paradigm from wastewater treatment to energy and resources recovery. In these systems, microalgae assimilate nutrients and produce oxygen which is used by bacteria to biodegrade organic matter improving water quality. Moreover, microalgae biomass can be harvested and reused to produce biofuels among other bioproducts. In this context, anaerobic digestion (AD) is one of the most consolidated and well-known technologies to convert organic waste generated in a wastewater treatment plant into bioenergy. However, microalgae AD is generally limited by their resistant cell wall, which lead to low methane potential (degradation extent) and conversion rate (degradation speed). Also, microalgae have high protein content, which can lead to ammonia nitrogen inhibition during the anaerobic digestion process. This PhD thesis aims to overcome these drawbacks and improve the technology by combining the use of pretreatments and the co-digestion. While pretreatments act disrupting or weakening the structure of microalgae cell wall, allowing the intracellular content to become more bioavailable, anaerobic co-digestion (i.e. the simultaneous digestion with two or more substrates) can contribute to improve microalgae AD performance by increasing methane potential, diluting inhibitory compounds or getting synergies between substrates (nutrients composition, rheology, etc.) in addition to the economic advantages derived from treating several wastes in a single facility. Firstly, co-digestion of harvested microalgae from high rate algal ponds (HRAP) used as secondary treatment for urban wastewater and primary sludge, which is produced in the same treatment process, is been investigated. Results have shown that the most suitable option to anaerobically digest microalgae from HRAPs would be the co-digestion with primary sludge at a 20-day hydraulic retention time (HRT), that leads to higher methane production (between 63% and 2.3-fold increase). The energy assessments conducted according to these results have revealed that microalgae co-digestion with primary sludge is a key technology for energy recovery in HRAPs, since the energy produced is up to 4-fold the energy consumed during the AD. Finally, potential reuse of microalgae digestates in agriculture has been investigated (including their co-digestion with primary sludge). all microalgae digestates have presented suitable properties for agricultural soils amendment, although digestate from co-digestion has presented the least phytotoxicity. Besides, co-digestion with storable agricultural wastes (i.e. wheat straw) is been evaluated. As it happens to microalgae, wheat straw AD is limited by hydrolysis step due to its lignocellulosic structure. Thus, their co-digestion with microalgae is also being investigated after a simultaneous thermo-alkaline pretreatment to both substrates. Results have shown that wheat straw co-digestion (50% VS) at 20-day HRT has increased microalgae methane yield by 77% as compared to microalgae mono-digestion (from 0.12 L CH4/g VS to 0.21 L CH4/gVS). On the other way around, pretreatment has only increased the methane yield by 15% as compared to untreated substrates co- digestion (0.24 L CH4/g VS). Thus, the co-digestion of microalgae and wheat straw is successful even without the pretreatment. Finally, when microalgae are used as tertiary treatment, waste activated sludge (WAS) results in abundant and available co-substrate. As a novelty, in this PhD thesis, microalgae and WAS co-digestion is investigated after applying a simultaneous autohydrolysis pretreatment at 55 °C to improve microalgae biodegradability by promoting inherent enzymes release from WAS. However, results have shown that WAS enzymes have not been effective at disrupting microalgae cell wall. Anyway, WAS co-digestion (80% VS) after pretreatment has increased microalgae mono-digestion methane yield up to 130%.
Els sistemes de tractament d'aigües residuals amb microalgues són solucions tecnològiques que permeten canviar el paradigma del tractament d'aigües residuals a la recuperació d'energia i recursos. En aquests sistemes, les microalgues assimilen nutrients i produeixen oxigen que utilitzen els bacteris per a la biodegradació de matèria orgànica, millorant així la qualitat de l'aigua. A més, la biomassa de microalgues es pot recol·lectar i reutilitzar per produir biocombustibles. En aquest context, la digestió anaeròbia és una de les tecnologies més establertes que permeten convertir els residus orgànics generats en una depuradora en bioenergia. No obstant això, la digestió anaeròbia de microalgues està generalment limitada per la seva resistent paret cel·lular, i per aquest motiu presenten un baix potencial de metà i una Baixa taxa de degradació (velocitat de degradació). A més, les microalgues tenen un elevat contingut en proteïnes, fet que pot conduir a la inhibició per amoníac durant el procés de digestió anaeròbia. Aquesta tesi doctoral pretén millorar la tecnologia de la digestió anaeròbica combinant l’aplicació de pretractaments amb la co-digestió. Mentre que els pretractaments actuen per alterar o debilitar l'estructura de la paret cel·lular de les microalgues, permetent que el contingut intracel·lular sigui biodisponible, la co-digestió (és a dir, la digestió simultània amb dos o més substrats) pot contribuir a millorar el rendiment de la digestió de les microalgues augmentant el potencial de metà, diluint compostos inhibidors o fomentant sinergies entre substrats (composició de nutrients, reologia, etc.), a més dels avantatges econòmics derivats del tractament de diversos residus en una única instal·lació. En primer lloc, s'ha investigat la co-digestió de les microalgues procedents de llacunes d’alta càrrega (LLAC), utilitzades com a tractament secundari per a aigües residuals urbanes, i fangs primaris, que es produeixen en el mateix procés de tractament. Els resultats obtinguts indiquen que l'opció més adequada per digerir microalgues és amb la codigestió amb fang primari en un temps de retenció hidràulica (TRH) de 20 dies. Els balanços energètics duts a terme d'acord amb aquests resultats han mostrat que l'energia produïda és fins a 4 vegades l'energia consumida durant la digestió anaeròbica. Finalment, s'ha investigat la possible reutilització dels efluents de la digestió de microalgues en l'agricultura (inclosa la seva co-digestió amb fang primari). Tots els digestats de microalgues han presentat propietats adequades per se utilitzats com esmena de sòls agrícoles, tot i que l’efluent procedent de la codigestió ha presentat la menor fitotoxicitat. Complementàriament, s'ha avaluat la codigestió amb residus agrícoles que puguin ser emmagatzemables (palla de blat). Com passa amb les microalgues, la digestió anaeròbia de palla de blat està limitada per hidròlisi a causa de la seva estructura lignocel·lulosica. Per tant, la seva codigestió ambles microalgues també s'ha investigant després d'un pretractament simultani a tots dos substrats (termoalcalí). Quan les microalgues s'han co-digerit amb palla de blat, el rendiment del metà ha augmentat des de 0,12 L CH4 / g VS fins a 0,21 L CH4 / gVS (augment del 77%), mentre que el pretractament només ha augmentat el rendiment del metà en un 15% en comparació amb la codigestió dels substrats no tractats (0,24 L CH4 / g VS). Per últim, s’ha investigat la codigestió de microalgues i fangs biològics després d'aplicar un pretractament simultani a ambdós substrats d'autohidròlisi (55 °C). L’objectiu d’aquesta estratègia és millorar la biodegradabilitat de les microalgues per mitjà de l'alliberament d'enzims inherents als fangs. Tot i que en els assajos s’ha vist que els enzims alliberats pels fangs no han estat eficaços degradant la paret cel·lular de les microalgues, la codigestió amb els fangs biològics després del pretractament ha permès permet augmentar la producció de metà de les microalgues fins a un 130%.

Energy shortfall and air pollution are some of the challenges the human kind is facing today. Fossil fuel is still the most widely used fuel, which is a non-renewable resource, increasing excess carbon dioxide into the air. To overcome these issues, and reduce the carbon footprint, a greater development of renewable energy from green and natural resources is required. Compared to fossil energy, renewable energy has the benefit to reduce greenhouse gas emissions. There are different solutions available for green and renewable energy. Biomass is all biologically produced matter. Through the biological breakdown of biomass, biogas can be produced through the process called anaerobic digestion. This work was focused on the production of biogas, using algal biomass, sewage sludge and coffee grounds in an anaerobic co-digestion system. The main goal of this study was to investigate the feasibility of combining these three substrates. Two different types of algae were employed; Chlorella vulgaris and Scenedesmus sp. and the investigations included even the cultivation and harvesting of algal biomass. The production of biogas was examined under anaerobic conditions using 5 batch reactors in duplicate under constant temperature of 37 °C in 30 days. The result showed that co-digestion of algal biomass with sewage sludge led to an enhanced biogas production by 75 % compared to that of just sewage sludge. This indicates the synergistic effects of co-digestion. However, the addition of coffee ground to the mixture lowered the biogas production. All mixtures except the two with coffee grounds were in neutral pH. Methanogens, involved in the last step in biogas production are very sensitive to pH, and pH around 7 is the optimal for their activity. Furthermore, the presence of caffeine in the coffee ground could also inhibit the biogas production.

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior
Microalgae, microscopic life forms with photosynthetic capacity, produce oxygen thanks to light energy. Due to this capacity, microalgae are used for sewage treatment in stabilization ponds, however, this activity generates a large amount of microalgal biomass. In view of this excess of biomass production and its disposal in water bodies produces unpleasant effects, it has been evaluated the re-use of this biomass as a substrate for methane production in anaerobic digestion. Since microalgae have a rigid cell wall, the application of microalgae hydrolysis tests was necessary in order to improve its biodegradability. Heat pretreatment for 30 minutes at 120ÂC and 1 kgf/cm2 resulted in the best pretreatment applied. In order to improve C/N ratio, residual glycerol coming from biodiesel production was used to perform co-digestion with microalgae. Residual glycerol coming from biodiesel production (1Kg of glycerol per 10 Kg of biodiesel generated) is an impure residue which is also produced at large scale as a byproduct from the trans-esterification of fats and oils. In fact, the presence of impurities limits its applications. In this study, different COD/N ratios of 20 (phase 2), 40 (phase 3) and 70 (phase 4) were tested and the organic loading rate (OLR) applied ranged from 0,06 to 0,75 kg/m3.d. In the phase 1 only microalgae was used on the influent. Two modified UASB reactors were used. One of them was fed with pretreated microalgae, while the other one was fed with non-pretreated microalgae. Both of them were operated in co-digestion with glycerol. COD removal efficiencies ranged between 40% and 90%. Biogas produced presented values of 73% and 84% for each bioreactor treating pretreated and non-pretreated microalgae, respectively. Neither nitrogen nor ammonia and total and volatile suspended solids was significantly removed. Moreover, microalgae were the sole source of macro and micro-nutrients in this work. Sodium bicarbonate was used as a buffer during the phase 4, since pH fall down enough to harm the anaerobic digestion process at the beginning of phase 4. Based on the maintenance of adequate VFA/Alk ratios, both reactors presented a stable operation, specially the reactors treating pre-treated microalgae. Instability periods were mainly observed in some operation phases in the reactor without pretreatment. Specific methanogenic activity tests were carried out in order to evaluate the quality of the inoculum in terms of activity and methane production. Methane production presented a mean value of 0,26 g DQO-CH4/g SSV.d.
As microalgas, seres microscÃpicos com capacidade fotossintÃtica, produzem oxigÃnio na presenÃa de energia luminosa. Devido a isso as microalgas sÃo utilizadas para tratamento de esgotos em lagoas de estabilizaÃÃo, porÃm essa atividade gera uma grande quantidade de biomassa algal. Tendo em vista a produÃÃo dessa biomassa e sua destinaÃÃo em corpos hÃdricos provocando efeitos desagradÃveis, buscou-se avaliar a reutilizaÃÃo dessa biomassa como substrato para produÃÃo de metano a partir da digestÃo anaerÃbia. Devido à presenÃa de uma parede celular rÃgida, verificou-se a necessidade da aplicaÃÃo de testes de hidrÃlise para as microalgas com a finalidade de melhorar sua biodegradabilidade, sendo observado o melhor prÃ-tratamento aplicado, o tÃrmico por 30 minutos a 120ÂC e 1 kgf/cm2. Para melhorar a relaÃÃo C/N, utilizou-se o glicerol residual do biodiesel para realizaÃÃo de co-digestÃo com microalgas. O glicerol residual do biodiesel (1 kg de glicerol para cada 10 kg de biodiesel produzido), alÃm de ser um resÃduo impuro, à tambÃm produzido em grande escala como subproduto da transesterificaÃÃo de Ãleos e gorduras e sem muitas aplicaÃÃes devido exatamente a presenÃa de impurezas. Foram testadas relaÃÃes DQO/N de 20 (fase 2), 40 (fase 3) e 70 (fase 4), alÃm da relaÃÃo apenas das microalgas (fase 1), sendo as COV aplicadas, variando de 0,06 a 0,75 kg/m3.d. Foram utilizados dois reatores semelhantes ao UASB (UASB modificado), nos quais continham microalgas brutas e prÃ-tratadas, ambos em co-digestÃo com o glicerol. As remoÃÃes de DQO variaram de 40 a 90%. O biogÃs produzido teve rendimentos de atà 73% para o reator degradando microalgas prÃ-tratadas e 84% para o reator degradando microalgas brutas. NÃo houve remoÃÃes significativas de amÃnia e sÃlidos suspensos totais e volÃteis, tambÃm nÃo foram utilizados macro e micronutrientes, sendo esses nutrientes fornecidos apenas pelas microalgas. O bicarbonato de sÃdio como tampÃo foi utilizado apenas na Ãltima fase (fase 4), devido a queda do pH para uma faixa nÃo aceitÃvel para digestÃo anaerÃbia, no inÃcio dessa fase. As condiÃÃes de estabilidade foram mantidas, baseadas na relaÃÃo AGV/Alc, que se manteve em faixas aceitÃveis, principalmente para o reator operando microalgas prÃ-tratadas, sendo observado valores indicativos de instabilidade em algumas fases no reator sem prÃ-tratamento. Foi realizado teste de atividade metanogÃnica especÃfica para avaliar o lodo de inÃculo quanto a atividade e produÃÃo de metano, obtendo-se valor mÃdio de 0,26 g DQO-CH4/g SSV.d.

Nitrogen Inhibition during an anaerobic co-digestion process was studied in this work.The substrate and inoculum used were obtained from a thermophilic biogas plant Sobacken,situated in Borås, Sweden. The batch experiments have been carried out in triplicate reactorswith different concentrations of ammonia ranging from 2400mg/l to 3400mg/l. The batchexperiment was working well for the all the concentrations of ammonia investigated. Theaverage methane yield was around 0.65 Nm3 CH4/kgVS for all the reactors. The laboratorywork has been further proceeded with a continuous process having two reactors working inparallel. Reactor 1 containing only substrate and the Reactor 2 contain substrate with surplusammonia added to make final concentration of 3400mg/l. The reactors were operated atorganic loading rate (OLR) of 3.3gVS/l/day and hydraulic retention time (HRT) of 20 days.Both reactors worked well for 29 days. During a period of an initial stable operation, theaverage methane production of Reactor 1 was 0.59 Nm3CH4/kgVS/day and for Reactor 2 theproduction rate was 0.56 Nm3CH4/kgVS/day. Then Reactor 1 showed a steady decrease in pHand methane production, while Reactor 2 showed stable operation for a few days longer withdecreasing pH and methane production only from day 36. The composition of substrate wasnot optimal; therefore the inhibition level of ammonium could not be determined.

The Brazilian sugarcane and ethanol industries produce lot of waste which has potential for energy production. Anaerobic digestion (AD) can be effectively utilized for producing biogas from these wastes. During the AD process, huge volumes of digestate are produced with some being employed in fertilizer application whilst large volumes are mostly stored in uncovered tanks. This result in emission of residual methane and loss of energy which can be recovered through post- digestion approaches. To analyse optimal utilization of this digestate and enhanced biogas production, co- digestion of post- digestate from a continuously stirred reactor (CSTR) performing co-digestion of sugarcane waste from Brazil (Vinasse, filter cake and straw) with addition of different glycerol concentrations were studied. The addition of glycerol characterised by its biodegradability and high organic content makes it a suitable substrate to enhance biogas production. A biomethane potential was assessed when the digestate was co-digested with 15% and 25% CODg/L of glycerol. The batch test lasted for 39 days. The results demonstrated that, co-digestion of digestate with glycerol has the potential of increasing cumulative methane and biogas yield with 25% addition producing the highest methane and biogas yield (318 Nml/gCOD and 196 Nml/gCOD) which was approximately 6 times higher compared to mono-digestion of the digestate. Anaerobic co-digestion of digestate and glycerol was examined in two lab scale reactors (CSTR) at mesophilic conditions (35oC) and were run for 90 days. The reactor (R1) performing co-digestion increased methane and biogas production by 300% and 170% when glycerol concentrations of 15% and 25% of influent COD were added, respectively. Moreover, there was a decrease in CH4 yield when the reactors were continuously fed with 15% and 25% CODg/L of glycerol. This was an indication that, microorganisms easily digested glycerol addition at the early stages. Glycerol addition (50% CODg/L) resulted in a decrease in CH4 and biogas production.  This result shows, CH4 yields in the post-digester can be enhanced with glycerol addition if it does not exceed a limiting of 50% of the organic loading rates of the feed.

Microalgae harvested from wastewater treatment ponds can be anaerobically digested to produce biogas, a renewable fuel resource. However, past experiments have shown some limitations of algae digestion. Algal cell walls are thought to be resistant to digestion, and the high protein content of algae can lead to ammonia toxicity in digesters. Co-digestion of algae with substrates containing higher C:N ratios (e.g., waste paper) can be used to maintain non-inhibitory ammonia concentrations and increase methane production. However, high carbon waste co-substrates have become costly or are not readily available in many communities. Although domestic wastewater sludge has only a marginally higher C:N ratio than algae biomass, sludge is a practical co-substrate for treatment pond facilities using primary sedimentation. The present laboratory research evaluated the use of wastewater sludge as a co-substrate with treatment pond algae that were harvested by coagulation and dissolved air flotation. The research was meant to assist in the planning for full-scale algae digestion at a large pond facility in California. The independent variables evaluated were algae/sludge ratio in the digester feed (100% to 0%), organic loading rate (OLR; 2 or 4 g volatile solids/L-d), and hydraulic residence time (HRT; 20 or 40 d), while the main dependent variables were methane yield, volumetric methane production, and the dewaterability of the digester effluents. Co-digestion of algae with sludge was stable, with healthy pH, at all algae/sludge ratios with OLRs up to 4 g volatile solids loaded per liter digester per day (g VS/L-d) at a 20-d HRT. For digesters fed algae biomass exclusively, at a 2 g VS/L-d OLR and a 20-d HRT, the methane yield was 0.26 L/g VS-d and methane productivity was 0.52 g VS/L digester-d. A control digester fed sludge exclusively, with the same loading rate, produced more methane: the yield was 0.44 L/g VS-d and production was 0.87 L/L-d. No significant synergistic benefit in algae methane yield was observed due to co-digestion with wastewater sludge. The effluent from digesters fed only algae dewatered as effectively or better than digesters fed only wastewater sludge. However, freezing of the algae biomass prior to digestion could have affected the results. An engineering model was developed to estimate heating requirements and net electricity production for full-scale algae digesters. For two example climates (Mediterranean and continental desert), the model predicted that despite the lower methane production of algae digestion, heat recovered from cogeneration and electricity generation would be more than sufficient to fulfill the inputs required for algae digestion. For facultative pond wastewater treatment facilities with existing collection and digestion of primary sludge, addition of the algae produced to the digesters is expected to increase electricity production by 120%.

This research sought to optimize anaerobic co-digestion of microalgae biomass harvested from a wastewater treatment pond facility with locally-available wastes. The goal was to produce high methane yields and stable digestion without the need for supplemental alkalinity addition. A key research question was if algae digestion could be improved via the synergistic effects of co-digestion. Cell disruption to increase digestibility was not pursued due to its relatively high mechanical complexity and high energy use. For the wastewater treatment ponds studied, the most practical co-substrates identified were municipal wastewater sludge and food waste (sorted organic municipal waste). Although wastewater sludge does not have a particularly high carbon:nitrogen (C:N) ratio, it readily and stably digests and is available in large quantities at wastewater treatment plants. This research investigated the methane productivity of algae co-digestion with municipal wastewater sludge and food waste in semi-continuous bench-scale anaerobic digesters at 37.5˚C. Digesters fed pure algae biomass loaded at a rate of 4 g Volatile Solids (VS)/L-day with a 20-day residence time exhibited stable digestion and yielded an average of 0.23 L CH4/g VS Introduced. For digesters that contained algae biomass in the feed, the greatest methane yield of 0.40 mL CH4/g VSin was observed in a digester containing 50% algae co-digested with both sorted organic municipal waste (40%), and municipal wastewater sludge (10%) at a loading rate of 2 g VS/L-day with a 20-day residence time. While adding co-substrates increased yields in all digesters, prevention of ammonia toxicity did not appear to be the mechanism. Instead, the co-substrates simply increased the concentration of readily-digestible organic carbon, leading to increased methane yields and productivities. For algae biomass, total ammonia nitrogen concentrations of 3370 mg/L did not appear to inhibit methane yield. Digesters with the same feed contents and residence time loaded at 2 and 4 g VS/L-d had similar yields but total ammonia nitrogen concentrations of 1740 and 3370 mg/L respectively. From the data from these laboratory studies, descriptive models were developed for ammonia nitrogen, alkalinity, volatile fatty acids, yield, biogas quality, and volatile solids destruction. The variables from the descriptive models with p-values above 0.05 were then used to create a compact model.

Biogas is a source of renewable energy and is produced at anaerobic conditions. The gas consists mainly of methane (55-70 %) and carbon dioxide (30-45 %). Biogas can be used as vehicle fuel after the gas has been upgraded to a methane content of approximately 97 %. There are several companies in Sweden producing biogas. Svensk biogas AB in Linköping is one of the largest. The company has two biogas production plants; one in Linköping and one in Norrköping. To meet the surge demand for biogas it is not only important to increase the volumetric capacity of the digesters, but also to optimize the process at the existing production plants in different ways. Zeolites, a clay mineral, have earlier been shown to have a positive effect on anaerobic digestion of certain substrates. The aim of this master’s thesis was to investigate if the organic loading rate could be increased and/or if the hydraulic retention time could be reduced by addition of zeolites to a reactor treating slaughterhouse waste as a substrate. The aim was further to investigate which substance/substances that zeolites possibly could affect. Addition of the zeolite clinoptilolite in a continuously stirred lab tank reactor showed a significantly lower accumulation of volatile fatty acids compared to that in a control reactor without zeolites added, when the hydraulic retention time was kept low (30 days) and the organic loading rate was high (4.8 kg VS/ (m3 × day)). The same results were observed upon zeolite addition in a batch experiment, which also showed a decreased lag phase. Neither the specific gas production nor the methane concentration was significantly affected by addition of zeolites. Furthermore, addition of a possible inhibitor, long-chain fatty acids (LCFA), increased the lag phase further when slaughterhouse waste was used as a substrate. The conclusion from the observed results is that a metabolite or metabolites produced during the anaerobic degradation is/are the reason to inhibition and an increased lag phase.

The main objective of this study was to investigate the removal and recovery of nutrients from anaerobic digestion residues of poultry manure through struvite (MgNH4PO4.6H2O, MAP) precipitation. To this purpose, three sets of laboratory experiments were conducted. In the first set, separate and co-digestion of poultry manure and sewage sludge were studied in laboratory-scale mesophilic anaerobic batch reactors and subsequent struvite precipitation experiments were conducted with the reactors effluents. The effects of important parameters on struvite precipitation were investigated and it is illustrated that up to 89 % of NH4-N, 84 % PO4-P and 42 % COD removals were possible. In the second set, the effluents of a full-scale co-digestion plant utilizing poultry manure and maize silage were subjected to struvite precipitation experiments. Acidic phosphorus-dissolution process was successfully applied to the solid phase effluents to obtain phosphorus-enriched solution. By the addition of external Mg and P more than 90% of NH4-N and PO4-P were recovered from phosphorus-enriched solution, whereas the addition of only Mg led to partial recovery of NH4-N. In the third set, the effluents of a full-scale poultry manure digester were subjected to struvite precipitation experiments. The findings illustrated that Ca has inhibitory effects on the struvite reaction and lead to formation of hydroxlyapatite and amorphous calcium phosphates together with struvite. Based on the results obtained in this study, it is postulated that, struvite precipitation is a viable option for the recovery of the nutrients in the anaerobically digested poultry manure. This study illustrated that, poultry manure, if managed properly, could meet one-fourth of Turkey&
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s domestic fertilizer demand.

This research investigates an alternative approach to the use of two wastes from agricultural and livestock activities developed in Colombia. Swinemanure and coffee mucilage were used to evaluatean anaerobic co-digestion process focused on hydrogen production. In addition, the aims covered a further stage in order to close the cycle of the both wastes. The thesis was conducted in three phases : 1. Evaluation of hydrogen production from the co-digestion of coffee mucilage and swine manure during dark fermentation ; 2. Trends over retention time through the monitoring of microorganisms by quantitative PCR and other parameters incluiding pH, oxidation reduction potential, and hydrogen partial pressure ; 3. Treatment of the effluent from hydrogen production process by anaerobic digestion with methane production. The experimental results showed that mixtures of both wastes are able to produce hydrogen. A substrate ratio of 5:5, which was associated with a C/N ratio of 53, was suitable for hydrogen production. Moreover, the stability and optimization of the process were evaluated by increasing the influent organic load rate. This wasthe best experimental condition in terms of average cumulative hydrogen volume, production rate and yield which were 2661 NmL, 760 NmLH2/Lwd and 43 NmL H2/gCOD, respectively. This performance was preserved over time, which was verified through the repetitive batch cultivation during 43 days. Two trends were identified over retention time associated with similar cumulative hydrogen, but with differences in lag-phase time and hydrogen production rate. T.thermosaccharolyticum was the dominating genus during the short trend related to the shortest lag phase time and highest hydrogen production rate. The long trends were associated with a decrease of Bacillus sp. concentration at the beginning of the experiments and with the possible competition for soluble substrates between T.thermosaccharolyticum and Clostridium sp. The third phase showed that the use of a second stage to produce methane was useful enhancing the treatment of both wastes. Finally, the overall energy produced for both biofuels (Hydrogen andmethane) showed similar levels with other process. However, hydrogen was around the 10% of the overall energy produced in the process. In addition, both gases could be mixed to produce biohythane which improves the properties of biogas.

Scum is an integral component of solids management in MWWTP and is composed of fats, oils, grease and other entrained floatable materials that are collected during primary clarification. Lab scale BMP tests showed the addition of 14.5 g VS/L of scum exhibited the greatest increase in biogas production of 1.6 times per g VS added compared to the control, while a higher additional scum loading of 33.7 g VS/L reduced the biogas yield to 32% of the control reactor. Lab scale semi-continuous digestion measured the effects of scum loading and temperature of pretreatment in the scum concentrator. At 15 d and 20 d HRTs the greatest observed improvement in biogas was achieved by adding 3% scum by volume and pretreating the scum at 70°C in a scum concentrator with respective improvements of 24% and 16%.

Several operational and environmental conditions can result in poor biogas yield during the operation of anaerobic digesters and anaerobic bioreactor landfills. Over time, anaerobic co-digestion and leachate blending have been identified as strategies that can help address some of these challenges to improve biogas production. While co-digestion entails the co-treatment of multiple substrates, leachate blending involves combination of mature and young landfill leachate. Despite the benefits attributed to these strategies, their impact on recirculating bioreactor landfill scenarios and anaerobic digesters requires further investigation. In the first phase of this thesis, an attempt to assess biogas production improvement from organic fraction of municipal solid waste in simulated bioreactor landfills through recirculation of blended landfill leachate was conducted. Real old and new leachate blends (67%New leachate:33%Old leachate, 33%New leachate:67%Old leachate) as well as 100%New and 100%Old leachate were recirculated through six laboratory-scale bioreactors using open-loop and closed-loops modes. Compared with the control bioreactor where 100% new leachate was recirculated and operated as a closed-loop, cumulative biogas production was improved by as much as 77 to 193% when a leachate blend of 33%New:67%Old was recirculated. Furthermore, comparison of the results from open-loop and closed-loop operated bioreactors indicated that there was approximately 28 to 65% more biogas in open-loop bioreactors. The Gompertz model applied to the methane data produced a better fit (R2 > 0.99) than first order and logistic function models. Leachate blending reduced the lag phase by almost half and thus helps in alleviating the ensiling during the start-up phase. In the second phase, a biochemical methane potential (BMP) assay was conducted to investigate the synergistic effect of percentage sewage scum addition; 10%, 20% and 40% (volatile solids basis) on biogas production during mesophilic co-digestion with various organic substrates viz; organic fraction of municipal solid waste, old leachate, new leachate and a leachate blend prepared from 67%old leachate and 33%new leachate under sub-optimal condition. Results show that the net cumulative bio-methane yield was improved with increased sewage scum percentage during co-digestion because of positive synergism. Meanwhile, the addition of 40% sewage scum to the individual co-substrates improved net cumulative bio-methane yield by 28% - 67% when compared to their respective mono-substrate digestion bio-methane yield. Furthermore, reactors containing leachate blends consistently produced more biogas over other sets because of blending. Kinetic modelling applied to the bio-methane production data shows modified Gompertz equation achieved a better fit with up to an R2 value of 0.999. Finally, co-digestion substantially reduced the lag time encountered during mono-digestion. In the last phase, the biomethane potential involved in the ACo-D of sewage scum, organic fraction of municipal solid waste was investigated in this phase using either thickened waste activated sludge or leachate blend (67%old leachate and 33%new leachate) as a tertiary component. Compared to the mono-digestion of TWAS, results shows that biomethane yield was enhanced in by as much as 32 - 127% in trinary mixtures with SS and OFMSW mainly due to the effect of positive synergism. Furthermore, LB addition improved biomethane production in trinary mixtures of SS:LB: OFMSW by 38% than in corresponding trinary mixtures of TWAS. Whereas an optimal combination of 40%SS:10%TWAS:50%OFMSW and 20%SS:70%LB:10%OFMSW produced the highest biogas yield of 407mL.gVS-1 and 487mL.gVS-1 respectively. The application of the first order model showed that lower hydrolysis rates promoted methanogenesis with k = 0.04day-1 in both 20%SS:70%LB:10%OFMSW and 20%SS:50%LB:30%OFMSW. Estimations by the modified Gompertz and logistic function were conclusive methane production rate improved by as much a 60% in a trinary mixture over the production rate during mono-digestion of TWAS alone. The results of the various experiments of this thesis therefore suggest that leachate blending can be used as a strategy to improve biogas production in both bioreactor landfills and anaerobic digesters. Also, sewage scum as an energy-rich substrate can be better utilized during co-digestion with other low-energy substrates.

Anaerobic co-digestion of organic fraction of municipal solid waste (OFMSW), with thickened waste activated sludge (TWAS) and primary sludge (PS) has the potential to enhance (biodegradation) of solid waste, increase longevity of existing landfills and lead to more sustainable development by improving waste to energy production. This study reports on mesophilic batch anaerobic biological methane potential (BMP) assays carried out with different concentrations and combinations (ratios) of OFMSW, TWAS (microwave (MW) pre-treated and untreated) and PS to assess digester stability and potential improved specific biodegradability and potential increased specific biogas production by digestion of OFMSW with PS and TWAS in various tri-substrate mixtures. Results indicated improvements in specific biogas production with concomitant improvements in COD and volatile solid (VS) removal for co-digestion of OMSW, TWAS and PS vs. controls. In terms of improvements in biogas production and digester stability the OFMSW:TWAS:PS:50:25:25 ratio with or without TWAS MW treatment was deemed best for further continuous digester studies. At a 15d HRT which is the regulatory policy in the province of Ontario for municipal mesophilic anaerobic TWAS:PS treatment, co-digestion of OFMSW:TWAS:PS, and OFMSW:TWASMW:PS resulted in a 1.38 and 1.46 fold relative improvement in biogas production and concomitant waste stabilization when compared to TWAS:PS and TWASMW:PS digestion at the same HRT and volumetric VS loading rate respectively. Treatment of OFMSW with PS and TWAS provides beneficial effects that could be exploited at MWWTP that are being operated at loading rates less than design capacity.

Two different sludge pretreatments were investigated in an attempt to improve the management and performance of processes for the co-digestion of biosolids with fats, oils, and grease (FOG). The mechanisms of long chain fatty acids (LCFA) degradation in thermal hydrolysis pretreatment and the influence of pH on LCFA degradation in two-phase co-digestion systems were studied. LCFA thermal hydrolysis was investigated at different temperatures (90-250 °C) and reaction times (30 minutes and 8 hours). Approximately 1% of saturated fatty acids were degraded to shorter chain fatty acids at 140 and 160 °C (8-hr thermal hydrolysis). Only 1% or less of unsaturated fatty acids were degraded from 90 to 160 °C (8-hr thermal hydrolysis). Little degradation (< 1%) of both saturated and unsaturated LCFAs was observed at a 30-min reaction time. Both groups of LCFAs were stable up to 250 °C (30-min hydrolysis). The use of chemical-thermal treatments was also investigated. Only unsaturated LCFAs, C18:1 and C18:2, were degraded when thermally hydrolyzed with hydrogen peroxide coupled with activated carbon or copper sulfate. Semi-continuous, acid-phase digesters (APDs) under different pH conditions were studied in order to understand the effects of pH on FOG degradation. Increases in soluble chemical oxygen demand (SCOD) were observed in all APDs. However, the APDs with pH adjustment appeared to perform better than the controls in terms of solubilizing organic compounds. Approximately 38% and 29% of total COD (TCOD) was solubilized, and maximum volatile fatty acid (VFA) concentrations of 10,700 and 7,500 mg/L TCOD were achieved at pH 6 and 7, respectively; It is useful to note that the feed sludge had a VFA concentration of 2,700 mg/L COD. Higher pH (6.0-7.0) showed less accumulation of LCFA materials and more soluble LCFAs in the APDs. This indicates that the lower pH in the APDs was most likely the cause of precipitation and accumulation of LCFAs due to saturation of unsaturated LCFAs.
Master of Science

La digestion anaérobie représente un des acteurs majeurs du développement durable et de l'économie circulaire dans le concept « des déchets à l'énergie ». Compte-tenu de la grande diversité des déchets organiques, son développement passe par l'optimisation de la co-digestion. D’où la nécessité de développer des outils simples pour caractériser les substrats et pour prédire les performances des digesteurs afin d'optimiser leur fonctionnement. Cette thèse porte sur la caractérisation de la biodégradation des substrats solides par digestion anaérobie et l'optimisation de leur co-digestion à l'aide d'une approche de modélisation simple. En premier lieu, un nouveau protocole pour la quantification du potentiel méthane en mode batch a été mis en œuvre, intégrant une phase d'acclimatation entre l’inoculum et le substrat. Ensuite, un modèle simple a été développé sur la base du fractionnement de la matière organique en trois sous-fractions. Cette approche a permis de développer une base de données incluant les cinétiques et les potentiels en méthane (BMP) de 50 substrats. En second lieu, des expériences de co-digestion de deux substrats solides ont été menées en mode semi-continu à une charge appliquée (cva) constante puis à des charges appliquées croissantes. Les rendements expérimentaux en méthane ont toujours été supérieurs aux valeurs des BMP des mélanges calculées à partir des BMP de chaque substrat, soulignant l'importance de la respiration endogène. Quatre modèles incluant la respiration endogène avec des hypothèses différentes ont été proposés et évaluées pour prédire la production de méthane brute de digesteurs semi-continus en utilisant les données des substrats (BMP et cinétiques) acquises en mode batch. Deux modèles pour lesquels la production expérimentale de méthane à des cva croissantes correspondait bien aux données modélisées ont été validés. L'approche de modélisation retenue a été ensuite appliquée à des mélanges plus complexes de 3 et 5 substrats ainsi qu’à des biodéchets. Enfin, la réponse d’un digesteur fonctionnant en mode de production flexible, c’est-à-dire recevant des surcharges organiques ponctuelles régulièrement a été également modélisée avec succès. L'approche de modélisation proposée fournit un outil simple, pouvant être utilisé par les bureaux d'études, les constructeurs et les exploitants d’unités de méthanisation pour l'optimisation des mélanges de co-digestion et de la cva à utiliser en mode continu. Cela doit permettre de réduire le risque de défaillance et d’optimiser la rentabilité des unités de co-digestion
Anaerobic digestion represents one of the major actors of sustainable development and the circular economy in the concept of "Waste to Energy". Given the great diversity of organic waste, its development requires the optimisation of co-digestion. Hence, it is needed to develop simple tools to characterize substrates and predict digester performance in order to optimize their operation. This thesis focuses on the characterization of biodegradation of solid substrates by anaerobic digestion and optimization of co-digestion using a simple modelling approach. First, a new batch protocol was implemented to quantify the Biochemical Methane Potential (BMP), integrating an acclimatization phase between the inoculum and the substrate. Then, a simple model was developed based on the fractionation of organic matter into three sub-fractions. This approach has allowed to develop a database including kinetics and BMPs of 50 substrates. Second, co-digestion experiments of two solid substrates were conducted in semi-continuous mode at a constant organic loading rate (OLR) and then at increasing applied loads. The experimental methane yields were always higher than the BMP values of the mixtures calculated from the BMPs of each substrate, underlining the importance of endogenous respiration. Four models including endogenous respiration with different assumptions were proposed and evaluated to predict raw methane production from semi-continuous digesters using substrate data (BMP and kinetics) acquired in batch mode. Two models for which the experimental methane production at increasing OLR corresponded well to the modelled data were validated. The chosen modelling approach was then applied to more complex mixtures of 3 and 5 substrates and to bio-waste. Finally, the response of a digester operated in flexible production mode, i.e. receiving regular punctual organic overloads, was also successfully modelled. The proposed modelling approach provides a simple tool that can be useful to design offices, manufacturers and operators of co-digestion units for the optimisation of feed mixtures and OLR to be used in continuous mode. This should reduce the risk of failure and optimise the profitability of co-digestion units

Anaerobic digestion is a sustainable and economically feasible waste management technology, which lowers the emission of greenhouse gases (GHGs), decreases the soil and water pollution, and reduces the dependence on fossil fuels. The present thesis investigates the anaerobic digestion of waste from food-processing industries, including citrus wastes (CWs) from juice processing and chicken feather from poultry slaughterhouses. Juice processing industries generate 15–25 million tons of citrus wastes every year. Utilization of CWs is not yet resolved, since drying or incineration processes are costly, due to the high moisture content; and biological processes are hindered by its peel oil content, primarily the D-limonene. Anaerobic digestion of untreated CWs consequently results in process failure because of the inhibiting effect of the produced and accumulated VFAs. The current thesis involves the development of a steam explosion pretreatment step. The methane yield increased by 426 % to 0.537 Nm3/kg VS by employing the steam explosion treatment at 150 °C for 20 min, which opened up the compact structure of the CWs and removed 94 % of the D-limonene. The developed process enables a production of 104 m3 methane and 8.4 L limonene from one ton of fresh CWs. Poultry slaughterhouses generate a significant amount of feather every year. Feathers are basically composed of keratin, an extremely strong and resistible structural protein. Methane yield from feather is low, around 0.18 Nm3/kg VS, which corresponds to only one third of the theoretical yield. In the present study, chemical, enzymatic and biological pretreatment methods were investigated to improve the biogas yield of feather waste. Chemical pretreatment with Ca(OH)2 under relatively mild conditions (0.1 g Ca(OH)2/g TSfeather, 100 °C, 30 min) improved the methane yield to 0.40 Nm3/kg VS, corresponding to 80 % of the theoretical yield. However, prior to digestion, the calcium needs to be removed. Enzymatic pretreatment with an alkaline endopeptidase, Savinase®, also increased the methane yield up to 0.40 Nm3/kg VS. Direct enzyme addition to the digester was tested and proved successful, making this process economically more feasible, since no additional pretreatment step is needed. For biological pretreatment, a recombinant Bacillus megaterium strain holding a high keratinase activity was developed. The new strain was able to degrade the feather keratin which resulted in an increase in the methane yield by 122 % during the following anaerobic digestion.

Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 1 juni 2012, klockan 10.00 i KA-salen, Kemigården 4, Göteborg.

Biogas production from organic materials can be used as a renewable vehicle fuel, provide heat and generate electricity and can thereby reduce the greenhouse gas emissions. This thesis focuses on the biogas production based on lignocelluloses. There is an abundant availability of lignocelluloses, constituting 50% of the total biomass worldwide. However, the biomass recalcitrance limits the microbial degradation as well as the biogas production from these types of materials. In the present work different pretreatment methods have been performed in order to decrease the biomass recalcitrance and improve the biogas production. Steam explosion pretreatment, together with the addition of sodium hydroxide and hydrogen peroxide, has been performed on lignocellulosic-rich paper tube residuals. The pretreatment has resulted in methane yields of up to 493 NmL/gVS, which is an increase by 107% compared with untreated material. Furthermore, the use of an organic solvent, N-methylmorpholine-N-oxide (NMMO), was evaluated as a pretreatment method for spruce (both chips and milled), rice straw, and triticale straw. The NMMO pretreatment resulted in 202, 395, 328, and 362 NmL CH4/g carbohydrates produced of these substrates, respectively, corresponding to an increase of between 400-1,200% compared with the untreated version of the same material. Moreover, the paper tube residuals have been co-digested with an unstable nitrogen-rich substrate mixture, mainly based on municipal solid waste. The addition of the lignocellulosic-rich paper tubes in a co-digestion process showed stabilizing effects and prevented the accumulation of volatile fatty acids with a subsequent reactor failure. Additionally, synergistic effects have been found leading to between 15-33% higher methane yields when paper tubes were added to the co-digestion process compared with the yields calculated from the methane potentials of the two substrates. Substrate characterization analysis can be used to study the changes on the lignocellulosic components after the pretreatment, relating the changes to the performance in the anaerobic digestion. Increased accessible surface area, measured by the Simons’ stain and the enzymatic adsorption methods, as well as decreased crystallinity, determined by using the Fourier Transform Infrared Spectroscopy, can all be linked to improved biogas production after pretreatment. Finally, the NMMO pretreatment on forest residues has been financially evaluated for an industrial scale process design. The base case that was evaluated simulated a case where pretreated forest residues were co-digested with the organic fraction of municipal solid waste to obtain optimal nutritional balance for the anaerobic digestion. This process has been found to be economically feasible with an internal rate of return of 20.7%.

Akademisk avhandling som för avläggande av teknologie doktorsexamen vid Chalmers tekniska högskola försvaras vid offentlig disputation den 24 maj 2013, klockan 10.00 i KA,Kemigården 4, Göteborg

The Western Dairy Center at Utah State University had recognized through traiing of cheesemaking that a challenge that can exist for farmstead and artisan cheese manufacturing operations is disposal or utilization of the whey that is produced when milk is converted into cheese. Land application of whey is limited and can cause odor problems which would be detrimental to a cheesemaking operation located at the rual-urban interface. The project provided information in support of a research grant from the Western Sustainable Agribulture Research and Education program that was investigating economics and feasiblity of using anaerobic digestion for treatment of whey and cow manure mixtures. We performed initial trials to determine the level of whey that could be mixed with manure and have satisfactory operation of the digester to produce methane and a biomass. A continuous digester was used to produce biomass material for microbiological and physical testing for its suitability for use as a renewable potting mix or soil conditioner. The benefits from this research are that we have shown how a value-added product can be made by converting whey and manure into a deodorized biomass that could replace the use of peat moss, which is a non-renewable resource. This can improve the economics of using a bioreactor for whey disposal.

The study was aimed to investigate the effect of corn stalk pre-treatment duration on biogas production when cow dung and corn stalk was co-digested in an anaerobic digestion. Corn stalks were pre-treated in different durations: 2-days, 5-days, and 8-days before being added to cow dung into anaerobic co-digesters. The experiments were set up randomly by using triplicate batch anaerobic apparatus in 21 L containers that run in 60-days. The mixing ratio between a corn stalk and cow dung was 50%: 50% (based on the volatile solid value of each material), but corn stalk was cut into small pieces with around 10 cm length, while the cow dung was air dried. The results of the study indicated that all operation parameters such as temperature, pH, and alkalinity in the anaerobic batch were suitable for biogas production. The results showed that there was a significant improvement in total gas produced in the pre-treated 5-days treatment (206.4±8.4 L) compared to 2-days (153.4±9.6 L), and 8-days ones (174±11.1 L). The biogas yield of the pretreated 2-days, 5-days, and 8-days treatments were 392.7±9.8 L/kg VSfermented, 469.8±10.1 L/kg VSfermented and 497.1±13.3 L/kg VSfermented, respectively, that was not significantly different (5%). In all treatments, low concentration of methane in the beginning phase had been observed but increased and reached the optimum value for energy use after 10 days. The result of the study showed that it is preferable to have 5-days pre-treatment of corn stalk before the corn stalk is loaded to an anaerobic digester in combination with cow dung.
Nghiên cứu này nhằm đánh giá ảnh hưởng của thời gian xử lý thân cây bắp lên năng suất sinh khí khi ủ phối trộn phân bò và thân cây bắp trong điều kiện yếm khí. Ba mức thời gian xử lý thân cây bắp được chọn là 2 ngày, 5 ngày, và 8 ngày. Các thí nghiệm được bố trí ngẫu nhiên trong các bình ủ yếm khí theo mẻ 21 L, vận hành trong 60 ngày liên tiếp và có 3 lần lặp lại. Nguyên liệu ủ được phối trộn theo tỷ lệ 50% phân bò và 50% thân bắp, trong đó thân bắp được cắt nhỏ cỡ 10 cm. Kết quả thí nghiệm cho thấy tất cả các thông số pH, nhiệt độ, độ kiềm của mẻ ủ đều phù hợp để vận hành. Lượng khí sinh ra của các nghiệm thức xử lý ở 2 ngày, 5 ngày, 8 ngày được ghi nhận là 153,4±9,6 L, 206,4±8,4 L và 174±11,1 L; năng suất sinh khí của các nghiệm thức không khác biệt và đạt giá trị 392,7±9,8 L/kg VSphânhủy, 469,8±10,1 L/kg VSphânhủy và 497,1±13,3 L/kg VSphânhủy. Tất cả các nghiệm thức đều sản sinh lượng CH4 thấp ở giai đoạn đầu nhưng tăng dần theo thời gian ủ và đạt hiệu quả sử dụng sau 10 ngày ủ. Kết quả cho thấy có thể chọn mốc thời gian 5 ngày để xử lý thân cây bắp trước khi đưa vào hầm ủ biogas.

Algae that are grown in wastewater treatment lagoons could be an important substrate for biofuel production; however, the low C/N ratio of algae is not conducive to anaerobic digestion of algae with economically attractive methane production rates. Increasing the C/N ratio in anaerobic, laboratory scale, batch reactors by blending algal biomass with sodium acetate resulted i increased methane production rates as the C/N ratio increased. The highest amount of methane was produced when the C/N was 21/1. When the C/N was 24/1, the biogas production rate decreased. Batch experiments were done to evaluate the effect of optimizing the C/N ratio on methane production from algae and to identify the most essential information needed to conduct research on co-digestion of algal biomass using the continuous, high-rate, up-flow anaerobic sludge blanket (UASB) reactor system. Based on the results obtained from batch reactor experiments, anaerobic co-digestion of algal biomass, obtained by continuous centrifugation from the Logan City, Utah, 5th stage wastewater treatment lagoon, and sodium acetate was conducted using laboratory scale UASB reactors with the C/N ratio in the feedstock adjusted to 21/1. Duplicate, 34 L UASB reactor systems were built of poly(methyl methacrylate). Both reactors were seeded with 11 L of anaerobic sediment from the 3rd stage lagoon. The pH of the feedstock was adjusted to the neutral range. The feedstock was initially introduced at a low organic loading rate of 0.9 g/L.d with a hydraulic retention time (HRT) of 7.2 days and then increased up to 5.4 g/L.d and a HRT of 5.5 days. These organic loading rates corresponded to an initial influent chemical oxygen demand (COD) of 6.25 g/L and increased to 27.2 g/L. Methane production increased from 270 mL/g to 349 mL/g COD biodegraded. COD removal efficiency was 80% and biogas methane composition was 90% at steady state. Algal biomass contributed 33-50% of the COD in the feed stock depending on the COD of the algae paste from centrifugation. The shortest HRT at which steady state was not affected was 5.5 days. At lower HRT all monitored parameters showed a slight decrease after the 75th day of operation.

Tesis por compendio
[ES] Actualmente, la sostenibilidad del sector porcino depende de su capacidad para responder a la elevada demanda de productos ganaderos derivada del crecimiento de la población, adaptándose a los cambios en los contextos económico y político, y mejorando su rendimiento medioambiental mediante la mitigación de su impacto ambiental. En este contexto, el uso de subproductos agroindustriales ofrece materias primas alternativas en producción animal, con una menor carga ambiental asociada, en forma de piensos para el ganado, fuente de compuestos bioactivos o materias primas útiles en la producción de bioenergía. Esta tesis doctoral pretende evaluar el uso de subproductos agroindustriales mediterráneos como ingredientes en piensos para el ganado porcino o como co-substratos para la producción de biogás. Con este objetivo, se diseñaron y realizaron cuatro ensayos para evaluar el uso de subproductos de la industria del aceite de oliva y del zumo de naranja en alimentación porcina, evaluando su valor nutricional y las consecuencias de su inclusión sobre el rendimiento y la salud de los animales, la calidad del producto final y las emisiones de gases de los purines. Además, se realizó un ensayo para evaluar el efecto de cuatro sustratos agrícolas sobre el potencial bioquímico de metano (BMP) en co-digestión anaerobia con purines. Los resultados obtenidos a partir de los ensayos de valor nutricional indican que las tortas de aceituna y las pulpas de naranja ensayadas pueden ser incluidas en la dieta con cambios asociados en la excreción de nutrientes que conducen a modificaciones en las emisiones potenciales de amoníaco y BMP de los purines. En cuanto a los subproductos de la torta de aceituna, el ensayo de valor nutricional con tortas de aceituna crudas (COC) y parcialmente desgrasadas (PDOC) mostró que ambas tortas son fuentes apreciables de fibra insoluble, pero tienen un valor energético limitado (11.2 y 7.4 MJ/kg MS para COC y PDOC respectivamente) y un bajo valor como fuente de proteínas. En cambio, las pulpas de naranja deshidratadas (DOP) y ensilada secada al sol (ESDOP) ensayadas son una fuente de energía relevante (14.2 y 13.2 MJ/kg MS para DOP y ESDOP respectivamente) con valor añadido debido a su contenido en fibra soluble. En los ensayos de emisiones in vitro, los subproductos ensayados generaron una disminución en la excreción de N en la orina y, en el caso de la pulpa de aceituna, un aumento de la excreción de materia seca en heces. La emisión de amoniaco por kg de purín disminuyó con la inclusión de torta de aceituna y pulpa de naranja, mientras que el BMP por animal y día se vio negativamente afectado por la inclusión de torta de aceituna obteniendo un mayor BMP con estos subproductos. En cuanto a los ensayos de rendimientos productivos, la PDOC y la DOP pueden incluirse en la dieta hasta 120 y 240 g/kg respectivamente, sin efectos negativos en el caso de la PDOC y efectos menores para la DOP sobre los rendimientos productivos, la composición corporal y la calidad de la canal. La inclusión de PDOC y DOP no afectó a los recuentos microbianos ni al volumen, la composición y la emisión global de gases de los purines. Además, se observaron efectos beneficiosos sobre la grasa subcutánea con la inclusión de PDOC, mejorando su concentración en ácido oleico. La co-digestión anaerobia de subproductos agrícolas y purines mejora el BMP de la mezcla de sustratos en comparación con la digestión única de purines. Se obtuvieron mayores valores de BMP con la adición de los sustratos agrícolas, lo que confirma el mejor rendimiento de los sistemas en co-digestión a niveles de inclusión adecuados. Las combinaciones con tomate, pimiento y melocotón al nivel de inclusión 3 (50% de SV) alcanzaron el mayor BMP. Esto supuso un incremento del BMP del 41% con tomate, 44% con pimiento, 28% con melocotón y 12% con caqui. Los sustratos vegetales mostraron un mayor contenido en lípidos, prote
[CAT Actualment, la sostenibilitat del sector porcí depèn de la seua capacitat per a respondre a l'elevada demanda de productes ramaders derivada del creixement de la població, adaptant-se als canvis en els contextos econòmic i polític, i millorant el seu rendiment mediambiental mitjançant la mitigació del seu impacte ambiental. En aquest context, l'ús de subproductes agroindustrials ofereix matèries primeres alternatives en producció animal, amb una menor càrrega ambiental associada, en forma de pinsos per al bestiar, font de compostos bioactius o matèries primeres útils en la producció de bioenergia. Aquesta tesi doctoral pretén avaluar l'ús de subproductes agroindustrials mediterranis com a ingredients en pinsos per al bestiar porcí o com co-substrats per a la producció de biogàs. Amb aquest objectiu, es van dissenyar i realitzar quatre assajos per a avaluar l'ús de subproductes de la indústria de l'oli d'oliva i del suc de taronja en alimentació porcina, avaluant el seu valor nutricional i les conseqüències de la seua inclusió sobre el rendiment i la salut dels animals, la qualitat del producte final i les emissions de gasos dels purins. A més, es va realitzar un assaig per a avaluar l'efecte de quatre substrats agrícoles sobre el potencial bioquímic de metà (BMP) en co-digestió anaeròbia amb purins. Els resultats obtinguts a partir dels assajos de valor nutricional indiquen que les trotes d'oliva i les polpes de taronja assajades poden ser incloses en la dieta amb canvis associats en l'excreció de nutrients que condueixen a modificacions en les emissions potencials d'amoníac i BMP dels purins. Quant als subproductes de la torta d'oliva, l'assaig de valor nutricional amb tortes d'oliva crues (COC) i parcialment desengreixades (PDOC) va mostrar que totes dues coques són fonts apreciables de fibra insoluble, però tenen un valor energètic limitat (11.2 i 7.4 MJ/kg MS per a COC i PDOC respectivament) i un baix valor com a font de proteïnes. En canvi, les polpes de taronja deshidratades (DOP) i ensitjada assecada al sol (ESDOP) assajades són una font d'energia rellevant (14.2 i 13.2 MJ/kg MS per a DOP i ESDOP respectivament) amb valor afegit a causa del seu contingut en fibra soluble. Pel que fa als assajos d'emissions in vitro, els subproductes assajats van generar una disminució en l'excreció de N en l'orina i, en el cas de la polpa d'oliva, un augment de l'excreció de matèria seca en femtes. L'emissió d'amoníac per kg de purí va disminuir amb la inclusió de torta d'oliva i polpa de taronja, mentre que el BMP per animal i dia es va veure negativament afectat per la inclusió de torta d'oliva obtenint un major BMP amb aquests subproductes. Quant als assajos de rendiments productius, la PDOC i la DOP poden incloure's en la dieta fins a 120 i 240 g/kg respectivament, sense efectes negatius en el cas de la PDOC i efectes menors per a la DOP sobre els rendiments productius, la composició corporal i la qualitat de la canal. La inclusió de PDOC i DOP no va afectar els recomptes microbians ni al volum, la composició i l'emissió global de gasos dels purins. A més, es van observar efectes beneficiosos sobre el greix subcutani amb la inclusió de PDOC, millorant la seua concentració en àcid oleic. La co-digestió anaeròbia de subproductes agrícoles i purins millora el BMP de la mescla de substrats en comparació amb la digestió única de purins. Es van obtenir majors valors de BMP amb l'addició dels substrats agrícoles, la qual cosa confirma el millor rendiment dels sistemes en co-digestió a nivells d'inclusió adequats. Les combinacions amb tomaca, pimentó i bresquilla al nivell d'inclusió 3 (50% de SV) van aconseguir el major BMP. Això va suposar un increment del BMP del 41% amb tomaca, 44% amb pimentó, 28% amb bresquilla i 12% amb caqui. Els substrats vegetals van mostrar un major contingut en lípids, proteïnes, lignina i cel·lulosa que els substrats de fruita.
[EN] Nowadays the sustainability of the pig sector relies on its capability to respond to the increasing demands for livestock products that are arising from population growth, adapting to changes in the economic and policy contexts, and improving its environmental performance through the mitigation of its impact on climate. In this framework, the use of the agro-industrial by-products offers potential alternative raw materials for animal production with a lower associated environmental burden in the form of feedstuffs for livestock, source of bioactive compounds or raw materials useful in bioenergy production. This PhD thesis aims to evaluate the use of Mediterranean agro-industrial by-products as feed ingredients for pigs or co-substrates for biogas production. To fulfil these objectives, four trials were designed and conducted to evaluate the use of olive oil and orange juice industry by-products in swine nutrition, assessing its nutritional value and the consequences of its inclusion in the diet on animals' performance and health, final product quality traits and gas emissions associated to the pig slurry. Additionally, one more trial was conducted to evaluate the effect of four agricultural substrates (tomato, pepper, peach and kaki) on the biochemical methane potential (BMP) in anaerobic co-digestion with pig slurry, focusing on the type of substrate and its inclusion level on the final substrate's mixture. The results presented in this PhD Thesis from the nutritional value assays indicate that the olive cakes and orange pulps tested can be potentially included in pig diets with associated changes in urine and faeces nutrients excretion that leads to modifications in the potential ammonia and BMP emissions from slurries. Concerning olive cake by-products, the nutritional value assay designed to test the crude (COC) and partially defatted (PDOC) olive cakes showed that they are appreciable sources of insoluble fibre but have limited energy value (11.2 and 7.4 MJ/kg DM for COC and PDOC respectively) and a low value as protein source. On the contrary, the dehydrated (DOP) and ensiled sun-dried (ESDOP) orange pulps tested are a relevant energy source (14.2 and 13.2 MJ/kg DM for DOP and ESDOP respectively) with added value in terms of SF concentration. With respect to the in vitro potential ammonia and BMP emissions assays, the by-products tested led to a decreased N excretion in urine and, in the case of the OC, increased DM excretion in faeces. The ammonia emission per kg of slurry decreased with the inclusion of olive cake and orange pulp, whereas the BMP per animal and per day was negatively affected by the inclusion of olive cake obtaining higher BMP with these by-products. Regarding the performance assays, the PDOC and the DOP may be included in balanced pig diets at rates of up to 120 and 240 g/kg respectively, without negative effects in the case of PDOC and minor effects for DOC on growth performance, body composition and carcass quality traits. Contrary to what was expected, the inclusion of PDOC and DOP did not affect microbial counts nor excreta volume, composition and global gas emission from the slurry. Additionally, beneficial effects on subcutaneous fat were observed with the inclusion of PDOC, improving its oleic acid concentration. The anaerobic co-digestion of agricultural by-products and pig slurry improves the BMP from the mixture compared to only pig slurry anaerobic digestion. Higher BMP values were obtained with increasing addition of agricultural substrate, confirming the better performance of co-digestion systems at adequate inclusion levels. In fact, combinations with tomato, pepper and peach at inclusion level 3 (50% of VS) achieved the highest BMP. This resulted in an increase in BMP of 41% with tomato, 44% with pepper, 28% with peach and 12% with kaki. Vegetable substrates (pepper and tomato) showed higher lipid, protein, lignin and cellulose content than fruit substrates (kaki and peach).
Ferrer Riera, P. (2021). Valorisation of Mediterranean agroindustrial by-products in pig production as feed and anaerobic co-digestion of slurry [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/171747
TESIS
Compendio

The Ontario biogas industry is relatively young and the overall objective of this research was to help support the growth of the industry with investigating the use of co-substrates and reactor design to enhance biogas production, recommend guidelines on the operation of full scale systems to optimize performance and characterize digestate quality. Laboratory studies evaluated the use of various substrates in the co-digestion with liquid dairy manure. These studies were used to establish ultimate biogas yields, % volatile solids (VS) reduction and minimum hydraulic retention times (HRTs). Box-Wilson Central Composite design models for corn thin stillage and waste grease (as co-substrates with dairy manure) suggest methane yields optimize with increasing proportion of the feed VS from co-substrates (constant total VS in all assays) and increasing temperatures; however, temperature had a great effect. Bench scale studies were conducted to determine a change in digester design to optimize biogas yields and increase digestate stability. A two-phase digestion system was implemented for co-digestion systems using thin stillage and waste grease with dairy manure, and methane yields showed to increase by over 22% when compared with single-phase systems. Based on current FIT contracts of 18 to 20¢/kWhe, the increased electricity and heat production could make the two-phase system economically attractive for producers. Organic loading rates (OLRs) over 4.4 g VS/L led to digester upset and OLRs of over 4.2 g VS/L·day are not recommended. On-farm anaerobic digester systems were studied for digester performance and digestate quality. Residual biogas potential (RBP) yields were effective at evaluating the stability of digestate and the U.K. PAS 110:2014 limit of 0.45 L biogas/g VS (28 days incubation) was assessed too lenient for the Ontario systems studied. A limit of 0.25 L biogas/g VS after 28 days of incubation or 0.45 L biogas/g VS after 60 days of incubation are recommended. VS reductions ranged from 56 to 76% and easily achieved the O. Reg. 267/03 regulated 50% VS reduction. E.coli and Salmonella were typically 1 to 3 logs CFU/100 mL lower than raw manure and increased HRT did not demonstrate a significant impact on the bacterial log reductions. Intermediate alkalinity (IA)/partial alkalinity (PA) proved to be a valuable tool in determining potential digester upset and has been recommended as a standard performance parameter for on-farm systems.

Dans le contexte du réchauffement climatique et de la diminution des réserves de combustibles fossiles, la biomasse lignocellulosique peut fournir une source renouvelable d'énergie, de matériaux et de produits chimiques. En particulier, la production de biogaz par méthanisation est en plein essor. C’est dans ce contexte de bioraffinerie environnementale que se situe ce projet de thèse. Il porte sur deux biomasses lignocellulosiques différentes : le sorgho et le miscanthus ayant l'avantage de combiner un fort potentiel de production de biomasse avec un impact minimal sur l'environnement. Pour ce type de biomasse, il est bien connu que la lignine joue un rôle de barrière à l’accessibilité des composés. Cette thèse a pour objectif de d’étudier l’impact des pré-traitements alcalins, connus pour délignifier la biomasse de manière efficace et ainsi améliorer son bioaccessibilité et donc sa dégradation par digestion anaérobie. L’étude de l’impact de ces pré-traitements sur la composition biochimique des biomasses et leur production méthane a montré que ces impacts diffèrent en fonction de la biomasse et des conditions opératoires des pré-traitements appliqués (réactif, durée, température, teneur en eau). Dans un objectif d’application de co-digestion en méthanisation agricole, l’impact de certains des prétraitements de ces deux biomasses a été étudié lors d’essais en réacteurs batch à recirculation. Le sorgho s’est révélé être un co-substrat adéquat du fumier. Enfin, l’étude originale des mécanismes d’action de ces pré-traitements à l’échelle de la structure anatomique de la biomasse a montré que les pré-traitements agissent différemment suivant la localisation et le type de lignine. Ces travaux de thèse permettent donc une meilleure compréhension de l’impact des pré-traitements sur différentes biomasses lignocellulosiques
In the context of global warming and declining fossil fuel reserves, lignocellulosic biomass can provide a renewable source of energy, materials and chemicals. In particular, biogas production by anaerobic digestion is facing a fast development. This thesis project takes place in this biorefinery concept. Two different lignocellulosic biomasses, which present the advantage of combining high biomass production potential with minimal environmental impact, were studied. For this kind of biomass, it is well known that lignin acts as a barrier to the accessibility of compounds. The objective of this thesis was to study the impact of alkaline pre-treatments, known be efficient in biomass delignification and thus improve its bioaccessibility and its degradation by anaerobic digestion. The study of the impact of these pre-treatments on the biochemical composition of biomasses and their methane production showed that these impacts were different according the biomass and the operating conditions of the applied pre-treatments (reagent, duration, temperature, water content). With the aim of applying it in agricultural anaerobic co-digestion context, the impact of some of these pre-treatments of sorghum and miscanthus was studied in leach bed reactors. Sorghum was found to be an adequate co-substrate for manure. Finally, the original study of the mechanisms of action of these pre-treatments at the biomass anatomical structure scale showed that the pre-treatments act differently depending on the location and type of lignin. This thesis work therefore allows a better understanding of the impact of pre-treatments on different lignocellulosic biomasses

The application of anaerobic digestion (AD) as a sustainable waste management technology is growing worldwide, due to high energy prices as well as increasingly strict environmental regulations. The growth of the AD industry necessitates exploring new substrates for their utilisation in AD processes. The present work investigates the AD of two recalcitrant biomass: lignocelluloses and keratin-rich residues. The complex nature of these waste streams limits their biological degradation; therefore, suitable pre-processing is required prior to the AD process.In the first part of the study, the effects of organic solvent pre-treatments on bioconversion of lignocelluloses (straw and forest residues) to biogas were evaluated. Pre-treatment with N-methylmorpholine-N-oxide (NMMO) resulted in minor changes in the composition of the substrates, while their digestibility significantly increased. Furthermore, due to the high cost of the NNMO, the effect of pre-treatment with the recycled solvent was also explored. Since it was found that the presence of small traces of NMMO in the system after the treatment has inhibitory effects on AD, pre-treatments of forest residues using other organic solvents, i.e. acetic acid, ethanol, and methanol, were investigated too. Although pre-treatments with acetic acid and ethanol led to the highest methane yields, the techno-economical evaluation of the process showed that pre-treatment with methanol was the most viable economically, primarily due to the lower cost of methanol, compared to that of the other solvents.In the second part of the work, wool textile wastes were subjected to biogas production. Wool is mainly composed of keratin, an extremely strong and resistible structural protein. Thermal, enzymatic and combined treatments were, therefore, performed to enhance the methane yield. The soluble protein content of the pre-treated samples showed that combined thermal and enzymatic treatments had significantly positive effects on wool degradation, resulting in the highest methane yields, i.e. 10–20-fold higher methane production, compared to that obtained from the untreated samples.In the last part of this thesis work, dry digestion of wheat straw and wool textile waste, as well as their co-digestion were studied. The total solid (TS) contents applied in the digesters were between 6–30% during the investigations. The volumetric methane productivity was significantly enhanced when the TS was increased from 6 to 13–21%. This can be a beneficial factor when considering the economic feasibility of large-scale dry AD processes.

This study aimed at seeking for the solution to recover the energy from agriculture waste in the Mekong Delta, Vietnam. The spent mushroom compost - a residue from the mushroom growing - was chosen for co-digestion with pig manure in anaerobic batch and semi-continuous experiments. The results showed that in case of spent mushroom compost made up 75% of the mixed substrate, the gained biogas volume was not significantly different compared to the treatment fed solely with 100% pig manure. The average produced biogas was 4.1 L×day-1 in the experimental conditions. The semi-continuous experiments remained in good operation up to the 90th day of the fermentation without any special agitating method application. The methane contents in both experiments were around 60%, which was significantly suitable for energy purposes. These results confirm that spent mushroom compost is possibly an acceptable material for energy recovery in the anaerobic fermentation process
Nghiên cứu này nhằm tìm kiếm giải pháp thu hồi năng lượng từ chất thải nông nghiệp tại ĐBSCL, Việt Nam. Rơm sau ủ nấm - phế phẩm sau khi trồng nấm rơm - được chọn để ủ kết hợp với phân heo trong các bộ ủ yếm khí theo mẻ và bán liên tục. Kết quả cho thấy nếu phối trộn đến 75% rơm sau ủ nấm trong nguyên liệu ủ, tổng lượng khí thu được không khác biệt đáng kể so với thí nghiệm ủ 100% phân heo. Trong điều kiện thí nghiệm, lượng khí thu được trung bình là 4.1 L.ngày-1. Thí nghiệm ủ bán liên tục vẫn vận hành tốt ở ngày thứ 90 mặc dù mẻ ủ không được khuấy đảo. Hàm lượng khí mê-tan đo được chiếm khoảng 60% hoàn toàn có thể sử dụng cho các nhu cầu về năng lượng. Những kết quả thí nghiệm khẳng định có thể sử dụng rơm sau ủ nấm để thu hồi năng lượng thông qua quá trình ủ yếm khí kết hợp

In this thesis, the anaerobic co-digestion of thickened waste activated sludge (TWAS) and, fat, oil and grease (FOG) was investigated as a method for TWAS:FOG treatment, stabilization, reduction and conversion to bio-methane gas as a valuable source of renewable energy. In the first phase, thermophilic and hyper-thermophilic anaerobic co-digestion of TWAS and FOG were investigated and compared. 20 – 80%FOG (based on total volatile solids) were tested using two sets of biochemical methane potential assays (BMP). Hyper-thermophilic co-digestion of TWAS with up to 60%FOG was shown to significantly increase the methane production and VS reduction as compared to the thermophilic co-digestion of the same TWAS:FOG mixture and as compared to the control (TWAS thermophilic mono-digestion). Both linear and non-linear regression models were used to represent the co-digestion results. In the second phase, the feasibility of the thermophilic and hyper-thermophilic co-digestion of TWAS and FOG were more investigated using lab scale semi-continuous reactors. The dual stage hyper-thermophilic reactor was introduced for the first time in this work for co-digesting TWAS and FOG. The dual stage co-digestion reactor was shown to significantly outperform the single-stage thermophilic mono-digestion reactor (the control) and the single-stage thermophilic co-digestion reactor at all three hydraulic retention times (HRTs) considered in the study namely, 15, 12 and 9 days. The dual-stage hyper-thermophilic co-digester digested up to 70%FOG at 15 days HRT without any stressing signs and produced a methane yield that was 148.2% higher compared to the control methane yield at the same HRT. It also produced a class A effluent at all three tested HRTs and positive net energy for 15 and 12 days HRT. The effects of microwave (MW) pretreatment, and combined alkaline-MW pretreatment on the co-digestion of TWAS:FOG mixtures with 20, 40 and 60% FOG were investigated in the third phase of this study. MW pretreatment at a high temperature of 175ᵒC was shown to be the most effective MW pretreatment option in solubilizing TWAS:FOG mixtures and in boosting the methane yield. It resulted in maximum solubilization for the 20%FOG samples and maximum methane yield for samples with 60%FOG. The combined alkaline-MW (NaOH-MW) pretreatment at a pH 10 showed to be an ineffective option for TWAS:FOG pretreatment before the anaerobic co-digestion process. In the fourth phase, the effects of the three selected pretreatments on the solubilization of TWAS and 20%FOG mixture on the molecular scale were investigated. The pretreatments used included: (i) MW pretreatment at 175ᵒC (since this was the best MW pretreatment condition according to the results of phase 3), (ii) hyper-thermophilic stage @ 70ᵒC and 2days HRT (effectively used in phases 1 and 2), and (iii) conventional heat at 70ᵒC. The analysis involved separation of the solubilized substrates after pretreatment using ultrafiltration (UF) at four different sizes (1, 10, 100 and 300 kDa). The results showed that each pretreatment method uniquely changed the particle size distribution. These changes showed to affect the biodegradability of substrates with different class size. Finally, two brief studies were performed using BMP tests to investigate the feasibility of FOG addition as a biogas booster in TWAS anaerobic digestion. First, the effect of FOG addition on TWAS and organic fraction of municipal solid waste (OFMSW) co-digestion was tested using hyper-thermophilic BMP tests. The addition of 30% FOG (based on total volatile solids) was shown very effective in improving the methane yield. The 30% FOG addition to TWAS:OFMSW mixture resulted in 59.9 and 84.4% higher methane yield compared to the methane yields of TWAS:OFMSW and TWAS samples, respectively. Second, the feasibility of using the soluble part of FOG (L-FOG) as a co-digestion substrate to increase the biogas production from the thermophilic digestion of TWAS was investigated. The results showed that co-digestion of TWAS and 20 to 80% (based on total VS) of L-FOG using a substrate to inoculum ratio (S/I) of 1 improved the biogas yield by 13.5 to 83.0%, respectively. No inhibition was reported at high L-FOG %.

This work was carried out at Biogas Research Center (BRC) and the company Biogas in Vadstena. The aim was to systematically evaluate new substrates for biogas production. In particular, this case investigated the potential of straw in co-digestion with manure and slurry from pig, chicken and dairy. Straw is interesting to evaluate since it is second generation biomass and available in a large quantity. Also, anaerobic digestion (AD) of manure is beneficial because it deals with the spontaneous methane emission and leads to a better manure handling. Goals within the EU as well as in Sweden have been set up to reduce greenhouse gas emissions from fossil fuel and to produce more renewable energy. The methodology used is outlined by BRC in which a number of key areas, such as description of biomass, amount biomass, gas yield, technology, economy, environmental performance and energy system, competing interests and institutional factors, have been evaluated through literature studies and case study Biogas in Vadstena. Based on the results an overall judgment is done to determine the potential of straw. The result shows that straw is not appropriate to digest solely because of high TS, high carbon content and lack of nutrients. Straw also has lignocellulosic structures, which are difficult to break down. Especially lignin limits the biodegradability. Mechanical, thermal, chemical and biological pretreatments can increase the availability and biodegradability in the straw. In some cases pretreatment can also increase the methane potential. However, straw works well as a carbon complement in co-digestion with manure, which is a nitrogen-rich substrate. There are technologies available for AD of straw and manure for the whole biogas process, from transportation and pretreatment to digestion and upgrading. Although, there is space for further development of pretreatment and upgrading technology. The economic calculations show that it is profitable to use straw with manure in a farm-based biogas plant for vehicle gas production. Furthermore, the calculations of the energy show that biogas production is energy efficient with energy input/output ratio of 18-23%. Besides production of biogas, the digestate could be used as an environmentally friendly fertilizer. In summary, it is possible to produce biogas from straw together with manure, and this is beneficial from both an environmental and economic perspective.
Detta examensarbete har utförts i samarbete med Biogas Research Center (BRC) och företaget Biogas i Vadstena. Målet med examensarbetet var att systematiskt utvärdera nya substrat för biogasproduktion. Specifikt för det här fallet var att undersöka potentialen för halm i samrötning med gödsel och flyt från svin, höns och nöt. Halm är intressant att utvärdera då det tillhör andra generationens biomassa och finns tillgängligt i stor mängd. Även rötning av gödsel är givande då den spontana metanemissionen uteblir och det ger en bättre gödselhantering. Det har satts upp mål inom såväl EU som i Sverige att mer förnybart bränsle bör produceras för att minska växthusgasutsläppen från fossila bränslen. Metodiken som använts har framarbetats av BRC. Det innebär att substrat granskas utifrån ett flertal nyckelområden, såsom beskrivning och mängd biomassa, gasutbyte, synergieffekter, teknik, ekonomi, miljöpåverkan och energisystem, konkurrerande intressen och institutionella faktorer. Dessa har utvärderats genom litteraturstudier och studie av fallet Biogas i Vadstena. Utifrån resultatet görs en övergripande bedömning av substratet. Resultatet visar att halm inte är lämpligt att röta enskilt på grund av högt TS-värde, högt kolinnehåll och att den är näringsfattig. Halm består även till stor del av lignocellosa-strukturer som är svåra att bryta ned, i synnerhet lignin. Mekaniska, termiska, kemiska och bioglogiska förbehandlingar kan öka tillgängligheten och nedbrytbarheten av halm. Det kan även öka metanpotentialen i vissa fall. Däremot fungerar halm bra som ett komplement i samrötning med gödsel som är ett kväverikt substrat. Det finns teknik för rötning av halm för hela biogasprocessen, från transport, förbehandling och rötning till uppgradering. Dock finns utrymme för tekniken att utvecklas ytterligare. De ekonomiska beräkningarna visar att det är lönsamt att använda halm tillsammans med gödsel i en jordbruksbaserad biogasanläggning för fordonsgasproduktion. Vidare visar beräkningar för energisystemet att biogasproduktion är energieffektiv med energi input/output-kvot på 18-23%. Förutom fordonsgas produceras även biogödsel som är ett miljövänligt alternativ till konstgjord gödsel. Sammanfattningsvis, det är möjligt att producera biogas av halm tillsammans med gödsel och det är fördelaktigt ur en såväl miljömässigt som ekonomiskt perspektiv.

Mestrado em Engenharia do Ambiente - Instituto Superior de Agronomia
Over the last decades, phytodepuration has been considered an efficient technology to treat agricultural wastewaters. Swine wastewater is rich in nutrients that can be used to grow biomass, producing a treated wastewater that can be used for irrigation and a biomass that may be useful for potential energy production by anaerobic digestion (AD). In this study a comparative polishing treatment assays were developed, at a bench scale, through Lemna minor growth in swine wastewater (4%) with similar concentration at a real scale last lagoon and Lemna minor growth in synthetic medium. The highest observed growth rate obtained in swine wastewater was 28.7 ± 2.3 g m-2 day-1 or 3.1 ± 0.3 gDM m-2 day-1. The highest nitrogen and phosphorus uptake rates in swine wastewater system were 140 mg m-2 day-1 and 3.47 mg m- 2 day-1, respectively. The COD removal efficiency was 60.0 ± 1.0%. Furthermore, an integrated approach was investigated assessing possible valorisation of biomass by anaerobic co-digestion of swine wastewater with Lemna minor. Results showed a clear improvement in gas production rate and methane specific production in 40% and 44%, respectively, when compared to mono-substrate digestion

This PhD thesis aimed at evaluating the performance of high rate algal ponds (HRAP) to post-treat the anaerobic effluent from an upflow anaerobic sludge blanket (UASB) reactor fed with sewage. The work analysed the system complishment in terms of treatment efficiency, micropollutants removal and biogas production, through the anaerobic co-digestion of raw sewage and microalgal biomass (with and without solar thermal pre-treatment), in a demonstration-scale system. In addition, the research intended at assessing the sustainability of the UASB+HRAP system using life cycle assessment (LCA), in terms of its environmental impact in comparison with other UASB post-treatment technologies. Sewage treatment efficiency was analysed through BIO_ALGAE 2 mathematical model, which enabled the understanding and optimisation of the symbiotic relation between microalgae and bacteria. To this, experimental data from demonstrationscale systems in tropical climate conditions were used for model calibration. In addition, different scenarios were considered by varying HRAP hydraulic retention time (HRT) (4, 6 and 8 days). Results obtained showed an efficient removal of COD (70%), TSS (42%), N-NH4 (57%) and P-PO4 (30%) in the UASB+HRAP system. From the valuated scenarios, the operation of HRAP at 4 days of HRT showed to be optimal in terms of sewage treatment and energy production, with lower area requirement. Regarding the removal of micropollutants (pharmaceuticals and endocrine disruptors), amples were collected periodically from raw sewage, UASB reactor and HRAP effluents. All monitored compounds were found in raw sewage, with occurrence rates ranging from 70 to 100%. Micropollutant removal in the UASB reactor ranged from none (-25.12% for the hormone EE2-ethinylestradiol) to 85% removal (E2-estradiol), due to the incapacity of anaerobic processes. However, the overall UASB+HRAP system was highly efficient for removing most compounds, with removal rates ranging between 65% (ibuprofen) to 95% (estrone). To evaluate the co-digestion of raw sewage and microalgal biomass in UASB reactors two phases were considered: without and after thermal pre-treatment using solar heating. In both cases, an UASB reactor fed with only raw sewage was used as control. During the first phase, the results showed a methane yield increase of 35% after anaerobic co-digestion with microalgae, from 156 to 211 NL CH4 kg-1 VS. An energy assessment showed a positive energy balance, with an annual average net ratio of 2.11 in the UASB+HRAP system. Regarding the results after microalgal biomass pre-treatment, organic matter solubilization reached 32% increase in terms of total COD. Furthermore, methane yield was increased by 45% compared to mono-digestion with raw sewage, from 81 to 117 NL CH4 kg-1 COD. The energy assessment showed a positive energy balance, with an annual average net ratio of 2.52 in the sewage treatment system. Finally, the environmental impact of HRAP as post-treatment technology following UASB reactors was carried out using LCA for comparison with other post-treatments: trickling filters, polishing ponds and constructed wetlands. The results showed that among the 8 categories evaluated, HRAP showed better performance in 4 of them. The study concluded that HRAP may be considered a potential technology following UASB reactors and its environmental impacts can be further improved by using appropriate materials and construction techniques.
Esta tesis tuvo como objetivo evaluar el desempeño de lagunas de alta tasa (LAT) como postratamiento del efluente anaeróbico de un reactor UASB depurando aguas residuales domésticas. El trabajo analizó el desempeño de este sistema evaluando la eficiencia del tratamiento, remoción de microcontaminantes y producción de biogás, mediante la codigestión anaeróbica de aguas residuales brutas y biomasa de microalgas (con y sin pre-tratamiento térmico solar), en escala de demonstración. Además, esta investigación también evaluó el impacto ambiental del flujo de tratamiento UASB + LAT, utilizando de la herramienta de evaluación del ciclo de vida (ACV), comparándolo con otros flujos de tratamiento ya consolidados para la realidad brasileña. La eficiencia de la depuración de las aguas residuales se analizó por el modelo matemático BIO_ALGAE 2, que permitió comprender y optimizar la relación simbiótica entre microalgas y bacterias. Para ello, se utilizaron datos experimentales del sistema en escala de demostración y en condiciones climáticas tropicales para calibrar el modelo. Además, a partir del modelo calibrado, se simularon diferentes escenarios variando el tiempo de detención hidráulico (TDH) de las lagunas (4, 6 y 8 días). Los resultados mostraron una eficiente remoción de DQO (70%), SST (42%), N-NH4 (57%) y P-PO4 (30%) en el sistema UASB + LAT. De los escenarios evaluados, la operación de las LAT con 4 días de TDH resultó excelente para la depuración de aguas residuales y potencial de producción de energía, con menor necesidad de área. Acerca de la remoción de microcontaminantes (fármacos y disruptores endocrinos), periódicamente se recolectaron muestras de las aguas residuales sin tratar, reactor UASB y efluentes de las lagunas. Todos los compuestos monitoreados se encontraron en las aguas residuales sin tratar, con tasas de ocurrencia que oscilan entre el 70 y el 100%. La eliminación de los microcontaminantes en el reactor UASB osciló entre nada (-25,12% para la hormona EE2-etinilestradiol) y 85% de eliminación (E2-estradiol), debido a la incapacidad de los procesos anaeróbicos. Sin embargo, el sistema UASB + LAT en general fue muy eficaz en la eliminación de la mayoría de los compuestos, con tasas de eliminación que desde el 65% (ibuprofeno) al 95% (estrona). Para evaluar la codigestión de aguas residuales sin tratamiento y biomasa de microalgas en reactores UASB, se consideraron dos fases: sin y después del pretratamiento térmico con calentamiento solar. En ambos casos, se utilizó como control un reactor UASB alimentado solo con aguas residuales sin tratar. Durante la primera fase, los resultados mostraron un aumento del 35% en el rendimiento de metano después de la co-digestión anaeróbica con microalgas, de 156 NL CH4 kg-1 SV a 211 NL CH4 kg-1 SV. Una evaluación energética demostró un balance positivo, con un ratio medio anual entre energía producida y consumida de 2,11 en el sistema UASB + LAT. En cuanto a los resultados tras el pretratamiento de la biomasa de microalgas, la solubilización de la materia orgánica alcanzó una eficiencia del 32% en términos de DQO total. Además, el rendimiento de metano aumentó en un 45% en comparación con la mono-digestión con aguas residuales sin tratar, de 81 NL CH4 kg-1 DQO a 117 NL CH4 kg-1 DQO. La valoración energética arrojó un saldo positivo, con una ratio medio anual entre energía producida y consumida de 2,52 para el sistema evaluado. Finalmente, el impacto ambiental del LAT como postratamiento de efluentes de reactores UASB se llevó a cabo utilizando LCA como comparación con otras tecnologías ya consolidadas para el postratamiento del reactor UASB en Brasil: filtro biológico percolador, lagunas de pulimiento y humedal construido. Los resultados mostraron que, entre las 8 categorías evaluadas, el sistema LAT se desempeñó mejor en 4. El estudio concluyó que LAT puede considerarse una tecnología potencial y sostenible para el postratamiento de efluentes de reactores UASB y sus impactos ambientales pueden mejorarse utilizando materiales y técnicas de construcción adecuada.
Esta tese teve como objetivo avaliar o desempenho de lagoas de algas de alta taxa (LAT) como pós-tratamento do efluente anaeróbio de um reator UASB alimentado com esgoto doméstico. O trabalho analisou o desempenho desse sistema em termos de eficiência de tratamento, remoção de micropoluentes e produção de biogás, através da co-digestão anaeróbia de esgoto bruto e biomassa microalgal (com e sem pré-tratamento solar térmico), em escala de demonstração. Além disso, essa pesquisa também a avaliou o impacto ambiental do fluxo de tratamento UASB+LAT, através da ferramenta de avaliação do ciclo de vida (ACV), comparando com outros fluxos de tratamento já consolidados para a realidade brasileira. A eficiência do tratamento de esgoto foi analisada por meio do modelo matemático BIO_ALGAE 2, que possibilitou o entendimento e otimização da relação simbiótica entre microalgas e bactérias. Para isso, dados experimentais do sistema em escala de demonstração e em condições de clima tropical foram utilizados para calibração do modelo. Ademais, a partir do modelo calibrado, diferentes cenários foram simulados variando o tempo de detenção hidráulica (TDH) das LAT (4, 6 e 8 dias). Os resultados obtidos mostraram uma remoção eficiente de DQO (70%), SST (42%), N-NH4 (57%) e P-PO4 (30%) no sistema UASB + LAT. Dos cenários avaliados, a operação das LAT com 4 dias de TDH mostrou-se ótima em termos de tratamento de esgoto e potencial de produção de energia, com menor necessidade de área. Em relação à remoção dos micropoluentes (fármacos e desreguladores endócrinos), foram coletadas periodicamente amostras de esgoto bruto, reator UASB e efluentes das Lagoas. Todos os compostos monitorados foram encontrados no esgoto bruto, com taxas de ocorrência variando de 70 a 100%. A remoção do micropoluente no reator UASB variou de nenhum (-25,12% para o hormônio EE2-etinilestradiol) a 85% de remoção (E2-estradiol), devido à incapacidade dos processos anaeróbicos. No entanto, o sistema UASB + LAT em geral foi altamente eficiente para remover a maioria dos compostos, com taxas de remoção variando entre 65% (ibuprofeno) a 95% (estrona). Para avaliar a co-digestão de esgoto bruto e biomassa microalgal em reatores UASB foram consideradas duas fases: sem e após pré-tratamento térmico com aquecimento solar. Em ambos os casos, um reator UASB alimentado apenas com esgoto bruto foi usado como controle. Durante a primeira fase, os resultados mostraram um aumento no rendimento de metano de 35% após a co-digestão anaeróbia com microalgas, de 156 NL CH4 kg-1 SV para 211 NL CH4 kg-1 SV. Uma avaliação energética mostrou um balanço energético positivo, com uma relação média anual entre energia produzida e consumida de 2,11 no sistema UASB+LAT. Em relação aos resultados após o pré-tratamento da biomassa microalgal, a solubilização da matéria orgânica atingiu uma eficiência de 32% em termos de DQO total. Além disso, o rendimento de metano aumentou em 45% em comparação com a mono-digestão com esgoto bruto, de 81 NL CH4 kg-1 DQO para 117 NL CH4 kg-1 DQO. A avaliação energética apresentou balanço positivo, com relação média anual entre energia produzida e consumida de 2,52 para o sistema avaliado. Finalmente, o impacto ambiental das LAT como pós-tratamento de efluente de reatores UASB foi realizado usando ACV para comparação com outras tecnologias já consolidadas para o pós-tratamento de reator UASB no Brasil: filtro biológico percolador, lagoas de polimento e wetland construído. Os resultados mostraram que dentre as 8 categorias avaliadas, o sistema de LAT apresentou melhor desempenho em 4. O estudo concluiu que as LAT podem ser considerado uma tecnologia potencial e sustentável para pós tratar efluente de reatores UASB e seus impactos ambientais podem ser melhorados usando materiais e técnicas de construção apropriados
Enginyeria ambiental

Uncertainty about anaerobic digestion process stability is the main issue preventing more widespread use of the process as a source of energy recovery in wastewater treatment facilities. The overall objective of this research was to study the feasibility of enhancing biogas production inside wastewater facilities using co-digestion of municipal sludge with bakery waste. Another objective was to improve the stability index and a mathematical model that can be useful tools to predict the process stability of municipal sludge digestion alone, and when it is mixed with bakery waste, as a substrate for microorganisms. Experiments were conducted in three phases. In phase 1, a full-scale anaerobic digester at Central Weber Sewer Improvement District, Ogden, UT, receiving a mixture of primary and secondary sludge, was monitored for one hundred days. Chemical oxygen demand (COD), and volatile solids (VS) mass balances were conducted to evaluate the stability of the digester and its capability of producing methane gas. The COD mass balance accounted for nearly 90% of the methane gas produced while the VS mass balance showed that 91% of the organic matter removed resulted in biogas formation. Other parameters monitored included: pH, alkalinity, VFA, and propionic acid. The values of these parameters showed that the digester was running under stable steady state conditions. At mesophilic temperature, the stability index was determined and equal to 0.40 L (CH4)/ g(ΔVS) In phase 2, the feasibility of adding BW to MS was tested in batch reactors scale. The biogas production was enhanced and the digester was stable until the range of 37- 40% of BW to 63-60% of MS. The ADM1 coefficients were modified to accurately predict the digester performance. The modified model outputs (pH, VFA, and methane) were within acceptable ranges when compared with the observed data from the batch reactors. In phase 3, the feasibility of MS and BW were tested using an Induced Bed Reactor (IBR) with a 50:50% ratio of MS:BW (COD basis). The process was stable during different hydraulic retention times and the ADM1 was modified to predict the stability of the process in the IBR.

Australia is one of the major producers and exporter of agricultural products. Annually, Australian agriculture produces approximately 151 Tg CO2 equivalent emissions. The use of fossil fuels in crop cultivation, harvesting and transportation are considered as the primary source of these greenhouse gas (GHG) emissions. Moreover, agronomic management and crop residues left in the field also contribute to these GHG emissions. Alternative waste management practices include the use of crop residues and agro-wastes as feedstocks for bioenergy production. Anaerobic digestion is considered as sustainable environmental technology to convert industrial sugarcane residues to carbon dioxide (CO2) - neutral biogas. The biogas thus produced can be used to produce heat, electricity and upgrade to biomethane for vehicle use. The produced biomethane can replace the diesel consumption associated with GHG emission in cane transport. Sugarcane is one among the most cultivated crop in the world. Australia alone produced nearly 33.5 million tonnes of cane in 2018 (FAO 2018). These large production of sugarcane lead to an increase in crop residues and agro-wastes from the sugarcane industry. In this study, an investigation regarding the anaerobic co-digestion of crop residues and agro-wastes from sugarcane industry viz, sugarcane trash (SCT) or sugarcane bagasse (SCB) with chicken manure (CM) was investigated in a batch experiment at 37 °C. In spite of various researches conducted till date about co-digestion of lignocellulosic waste with manure, no research data was available regarding the effect of feed ratio on co-digestion of SCT/SCB with CM. This research gap was investigated in this study. In addition to this, steam explosion pre-treatment of SCT/SCB was included to investigate how the pre-treatment influence methane yield among different feed ratios of SCT/SCB with CM. At first, SCT and SCB were subjected to steam explosion pre-treatment (steam impregnation at 130 °C for 5 minutes followed by steam explosion). Later, two sets of biochemical methane potential (BMP) tests were conducted at an Inoculum to Substrate Ratio (ISR) of 2. Co-digestion of untreated and steam exploded SCT or SCB with CM was investigated at feed ratios of 75:25, 50:50 and 25:75 on volatile solids (VS) basis. Assays with 100% untreated and steam exploded SCT or SCB were also included. Chemical analysis revealed that the steam explosion improved the VS content in pre-treated biomass compared with untreated biomass. The increase in VS was 1.6% and 5.7% in SCT and SCB, respectively. On the other hand, a slight reduction in total solids (TS) of nearly 4% and 1% were observed in the case of SCT and SCB, respectively. BMP results showed that the steam explosion had a profound effect on the methane production rates and yields, especially for SCB than SCT. Methane (CH4) yields of 201.8 and 199 ml CH4/gVSadded were obtained during the mono-digestion of untreated SCT and SCB, respectively. The corresponding values for 100% steam-exploded SCT and SCB were 207.5 and 225.6 ml/gVSadded, respectively. In comparison to mono-digestion, the co-digestion of SCB or SCT with CM did not improve the methane yields. Nevertheless, pre-treatment improved the methane production rates and yields of pre-treated biomass than untreated biomass. Among the studied feed ratios, best methane yields of 206.5 ml/gVSadded were obtained when steam-exploded SCT was co-digested with CM at 75:25 ratio. However, methane yields decreased with an increase in the amount of CM added. SCB also showed a similar trend. The best methane yield of 199.5 ml/gVSadded was obtained when steam-exploded SCB was co-digested with CM at 75:25 ratio. Among the tested feed ratios, all co-digestion mixtures except for 75:25 and 50:50 ratios of untreated SCT to CM showed synergistic effects. The best synergistic effect of 18.57% was observed when untreated SCB was co-digested with CM at 25:75 ratio. Kinetic modelling results confirmed that the steam explosion pre-treatment improved the methane production rates and yields by increasing the hydrolysis rate constant values. However, a higher hydrolysis rate constant was noticed for SCT than SCB. The highest hydrolysis rate constant of 0.16 d-1 was achieved at feed ratios of 50:50 and 25:75 of pre-treated SCT:CM. Interestingly, more than 75% of methane in pre-treated assays was produced by Day 11. The study thus suggests that the steam explosion can improve the methane production rates, yields and productivity of SCT and SCB. However, the use of CM as co-substrate did not improve the methane yields when compared to the mono-digestion of SCT or SCB, but a positive synergism was evident in most of the co-digestion feed ratios.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

Today's society is facing major challenges. In order to reduce the climate impact fossil fuels should be replaced with fuels that do not contribute to the greenhouse effect. The growing population generates organic waste originating from industry and households so called organic fraction of municipal solid waste (OFMSW). Through anaerobic digestion, waste can be utilized to produce energy-rich methane gas. In this way, waste can be a resource instead of a burden on society. The purpose of this project is to investigate the methane yield of source-sorted organic fraction of municipal solid waste (SS-OFMSW) pretreated with screw crush technology and methane yield at the co-digestion of food waste and biosludge from paper mills. SS-OFMSW which is either pre-treated in a screw crusher or a Food Waste Mill and a mixture of SS-OFMSW and biosludge from paper mills digested in a semi - continuous wet process under mesophilic conditions with a retention time of 20 days. Screw crush technique gave a slurry with a methane yield of about 440-490 mL / g VS, which was slightly higher than the yield of 300-350 mL / g VS from the slurry pretreated with Food Waste Mill. The methane concentration was slightly higher for slurry pretreated with Food Waste Mill, 74% in average compared with 68% for slurry pretreated with screw crush. Biosludge from paper mills is an organic waste that can be digested in order to produce biogas. The sludge is poor in nutrients and methane yield at individual anaerobic digestion of paper mill sludge is relatively low. In this study, biosludge was co-digested with SS-OFMSW. The mixture with the proportions 1:1 by g VS gave a methane yield of about 420-480 mL / g VS which is higher than the constituent substrates digested separately. Co-digestion gave a methane concentration at 80% which is also higher than at the individual anaerobic digestion of substrates.

Notre société évolue constamment et se positionne vis-à-vis du monde qui l’entoure. Cette évolution la pousse à se réorganiser atour d’énergie provenant de source locale et renouvelable. Pour ces raisons, il semble pertinent de concevoir une évolution possible de la méthanisation par des unités localisées. On parle alors de micro-méthanisation à l’échelle urbaine. La rédaction de cette thèse a ainsi eu pour objectif d’apporter des éléments de réponse quant à la question de la faisabilité d’intégrée cette micro-méthanisation dans des quartiers. Pour cela, il a été réalisé : i) Une analyse des retours d’expérience issus de villes porteuses de projet de méthanisation urbaine. ii) Une approche expérimentale, dans le but d’obtenir un processus de méthanisation des déchets urbains à l’échelle laboratoire. iii) Ces données d’entrée ont ensuite permis l’établissement d’un modèle de valorisation des déchets dans un quartier. Ces résultats mettent en avant la nécessité d’une approche systémique afin de pouvoir intégrer la méthanisation dans un quartier. Ils permettent de plus, de recommander l’utilisation de certains procédés et l’emploie de déchets, afin d’améliorer la mise en œuvre du processus dans l’espace urbain. Dans des conditions définies la méthanisation urbains est possible et stable dans le temps. De plus, le bilan énergétique s’avère bénéfique pour le quartier. On note que l’énergie ainsi produite, l’est majoritairement sous forme de chaleur ce qui met en avant l’intérêt d’un processus intégré, proche des habitations
Our society is constantly evolving and positioning itself in relation to the world around it. This evolution pushes it to reorganize itself around energy from local and more renewable sources. For these reasons, it seems appropriate to design a possible evolution of anaerobic digestion (AD) by localized units. This is referred to a micro-AD at urban scale. The purpose of this thesis was to provide some answers to the question of the feasibility of integrating this micro-AD into a neighbourhood.To this end, it was carried out: i) An analysis of feedback from cities with urban AD projects. ii) An experimental approach, with the aim of obtaining a stable AD process of urban waste atlaboratory scale. iii) These input data then made it possible to establish a waste recovery model in a district. These results highlight the need for a systemic approach in order to be able to integrate AD in a neighbourhood. They also make it possible to recommend processes and wastes, in order to improve the implementation of the process in urban areas. Under defined conditions, urban AD is possible and stable over time. In addition, the energy balance is beneficial for the district. It should be noted that the energy thus produced is mainly in the form of heat, which highlights the importance of an integrated process, close to homes

Les deux principaux objectifs de cette thèse sont de développer les aspects théoriques et expérimentaux sur la co-méthanisation des déchets fermiers et alimentaires. Les objectifs de nos études portent sur l'élimination du maximum de déchets mis en ISDND, la réduction des pollutions des milieux naturels (eau, sol, air) par les effluents d'élevage, les boues de STEP et sur la mise en disposition d'une source énergétique renouvelable via le biogaz obtenu. Premièrement, nous avons effectué des expérimentations sur la co-méthanisation des effluents liquides, lisier de porc, boues de STEP, et de la vinasse et le mélange de ces effluents d'élevage avec les déjections solides des animaux (fumier, fientes) et des biodéchets (restes de repas). Ces expérimentations avaient pour but de suivre l'évolution du milieu réactionnel en fonction du composant du mélange ainsi co-digéré. Deuxièmement des tests des potentiels méthane et biogaz issus de mélange associant plusieurs types de déchets organiques sous différents états physiques (liquide, semi liquide, pâteux, solide) ont été effectués. La problématique qui se posait étant de savoir parmi les déchets à mélanger, quelle proportion de chaque mono-substrat donnera le meilleur potentiel méthanogène et s'il était possible de mettre en avant des effets synergétiques entre déchets. Nous avons fait appel à un outil statistique, le plan de mélange pour définir les mélanges à tester. Pour un mélange à 3 composants (fumier de vache, lisier de porc, restes de repas), le nombre d'expériences optimum à réaliser a été de 13. La réalisation du plan de mélange, c'est à dire la campagne expérimentale sur les co-méthanisations des 13 mélanges proposés nous a permis d'observer que le potentiel méthane d'un mélange dépend tout premièrement de sa texture (état physique) à l'entrée du processus. Un mélange contenant un maximum en proportion en co-produits liquides (lisier de porc) associé avec le maximum de déchets riches en substrats solubles (restes de repas) nous a donné les meilleurs potentiels méthane et biogaz. Cette observation a été confirmée par le taux de conversion de la matière sèche (MS) en matière volatile (MV) du mélange. Compte tenu du taux de MS, MV et le ratio MV/MS d'un mélange, ainsi que les interactions entre les composants du mélange, une loi permettant de prédire le potentiel biogaz d'un mélange doit considérer ces facteurs. Cette loi doit tenir compte de l'effet positif (synergisme) et l'effet négatif (antagonisme) entre les composants du mélange. Cette loi a été définie dans le but de prédire le potentiel méthane des mélanges constitués de fumier de vache, lisier de porc et restes de repas et se situant à l'intérieur du domaine expérimental défini par les limites sur les proportions minimale et maximale de chaque composant du mélange. Toutefois, cette loi définie n'est applicable qu'aux mélanges d'association de fumier de vache, de lisier de porc et des restes de repas. Cette loi a été définie pour estimer le BMP des mélanges, et ne permet pas de suivre le procédé de la méthanisation. Aussi, pour prédire le volume de biogaz (méthane) journalier ou cumulé de la cométhanisation
The two main objectives of this thesis are to develop theoretical and experimental aspects of the anaerobic co-digestion of farm wastes associated with food. Our general studies have for objectives the elimination as much as possible the maximum of organic waste into non-hazardous landfills, reduce pollution of natural environments (water, soil, air) by the effluent livestock, sewage sludge, and dispose of energy via the produced biogas.Firstly, we carried out experiments on the anaerobic co-digestion of the liquid effluents association (pig slurry, sewage sludge, vinasse effluents) and the mixture of animal slurries, manures, and food waste. The aim of these experiments was to follow the evolution of the reactor behavior according to the component of the co-digested mixture.Secondly, BMP tests of mixture of association several types of organic waste under different physical condition (liquid, semi liquid, pasty, solid) were carried out. We have been tried to know, which proportion of each mono-substrate will give the best BMP among waste to mix? We used a statistical tool, the mixture design to define the mixtures to be tested. For a mixture with 3 components (cow dung, pig slurry, food waste), the optimum number of experiments to realize was 13.The realization of the mixture design, i.e. the experiment series on the anaerobic co-digestion of the 13 proposed mixtures enabled us to observe that the BMP of a mixture firstly depends on its texture (physical state) at the entry of the process. A mixture containing a maximum in proportion in liquid substrate (pig slurry) associated with food waste gave us the best biogas and methane potential. This observation was confirmed by the conversion rate of dry matter to volatile solid (VS) of the mixture. These results were proven by the activity (synergism, antagonism) of mixtures components influencing to BMP tests.The empiric law defined to predict the BMP of a mixture must to account the rate of VS/DM of a mixture, and the interactions between components of the mixture. This law must also include the positive effect (synergism) and negative (antagonism) between components of the mixture. This law has been defined in order to predict the potential methane mixtures of cow dung, pig slurry and food wastes and being within the experimental domain defined by the limits on minimum and maximum proportions of each component of the mixture. However, this definite law is applicable only to the mixtures of cow dung, pig slurry and food waste. The definite law is limited for prediction of mixtures BMP. However, this empiric law can not be used to follow reactor process. Model with three stages (hydrolysis of soluble substrate, acidogenic production stage and methanogenic stage) was used to predict daily and cumulative of biogas and methane production of anaerobic digestion of farm waste associated with vegetable waste. This model must be adapted with substrate type used and experimentations conditions (batch and mesophilic conditions). An adjustment of the model equations describing hydrolysis polymers stage was necessary in order to take into account of the concentration of polymers in particulate forms contained in complex substrates such as manure, slurry, and vegetable food waste. This adapted model was called model of Coupling. Indeed, a calibration of the most influential parameters of the model of Coupling, on the output must be carried out in order to validate the model.Daily and cumulative predictions of biogas and methane production of anaerobic digestion of farm waste associated with food waste were obtained by using adapted dynamical model. Model parameters values depend on the substrate type using in experimentation processes. Moreover, parameters values must be verified, needing further work

Anaerobic digestion is perhaps the simplest and most widely accepted method for solids and residuals management in the field of wastewater treatment. An emerging trend with regard to anaerobic digestion is the addition of additional organic or industrial wastes rich in degradable material (COD) that can lead to increased methane production and reduce the energy demand of the facility. The objective of this research was to evaluate the effect of adding significant quantities (>20% of feed volume) of High Strength Food Wastes (HSW) to digesters treating conventional municipal sludge by monitoring key parameters such as pH, influent and effluent solids, ammonia, Volatile Fatty Acids (VFAs) and alkalinity. Daily gas production was also closely monitored. Four digesters were set up and exposed to different food waste loading rates. A comparison was drawn between the performance of these reactors, one of which was fed only with sewage sludge and served as the control. If the bacteria in the system are able to metabolize this additional COD, it should show up as an increase in gas production with little or no increase in effluent COD. Ammonia is another crucial parameter that needs to be closely watched as it can have an inhibitory effect on methane production. As part of this study, the impact of addition of free ammonium (simulating high ammonium concentration in the feed sludge or food waste) on digester performance was assessed. The digesters were closely monitored for signs of poor performance or failure.
Master of Science