Dissertations / Theses on the topic 'Algal Flocculation'

Algae can be used as a feedstock for agricultural fertilizers, livestock/poultry feeds, anaerobic digestion, and biofuel production. Regardless of the end product, water removal is necessary and difficult to do cost effectively. For each product the requirements for moisture content (or solids content) vary, such that a desirable water removal strategy would need to be adaptable to varying levels of water removal. Flocculation, with sedimentation and drying was evaluated as a possible strategy for algae dewatering. Anionic and nonionic flocculants are known to be ineffective at flocculating algal culture, which was confirmed for this case by electro-osmotic flow testing of the algae and jar tests with three flocculant charge types. Electrophoretic mobility of the algae indicated that it has a negative charge and no flocs were present in the jars. The effectiveness of the cationic flocculant was determined by measuring settling rates, supernatant turbidity, and filtration rates. Sedimentation and filtration rates of Scenedesmus acutus were measured with varying dosages (0-25 ppm) of a synthetic cationic polymeric flocculant. The results of this study should assist in predicting the time it takes to thicken algae at a concentration range of 0.4-1.0 g/L to a product at a concentration range of 15-250 g/L.

The fields of biodiesel and bioethanol research and development have largely developed independently of one another. Opportunities exist for greater integration of these processes that may result in decreased costs of production for both fuels.To that end, this work addresses the use of the starches and glycerol from processed algal biomass as substrates for fermentation by the yeasts Saccharomyces cerevisiae and Pachysolen tannophilus, respectively. Ethanol producers commonly employ the former yeast for ethanol production and include the latter yeast among candidate species for cellulosic ethanol production.A simple 95% ethanol extraction at 70°C followed by sulfuric acid hydrolysis at 121°C and 2 atm proved a sufficient pretreatment for S. cerevisiae fermentation of starch from Chlamydomonas reinhardtii mutant cw15. The maximum rate of ethanol production was observed as 14 mL/g-h and a maximum concentration of 0.9±0.01% (m/v) was observed by 28 hours. Some starch appeared invulnerable to hydrolysis.P. tannophilus fermentation of glycerol, both independently and among mixed substrates, was likewise demonstrated. It was found that glucose consumption preceded that of glycerol and xylose, but that the latter two substrates were consumed concurrently. Under aerobic, batch conditions, the maximum specific growth rate of the species on a 2% glycerol substrate was observed as 0.04/hr and the yield coefficient for conversion of glycerol to ethanol was 0.07 g/g. While the maximum observed concentration of ethanol in the glycerol-only fermentation was 0.1% m/v, that in mixed media containing 2% each glucose, xylose, and glycerol was 1.5%.Also investigated here was the flocculation of a mutant species of the algae C. reinhardtii by a combination of methanol and calcium. Algae harvest is typically an energy-intensive process, but the technique demonstrated here is not. Complete flocculation of cells was observed with only 5 minutes of mixing and less than 10 minutes of settling using 12 mM CaCl₂ and 4.6% methanol. Ethanol was observed to operate in the same capacity, intimating another area in which yeast bioethanol and algal biodiesel processes might enable one another. During growth, either an inhibitor of flocculation was produced or a facilitator was consumed.

Tendo em vista a potencialidade da remoção de algas utilizando a flotação por ar dissolvido, foi proposto o desenvolvimento de um equipamento de laboratório de fácil operação e manutenção, denominado Floteste, integrando as características geométricas do equipamento Jarteste neste trabalho. Foram realizados ensaios, utilizando água sintética contendo algas da ordem de 108 ind/L e natural proveniente de curso d\'água eutrofizado, possibilitando o aprimoramento do estudo das condições de coagulação, mistura rápida, floculação e flotação. Também, ensaios de flotação seguida de filtração em areia foram feitos visando melhorar a qualidade da água flotada. O jarro do Floteste possui placa de orifícios que proporciona perda de carga suficiente para a distribuição uniforme de água saturada pela seção quadrada do mesmo. Concluiu-se que, principalmente, que a dosagem de coagulante e o respectivo pH de coagulação, tempo e gradiente de velocidade médio de mistura rápida, tempo e gradiente de velocidade médio de floculação, tempo e pressão de saturação e a quantidade de ar fornecido exercem influência significativa na remoção de algas, turbidez, cor verdadeira e do número de partículas nos dois tipos de águas estudadas.
Due to the potentiality of the algae removal by dissolved air flotation, it was proposed the development of an equipment in laboratory scale of easy operation and maintenance, dominated Floteste, integrating the geometric characteristics of the Jarteste equipment in this work. Tests were carried out with synthetic water containing a high concentration of algae (~108 ind/L) and natural water from and eutrophicated source. Besides several improvements in the equipment developed in this study, the rapid mixing can be considered the most important, followed by flocculation and flotation. Also, flotation and sand filtration tests were performed to simulate the floto-filtration technology. The Flotateste vessel have a perforated plate that provides enough loss of load in order to uniform the distribution of saturated water in the bottom. It was concluded, mainly, that the coagulant dose and the pH of coagulation, time and velocity gradient of rapid mixing, time and velocity gradient of flocculation, time and saturation pressure chamber and the amount of air supplied played a significant role in the removal of algae, turbidity, true color and of the number of particles in the two types of water studied.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Novas tecnologias para o tratamento de água vêem sendo desenvolvidas e suas combinações podem apresentar bons resultados principalmente quando submetidas a variações sazonais de origem natural e antropicas. A crescente poluição dos corpos d’água causa florescimentos de algas e cianobactérias nos mananciais, com aparecimento de sabor e odor na água bruta, podendo ocorrer também a liberação de toxinas pelas cianobactérias. Os processos de tratamento de água convencionais têm apresentado deficiências quanto à remoção de cianobactérias e cianotoxinas, principalmente quanto ao aspecto de remoção das células viáveis e na capacidade de remover as toxinas extracelulares. As cianobactérias retidas no lodo dos decantadores representam riscos à qualidade final da água tratada. O presente projeto de pesquisa consistiu em experiência com floco-decantador de manta de lodo acoplado a flotador por ar dissolvido, formando um conjunto composto pelos dois tipos de equipamentos ou tecnologias e ainda com dispositivo limitador de manta. O objetivo da pesquisa foi avaliar o desempenho da instalação proposta quando submetida a variações da qualidade da água bruta, principalmente quando submetido à sobrecarga de algas e cianobactérias, simulando possíveis florações nos mananciais. Os resultados dos ensaios no modulo experimental com água natural apresentaram remoção satisfatória de turbidez , com valores abaixo de 3,0 uT da água floco-floto-decantada e em torno de 0,1 uT da água filtrada. Os ensaios realizados com água natural com presença elevada de algas e cianobactérias, evidenciaram a importância da unidade de flotação, com remoção de clorofila_a de 82% na água decantada/flotada e próximo de 99% na água filtrada, em relação à água bruta, sendo que a turbidez manteve-se abaixo de 3 uT na saída do modulo floco-floto-decantador e a turbidez...
New technologies for water treatment have been developed and their combinations can produce good results especially when subjected to seasonal variations of natural and anthropogenic. The increasing pollution of water bodies causes blooms of algae and cyanobacteria in water sources, with the appearance of taste and odor in raw water, but may also occur the release of toxins by cyanobacteria. The processes of conventional water treatment have shown deficiencies in the removal of cyanobacteria and cyanotoxins, especially on the aspect of removal of viable cells and the ability to remove extracellular toxins. Cyanobacteria retained in the sludge of the sedimentation tanks pose to the final quality of treated water. This research project was to experiment with floc-settling sludge blanket coupled to dissolved air flotation, forming a group composed of two types of equipment or technology, and with relief device blanket. The research aimed to evaluate the performance of the proposed development when subjected to variations in raw water quality, especially when subjected to the overload of algae and cyanobacteria to simulate possible blooms in the springs. The results of tests on an experimental module with natural water showed satisfactory removal of turbidity, with values below 3 uT decanted and around 0,1 uT filtered water. Tests conducted with water with high presence of algae and cyanobacteria, have highlighted the importance of unity flotation Chlorophyll “a” with removal of 82% in the decanted water / rappel and around 99% in filtered water compared to raw water, and the turbidity remained below 3 uT the output of modulo-flake-floto sedimentation and turbidity of filtered water was below 0,6 uT. The limiting device of the ground and periodic removal of sludge, decreased the retention time of the cells retained in the sludge which may have prevented the release of toxins into the water... (Complete abstract click electronic access below)

Orientador: Edson Pereira Tangerino
Banca: Dib Gebara
Banca: Carlos Gomes da Nave Mendes
Resumo: Novas tecnologias para o tratamento de água vêem sendo desenvolvidas e suas combinações podem apresentar bons resultados principalmente quando submetidas a variações sazonais de origem natural e antropicas. A crescente poluição dos corpos d'água causa florescimentos de algas e cianobactérias nos mananciais, com aparecimento de sabor e odor na água bruta, podendo ocorrer também a liberação de toxinas pelas cianobactérias. Os processos de tratamento de água convencionais têm apresentado deficiências quanto à remoção de cianobactérias e cianotoxinas, principalmente quanto ao aspecto de remoção das células viáveis e na capacidade de remover as toxinas extracelulares. As cianobactérias retidas no lodo dos decantadores representam riscos à qualidade final da água tratada. O presente projeto de pesquisa consistiu em experiência com floco-decantador de manta de lodo acoplado a flotador por ar dissolvido, formando um conjunto composto pelos dois tipos de equipamentos ou tecnologias e ainda com dispositivo limitador de manta. O objetivo da pesquisa foi avaliar o desempenho da instalação proposta quando submetida a variações da qualidade da água bruta, principalmente quando submetido à sobrecarga de algas e cianobactérias, simulando possíveis florações nos mananciais. Os resultados dos ensaios no modulo experimental com água natural apresentaram remoção satisfatória de turbidez , com valores abaixo de 3,0 uT da água floco-floto-decantada e em torno de 0,1 uT da água filtrada. Os ensaios realizados com água natural com presença elevada de algas e cianobactérias, evidenciaram a importância da unidade de flotação, com remoção de clorofila_a de 82% na água decantada/flotada e próximo de 99% na água filtrada, em relação à água bruta, sendo que a turbidez manteve-se abaixo de 3 uT na saída do modulo floco-floto-decantador e a turbidez... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: New technologies for water treatment have been developed and their combinations can produce good results especially when subjected to seasonal variations of natural and anthropogenic. The increasing pollution of water bodies causes blooms of algae and cyanobacteria in water sources, with the appearance of taste and odor in raw water, but may also occur the release of toxins by cyanobacteria. The processes of conventional water treatment have shown deficiencies in the removal of cyanobacteria and cyanotoxins, especially on the aspect of removal of viable cells and the ability to remove extracellular toxins. Cyanobacteria retained in the sludge of the sedimentation tanks pose to the final quality of treated water. This research project was to experiment with floc-settling sludge blanket coupled to dissolved air flotation, forming a group composed of two types of equipment or technology, and with relief device blanket. The research aimed to evaluate the performance of the proposed development when subjected to variations in raw water quality, especially when subjected to the overload of algae and cyanobacteria to simulate possible blooms in the springs. The results of tests on an experimental module with natural water showed satisfactory removal of turbidity, with values below 3 uT decanted and around 0,1 uT filtered water. Tests conducted with water with high presence of algae and cyanobacteria, have highlighted the importance of unity flotation Chlorophyll "a" with removal of 82% in the decanted water / rappel and around 99% in filtered water compared to raw water, and the turbidity remained below 3 uT the output of modulo-flake-floto sedimentation and turbidity of filtered water was below 0,6 uT. The limiting device of the ground and periodic removal of sludge, decreased the retention time of the cells retained in the sludge which may have prevented the release of toxins into the water... (Complete abstract click electronic access below)
Mestre

A separação de microrganismos fotossintetizantes no tratamento de efluentes possui dois aspectos fundamentais. O primeiro refere-se à qualidade do efluente tratado e seu impacto sobre os recursos hídricos e, o segundo, refere-se ao potencial deste material como fonte de energia renovável. Diversos trabalhos tem demostrado elevada eficiência na separação de algas no tratamento de efluentes. Entretanto, quando considerado o cultivo de microalgas para utilização da biomassa como matéria prima, para produção de biocombustível por exemplo, mais estudos científicos são necessários. Entre as operações de separação sólido-líquido, normalmente empregadas no tratamento de efluentes, a flotação por ar dissolvido tem se mostrado uma tecnologia vantajosa, pois, além de ser capaz de separar partículas com diâmetro reduzido e baixa velocidade de sedimentação, também permite a obtenção de um material flotado com maior percentual de sólidos, desejável para redução dos custos de processamento da biomassa algal. O objetivo deste trabalho foi avaliar a separação de microalgas cultivadas em uma lagoa de tratamento de esgoto de alta taxa através do processo de coagulação-floculação e flotação por ar dissolvido. Como contribuição aos estudos de separação por FAD, foi avaliado a estabilidade do material flotado submetido a uma agitação mecânica, utilizando a técnica de captura e análise de imagens digitais, segundo um parâmetro chamado porcentagem de área (αa) Este parâmetro é definido como o percentual de pixels pretos em relação ao total de pixels da imagem, e demonstra a instabilidade do material flotado. Os coagulantes cloreto férrico e Tanfloc SG (Tanac®) e os floculantes sintéticos do tipo poliacrilamidas (SNF Floerger®) catiônico (FO4550SH), aniônico (FA920SH) e não iônico (FA920SH) foram investigados em diferentes dosagens e combinações. O presente estudo mostrou que a separação de algas através deste sistema é viável tecnicamente, sendo que os melhores resultados apresentaram uma remoção de turbidez de 92% para a combinação de cloreto férrico (20mg/L) + FO4550SH (2mg/L) e 97% para Tanfloc SG (20mg/L) + AN956SH (1mg/L). Em relação à estabilidade do material flotado, as amostras que continham apenas coagulantes apresentaram valores de αa entre 4,26 e 5,49, indicando uma baixa estabilidade do material flotado. Enquanto as combinações de cloreto férrico (20mg/L) + FO4550SH(0.5mg/L) e Tanfloc SG (20mg/L) +FO4550SH (1 e 2mg/L) foram as que produziram um material flotado com maior estabilidade, apresentando αa=0,35 e αa=0,40, respectivamente, demonstrando que o uso dos polímeros proporciona uma maior estabilidade do material flotado, quando este está sujeito a turbulências.
Separation of photosynthetic microorganisms in the effluent treatment has two fundamental aspects. The first refers to the quality of the treated effluent and its impact on water resources, and the second refers to the potential of this material as a source of renewable energy. Several studies show high efficiency in the separation of algae in effluent treatment. However, more scientific studies are required considering the cultivation of microalgae for the use of them as a raw material for biomass, like biofuel for instance. Among solid-liquid separation operations normally employed in effluents treatment, dissolved air flotation has been shown to be an advantageous technology in order to separate algae, because allows not only the separation of particles with reduced diameter and low sedimentation velocity, but also produces a floating material with higher percentage of solids, which is desirable for reducing the processing costs of the algal biomass. The aim of this work was to evaluate the separation of microalgae originated on a high rate pond through the coagulation, flocculation and dissolved air flotation (DAF) processes. As a contribution to the DAF separation studies, the stability of the floating material was evaluated against mechanical agitation, using the technique of digital image analysis, according to a parameter called area percentage (αa) This parameter is defined as the percentage of pixels in relation to the total pixels of the image, and demonstrates the instability of the floating material. The ferric chloride and Tanfloc SG (Tanac®) coagulants and the synthetic flocculants polyacrylamide types (SNF Floerger®) cationic (FO4550SH), anionic (FA920SH) and nonionic (FA920SH) were investigated in different concentrations and combinations. The present study showed that algae separation through this system is technically feasible. The best results showed a turbidity removal of 92% for the combination of ferric chloride (20mg/L) + FO4550SH (2mg/L) and 97% for Tanfloc SG (20mg/ L) + AN956SH (1mg/L). In relation to the stability of the floated material, the samples containing only coagulants presented values of αa between 4.26 and 5.49, indicating a low stability of the floated material. While the ferric chloride (20mg / L) + FO4550SH (0.5mg / L) and Tanfloc SG (20mg / L) + FO4550SH (1 and 2mg / L) combinations were the ones that produced a floated material with greater stability, 0.35 and α = 0.40, respectively, demonstrating that the use of the polymers provides greater stability of the floated material when it is subjected to turbulence.

Microalgae are a diverse group of oxygenic photosynthetic microorganisms which show great promise as a source of biofuel. However, significant challenges still remain before microalgae can be considered a viable source of biofuel. The main current challenges are nutrient sourcing and recycling as well as downstream processing. The algal cell wall and especially the presence of an algaenan cell wall in some Chlorophyte algae could be an important variable in determining downstream processing costs but not much comparative research has been done to elucidate this. The first part of the present study focuses on the recently isolated alga Pseudochoricystis ellipsoidea (Trebouxiophyceae) and its improvement and assessment for biofuel production. Random mutagenesis and FACS screening protocols were developed for the isolation of pigment and cell wall mutants but despite considerable efforts no suitable mutants could be identified in the first half of this project. Two 500 L raceway ponds as well as an algal growth room and bubble column bioreactors were set up to facilitate algal research at the University of Bath and assess the performance of P. ellipsoidea in realistic culture conditions. P. ellipsoidea showed a maximum growth of 1.53 divisions day-1 in semi-open raceway ponds, resistance to contamination and a 30% lipid content, making it particularly suitable for raceway pond cultures. In the second part of this project six species of Chlorophyte (“green”) algae, three of which produced algaenan, were compared for suitability to growth in anaerobic digestate and municipal wastewater as well as cell wall strength, permeability and suitability to hydrothermal liquefaction. We found that anaerobic digestate was a good medium for the growth of all species independently of autoclaving and that non-autoclaved wastewater was a very challenging medium. Algaenan production did not affect cell disruption by ultrasonication but growth stage and cell wall thickness did. Lipid extraction kinetics by chloroform/methanol were greatly affected by algaenan, meaning that this material is relatively impermeable to organic solvents. Cell wall thickness, cell volume and lipid content also had an effect on lipid extraction kinetics but this was only measurable after 180 minutes of extraction. 8 Hydrothermal liquefaction showed high solid and low oil yields, very low sulphur (≤0.1 %) as well as a 1.1 % -1.8 % nitrogen content which is significantly lower than most algal HTL studies to date. This suggests that stationary stage algae are more difficult to process but give a cleaner biocrude and reduce the loss of nitrogen through incorporation in the oil. Significant opportunities for optimisation still exist in the HTL process.

The phenomenon of rapid algal blooms in response to nutrient overloads has been adapted to treat synthetic domestic wastewater. Various algal consortia collected from several eutrophied water bodies were subject to high density algal culture (upto 106-107 cells/mL) and screened for rapid algal growth, pollutant removal, nutrient recovery under mixotrophy and auto-flocculation. When tried in laboratory scale algal ponds, these algal consortia showed growth rates between 0.15 and 1.07 d-1. Results indicate that Chlorella occurred frequently among most consortia although not always the largest in number. While individual algal species varied in growth rates among these consortia, the log phase for most of these algae lasted 4-5 d after which the algal species began to flocculate between day 5-8 at different rates. The flocculation stage lasted between Day 6-8 wherein about 65% cells flocculated during monsoon and over 90% in winter. Although over 90% removal of N and 80% removal of P occurred in this period, the net N and P harvested as flocculated algae ranged from ~30-50% and ~40-70%, respectively. A consortia approach, wherein algal cells auto-flocculate after reaching a high cell density and nutrient removal provides an easy, low energy and sustainable approach to simultaneous wastewater treatment as well as energy and nutrient recovery from domestic wastewaters.

The phenomenon of rapid algal blooms in response to nutrient overloads has been adapted to treat synthetic domestic wastewater. Various algal consortia collected from several eutrophied water bodies were subject to high density algal culture (upto 106-107 cells/mL) and screened for rapid algal growth, pollutant removal, nutrient recovery under mixotrophy and auto-flocculation. When tried in laboratory scale algal ponds, these algal consortia showed growth rates between 0.15 and 1.07 d-1. Results indicate that Chlorella occurred frequently among most consortia although not always the largest in number. While individual algal species varied in growth rates among these consortia, the log phase for most of these algae lasted 4-5 d after which the algal species began to flocculate between day 5-8 at different rates. The flocculation stage lasted between Day 6-8 wherein about 65% cells flocculated during monsoon and over 90% in winter. Although over 90% removal of N and 80% removal of P occurred in this period, the net N and P harvested as flocculated algae ranged from ~30-50% and ~40-70%, respectively. A consortia approach, wherein algal cells auto-flocculate after reaching a high cell density and nutrient removal provides an easy, low energy and sustainable approach to simultaneous wastewater treatment as well as energy and nutrient recovery from domestic wastewaters.

High rate algal ponds (HRAPs) can be utilised as an efficient and economical wastewater treatment method while also producing algal biomass. This study focused on the use of HRAPs to assimilate nutrients from secondary lagoon effluent and investigated various methods in which to enhance the algal biomass productivity of the HRAPs. The natural operation, productive potential, biomass production, nutrient removal capacity and environmental conditions were observed. From these findings, three experiments were proposed to enhance biomass production and in turn, the nutrient removal of the HRAPs. The first experiment was the addition of three separate algal cultures to the HRAPs during winter. Two of the algal species enhanced biomass production, however, there was no significant difference in nutrient removal during any of these experiments. The second set of experiments controlled the pH of the HRAPs utilising an inorganic and organic acid to determine if it was solely the control of pH which enhanced biomass production or if the addition of carbon that played a significant role. It was found that under high algal productivity conditions utilising inorganic acid to control pH negatively impacted algal growth whereas utilising organic acid significantly enhanced algal growth. The third experiment compared secondary lagoon effluent and primary lagoon effluent as the media sources. Secondary lagoon effluent was found to have higher biomass productivity by 106mg/L. This was thought to be a result of the primary lagoon effluents high colloidal turbidity. The results from the biomass enhancement experiments alongside the natural operation of the HRAPs were utilised to develop a simple and accurate algal growth model which utilised readily available data. The model aims to determine the biomass production of HRAPs in the south-eastern Australian climate which operated under elevated pH levels. The model was validated against the use of both secondary and primary lagoon effluent in the HRAPs and returned an R-squared value 0.98, suggesting a high accuracy. Following this work, two algal harvesting methods were investigated; membrane filtration and fungal flocculation. Three different membrane filtration systems were trialled and compared; ceramic crossflow system, polytetrafluoroethylene (PTFE) submerged system and a metal crossflow system. The PTFE membrane was found to be the most effective of the membranes tested for harvesting algae due to its low fouling tendency, low cost and relatively constant flux. The flocculation capability of fungi to flocculate algae was examined. Aspergillus oryzae was found to be the most effective fungi species trialled for monoculture flocculation with over 95% removal for all algal species tested. The fungal flocculation of mixed algal communities in wastewater samples was also investigated and removal values of 70-100% were achieved. Overall, the work conducted provides valuable information on the operation and enhancement of HRAPs. Furthermore, the simple model developed can be utilised to help identify the potential of an area for algal biomass production and the feasibility of incorporating HRAP systems into an existing wastewater treatment facility. The two harvesting techniques trialled offer new and vital insight into the often-difficult process of algal harvesting.

Due to eutrophication of aquatic environment, massive growth of algae and cyanobacteria occurs and the seasonal algal bloom is formed. Drinking water treatment plants have to deal with the increased amount of cells as well as organic compounds produced by algae and cyanobacteria (so-called AOM). Moreover, the presence of AOM causes a reduction in the efficiency of coagulation, which is an essential process in drinking water treatment. To increase coagulation efficiency, supportive methods, such as ozone oxidation, are added usually prior to coagulation. While many studies focused on the ozonation of algal and cyanobacterial cells, little is known about the effect of ozonation on AOM. This diploma thesis focused on the evaluation of the effect of ozonation in combination with coagulation on the removal of cellular organic compounds (COM) produced by cyanobacteria Microcystis aeruginosa. The effect of ozonation before or after coagulation on COM removal was investigated. The degradation of microcystins, which are naturally contained in the COM sample, was also monitored. Various ozone doses (1 - 10 mg/L) were tested at three pH values - 5, 7 and 9. Two coagulants were utilized - aluminium sulphate and ferric sulphate. Ozonation removed COM negligibly. However, eliminated microcystins, the degradation...

Recent progress in algae biotechnology indicates that microalgae have the potential of becoming a significant source for food, feed proteins, nutraceuticals, and lipids for biofuels. Typically low concentrations of microalgae cultures (less than 2 g/L) make harvesting of algae biomass one of the key economic bottlenecks for microalgae production of biofuels and bioproducts. Among the various biomass harvesting options currently under consideration, flocculation appears to be the least expensive and most flexible method for harvesting and initial concentration of dilute algal cultures. In addition to initial biomass concentration, processing factors that could also affect harvesting efficiency include culture pH, flocculant dosage, and media ionic strength (conductivity). This thesis reviews challenges of harvesting and concentration of green microalgae and examines the effect of pH, flocculant dosage, and culture conductivity on charge neutralization and flocculation of Nannochloris oculata by aluminum chloride. N. oculata flocculation was studied by manipulating the culture pH and ionic strength before the addition of aluminum chloride. The removal efficiency, concentration factor, settling rate, and zeta potential of the culture were measured to assess the effect of processing variables and understand mechanisms that govern N. oculata flocculation by aluminum chloride. Flocculation tests conducted with culture concentrations of 10^7 cells/ml revealed that AlCl3 concentration of 0.05 g/L and flocculation pH of 5.3 were optimal conditions for achieving 100% removal efficiency and a twentyfold algae concentration. At flocculant concentrations greater than 0.05 g/L, removal efficiencies were equally good but resulting concentration factors decreased with increasing AlCl3 dosage. Zeta potential measurements were correlated with flocculation dosage, initial cell concentration, medium pH, and aluminum solubility curves to conclude that densely charged multi-valent aluminum hydroxide species were responsible for the efficient flocculation at pH 5.3 with 0.05 g/L AlCl3.