Tesis sobre el tema "Cr (VI) reduction"

In  this  study,  tolerance  of  soil  bacteria  to  hexavalent  chromium  (Cr(VI))  was  investigated.  First,  influence  of  high chromium levels of anthropogenic and geogenic origin on the  soil cultivable  bacterial community was examined. Next, a number  of  bacterial  strains  with  high  Cr(VI)  tolerance  were  isolated  from  diverse   environmental  samples  such  as  soil, sediment, water and waste material.  Strains were  identified  and  tested for  the  level of  Cr(VI) tolerance  and  the  ability toreduce toxic Cr(VI) to more innocuous Cr(III). Selected  Bacillus cereus  group strains  were further characterized  -  their morphological  and  biochemical  characteristics,  16S  rRNA  and  pycA  gene  sequences,  biofilm  formation  potential  and resistance to other heavy metals were determined. Also, more detailed study of their tolerance level and  Cr(VI) reduction was  conducted.  Strain  with  the highest  resistance  together  with the  control  chromate  sensitive  strain  were  analyzed  by STEM EDS for their cellular and endospore Cr content under different conditions. Results indicate Cr(VI) tolerant bacteria are  present  both  in  low  and  high  Cr  environments.  Majority  of  isolates  belonged  to  the  B.  cereus  group  indicating  its overall high tolerance to  Cr(VI). Certain strains exhibited high  tolerance and reduction  ability,  indicating their possibleusefulness  in practical  bioremediation  application.  STEM  EDS  analysis  of  Cr(VI)-sensitive  B.  subtilis  PY79  strain  and Cr(VI)-resistant  B. cereus  group strain  NCr1a revealed  significant differences in their response to Cr(VI)  and in  their  Cr cellular and endospore content.
U ovom radu ispitana je tolerantnost  zemljišnih  bakterija na šestovalentni hrom (Cr(VI)). Prvo, ispitan je uticaj visokog nivoa  hroma  antropogenog  i  geogenog  porekla  na  kultivabilnu  bakterijsku  zajednicu  zemljišta.  Dalje,  izolovani  su bakterijski sojevi sa visokom tolerancijom na Cr(VI) iz različitih sredinskih uzoraka   kao što su zemljište, sediment, voda i otpadni materijal. Sojevi su identifikovani i određen je nivo njihove Cr(VI) tolerancije i sposobnost redukcije toksičnog Cr(VI)  u  manje  toksični  Cr(III).  Odabrani  sojevi  Bacillus  cereus  grupe  su  dalje  karakterisani  –  određene  su  njihove morfološke i biohemijske karakteristike, 16S rDNK i  pycA  sekvence, potencijal formiranja biofilma i otpornost na druge teške  metale.  Takođe,  sprovedeno  je  detaljnije  ispitivanje  njihove  tolerancije  i  redukcije  Cr(VI).  Soj  sa  najvišom otpornošću  je  uporedo  sa  kontrolnim  osetljivim  sojem  analiziran  pomoću  STEM  EDS  na  sadržaj  hroma  u  ćelijama  I endosporama u različitim uslovima. Rezultati ukazuju da su bakterije tolerantne na Cr(VI) prisutne i u sredinama sa niskim i  sa  visokim  koncentracijama  hroma.  Većina  izolata  pripadala  je  B.  cereus  grupi  što  ukazuje  na njenu  uopšteno  visoku otpornost na Cr(VI). Pojedini sojevi su pokazali visoku otpornost i sposobnost  redukcije Cr(VI), što ukazuje na mogućnost njihove praktične primene u bioremedijaciji. STEM EDS analiza osetljivog B. subtilis PY79 soja i Cr(VI)- rezistentnog soja B.  cereus  grupe  NCr1a  otkrila  je  značajne  razlike  u  njihovom  odgovoru na  Cr(VI)  i  sadržaju  Cr  u njihovim  ćelijama  i endosporama.

Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are often present together at contaminated sites. These sites are considered difficult to clean-up using bioremediation technologies because of the toxicity of heavy metals to microorganisms. Laboratory experiments were conducted to verify if biodegradation of a model PAH, naphthalene, could be sustained over a long time-period (weeks) in the presence of a common heavy metal contaminant, Cr (VI). Complete reduction of Cr (VI) at concentrations up to 6.3 mg/L was achieved by Pseudomonas putida ATCC 17484 in the presence of naphthalene that was continuously released from an immiscible organic liquid, 2,2,4,4,6,8,8-heptamethylnonane (HMN). The presence of Cr (VI) inhibited bacterial growth and reduced naphthalene biodegradation rates. Despite this the microorganisms were able to degrade significant masses of naphthalene, quantities much greater than those reported in earlier studies. The addition of 1,2-Naphthoquinone, a possible by-product of naphthalene degradation and an oxidizing agent, resulted in improved naphthalene biodegradation rates in the presence of Cr (VI).

An indigenous mixed culture of bacteria collected from a Wastewater Treatment Plant (Brits, North West Province, South Africa), biocatalytically reduced Cr(VI) in the presence of As(III). Both the reduced chromium (Cr(III)) and the oxidised arsenic (As(V)) readily form amorphous hydroxides that can be easily separated or precipitated from the aqueous phase as part of the treatment process. Treatment of Cr(VI) and As(III) before disposal of wastewater is critical since both compounds are known to be carcinogenic and mutagenic at very low concentrations, and acutely toxic at high concentrations. Batch experiments were conducted to evaluate the rate of Cr(VI) reduction under anaerobic condition in the presence of its co-contaminant As(III) typically found in the groundwater and mining effluent. Results showed near complete Cr(VI) reduction under initial Cr(VI) concentrations up to 70 mg/L in a batch amended with 20 mg/L As(III). However, increasing Cr(VI) concentrations up to 100 mg/L resulted in the inhibition of Cr(VI) reduction activity. Further investigation was conducted in a batch reactor amended with 70 mg/L Cr(VI) concentration at different As(III) concentrations ranging from 5-70 mg/L to evaluate the effect of varying As(III) concentration on Cr(VI) reduction efficiency. Results showed that Cr(VI) reduction efficiency increased as As(III) concentrations increased from 5-40 mg/L. However, further increase in As(III) concentration up to 50 mg/L resulted in incomplete Cr(VI) reduction and decrease in Cr(VI) reduction efficiency. These results suggest that the rate of Cr(VI) reduction depends on the redox reaction of As(III) and As(V) with Cr(VI). Moreover, the inhibitory effect observed at high Cr(VI) and As(III) concentration may also be attributed to the dual toxicity effect of Cr(VI) and As(III) on microbial cell. From the above batch kinetic studies lethal concentration of Cr(VI) and As(III) for these strains was evaluated and established. Initial evaluation of the bacteria using 16S rRNA partial sequence method showed that cells in the mixed culture comprised predominantly of the Gram-positive species: Staphylococcus sp., Enterobacter sp., and Bacillus sp. The biokinetic parameters of these strains were estimated using a non-competitive inhibition model with a computer programme for simulation of the Aquatic System “AQUASIM 2.0”. Microbial reduction of Cr(VI) in the presence of As(III) was further investigated in continuous-flow bioreactors (biofilm reactor) under varying Cr(VI) loading rates. The reactor achieved Cr(VI) removal efficiency of more than 96 % in the first three phases of continuous operation at lower Cr(VI) concentration ranging from 20-50 mg/L. However, 20 % decrease in Cr(VI) removal efficiency was observed as Cr(VI) concentration increase up to 100 mg/L. The reactor was able to recover from Cr(VI) and As(III) overloading phase after establishing the resilient nature of the microorganism. Similarly to the batch reactor studies the overall performance of the reactor also demonstrated that the presence of As(III) greatly enhance Cr(VI) reduction in a bioreactor. This was evident by near complete removal of Cr(VI) concentration up to 50 mg/L. The basic mass balance expressions on Cr(VI) along with the non-competitive inhibition model were used to estimate the biokinetic parameters in the continuous flow bioreactor system. Cr(VI) reduction efficiency along the longitudinal column was also evaluated in this study. Results showed that Cr(VI) efficiency increased as Cr(VI) concentration travels along the longitudinal column. Other important factors such as oxygen and pH during biological Cr(VI) reduction in the presence of As(III) oxidation were also evaluated.
Dissertation (MEng)--University of Pretoria, 2014.
tm2015
Chemical Engineering
MEng
Unrestricted

Šiame eksperimente buvo nagrinėjama pH įtaka Cr (VI) ir Cu (II) jonų pašalinimui iš vandeninių tirpalų, naudojant metalinę geležį Fe (0), kai tirpalų pH vertės buvo nuo 2 iki 6, purtymo procese, uždaruose ir atviruose induose. Kadangi Cr (VI) ir Cu (II) jonų koncentracijų sumažėjimas tirpale priklauso nuo geležies paviršiaus, tai labai svarbu ją tinkamai paruošti: išvalyti ir aktyvuoti. Maksimalus Cr (VI) jonų pašalinimo efektyvumas buvo esant pH vertei 2, o Cu (II) jonų atveju, kai pH vertė 4 uždaruose induose ir atviruose induose – chromo atveju pH 6, vario atveju, kai pH 4. Pašalinimo įvertinimui naudojamos kalibraciniės kreivės pagal kurias apskaičiuojamos likusiųjų jonų koncentracijos, matuojant tirpalų optinius tankius. Metodas yra pigus ir patikimas, nes pašalinima didelė dalis sunkiųjų metalų jonų.
The effects of pH on Cr (VI) and Cu (II) ions removal from solutions by Fe (0) was investigated by batch shaking process. Since the presence of ferrous iron in the solution is mainly responsible for Cr (VI) and Cu (II) reduction the surface of iron must be purified and activated. The maximum Cr (VI) removal efficiency was found at pH 2 and in Cu (II) case it was pH 4 without oxygen and in case with open jar it was for Cr (vi) removal pH 6 and for Cu (II) removal pH 4. Remained concentrations of Cu (II) and Cr (VI) ions were investigated using calibrated graphs and analysis of optical density. This study confirmed that this method is cheap because we can use wasted iron and effective of removing most of heavy metal ions from solutions.

Thesis (M.S.)--East Tennessee State University, 2004.
Title from electronic submission form. ETSU ETD database URN: etd-1110104-211520 Includes bibliographical references. Also available via Internet at the UMI web site.

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Fundação Araucária
This work aims to study the reduction of hexavalent chromium to trivalent form through the adsorption process as assessed by the Kβ X-ray emission spectrometry. As adsorbent material activated carbon samples were used, while the resin Amberlite IR 120 was used as an indicator of the presence of Cr(III) in all solutions containing Cr(VI). Preliminar speciation tests were performed previously in solutions containing Cr(VI) in order to analyze the possible reduction to Cr(III) due to the effect of solution pH. A EDTA-based colorimetric speciation method of Cr(III) was applied. Preliminary kinetic Cr adsorption tests were performed at controlled temperature and agitation, achieving the equilibrium at 24 h for activated carbon. Batch single equilibrium Cr adsorption experiments using activated carbon and cation exchange resin materials as adsorbents and 8 mequiv.L-1 of Cr (III) and Cr(VI) ions as adsorvates were performed at pH 3.5 and under controlled temperature and agitation. Adsorbent and Cr reference material samples were pressed in pellets for spectrometric analysis. By using a high-resolution spectrometer of Johann type and a 6.1 keV monochromatic X-ray beam, Kβ X-ray emission spectra of Cr-treated adsorbent and reference material samples were registered by a Si detector, scanning the scattering X-ray by a spherycal bent analyzer around the Kβ1,3 spectral line of metallic chromium. The sample, spherical bent analyzer and detector system was positioned on the Rowland circle in order to scan in high resolution condition, focus the maximum back-scattered X-ray beam on the main detector and built Kβ X-ray emission spectra. As the incident monochromatic X-ray beam is a time-depending function, X-ray intensity that was registrated by detector was monitored and it was normalized to monitor-detector intensity. By setting measurement time of 2-4 h for Cr-treated adsorbent samples and 10-30 min for Cr reference material ones, a complete full scan of Kβ X-ray emission region was performed with enough statistic to observe the sattelite lines of chromium, which suffer a strong influence due to the oxidation state of metal ion and the chemical environment. The Cr-Kβ emission spectra were plotted on the basis of recorded X-ray intensity (y-axis) and spherical bent analyzer (SBA) position (x-axis), performing both the monitor-to-normalized intensity and the converted-to-energy SBA position. Besides this, scattered X-rays on matrix bulk and chromium absorption edge effect were systematically subtracted from Cr-Kβ emission spectra, applying pseudo-physical procedures and consequentely allowing enhancing the weaker sattellites lines of chromium. Main physical characteristic such as energy and intensity of main (Cr-Kβ1,3) and satellite lines (Cr-Kβ2,5 and Cr-Kβ ) for Cr-Kβ emission spectra of Cr treated-adsorbent samples were extracted by gaussian type peak fits and then compared with those of Cr reference materials, allowing to assign the oxidation state of chromium ions adsorbed on activated carbon surface and removed by an ion exchange process on cationic resin surface. In addition, no Cr(VI) reduction in acidic solutions was observed according to the EDTA-based colorimetric speciation result as well as with no presence of Cr(III)-Kβ spectral line pattern in Cr(VI) treated cationic resin samples. Based on Cr-Kβ spectral line analysis, the activated carbon samples treated with Cr(III) and Cr(VI) ions have shown the same spectral line pattern corresponding to the Cr(III) one. Thus, the reduction of Cr(VI) to Cr(III) has occurred by the adsorption process
Este trabalho visa estudar a redução do cromo hexavalente à forma trivalente através do processo de adsorção, avaliada pela espectrometria Kβ de emissão. Amostras de carvão ativado foram utilizados como material adsorvente, enquanto a resina Amberlite IR 120 foi usada como um indicador da presença de Cr(III) em todas as soluções contendo Cr(VI). Testes preliminares de especiação foram realizados em soluções contendo Cr(VI), a fim de analisar a possível redução para Cr(III) devido ao efeito do pH da solução. Foi aplicado o método de especiação colorimétrica de Cr(III), usando como complexante o EDTA. Testes preliminares da cinética de adsorção de íons de Cr foram realizados em batelada a temperatura e agitação controlada, alcançando o equilíbrio em 24 h para o carvão ativado. Foram realizados experimentos de adsorção de Cr utilizando carvão ativado e resina de troca catiônica materiais em soluções contendo 8 mequiv L-1 de Cr(III) e Cr(VI) em pH 3,5 e com temperatura e agitação controladas. Foram prensados, em forma de pastilhas, amostras de adsorventes tratados com Cr(III) e (VI), além de materiais de referência de Cr, para análise espectrométrica. Usando um espectrômetro de alta resolução do tipo de Johann e um feixe de raios X monocromático de 6,1 keV, foram registrados, por um detector de Si, espectros de emissão de raios-X Kβ de amostras de material adsorbente tratados com íons de Cr bem como de materiais de referência, fazendo para tanto a varredura em energia dos raios-X espalhados pela amostra em torno da linha espectral principal Kβ do cromo metálico. O conjunto amostra, analisador esfericamente curvado (SBA) e detector foi posicionado sobre um círculo de Rowland, a fim de obter, em condições de alta resolução, a focalização do feixe de raios X retro-espalhados no detector principal e permitindo a construção de espectros de emissão Kβ. Como a intensidade do feixe incidente de raios-X monocromático foi uma função dependente do tempo, a intensidade de raios-X registrada pelo detector foi monitorada e normalizada por aquela registrada pelo detector-monitor. Ao definir o tempo de medição de 2-4 h para amostras adsorvente tratadas com íons de Cr e 10-30 min para os compostos de referência de Cr, uma região completa do espectro de emissão de raios-X foi obtida com estatística suficiente para observar as linhas satélite dos íons de cromo, que sofrem uma forte influência devido ao estado de oxidação do íon metálico e do ambiente químico. Os espectros Kβ foram graficados em intensidade de raios-X contra a posição do analisador curvado (SBA), sendo sistematicamente normalizados a intensidade do detector-monitor e convertendo a posição do SBA em energia. Além disso, o fundo oriundo dos raios X espalhados na amostra e do efeito da borda de absorção do Cr foi subtraído de todos os espectros de emissão Cr-K, destacando assim as linhas satelites de cromo. As características físicas, como a energia e a intensidade, das linhas principais (Cr-Kβ1,3) e linhas satélite (Cr-Kβ2,5 e Cr-Kβ") foram extraídas dos espectros de emissão Cr-K das amostras tratadas com Cr e comparados com os dos materiais de referência, permitindo inferir o estado de oxidação do cromo adsorvido no carvão ativado e os que também foram removidos pela resina catiônica. Além disso, não foi observado a redução do Cr(VI) na solução, de acordo com a ausência das linhas espectrais de Cr(III) em amostras de resina catiônica tratadas com Cr(VI). Baseado na análise das linhas espectrais, as amostras de carvão ativado tratadas com Cr(III) e Cr(VI) têm mostrado o mesmo padrão de linhas espectrais correspondentes ao Cr(III) e portanto, a redução de Cr(VI) para Cr(III) ocorreu durante o processo de adsorção

碩士
東海大學
環境科學與工程學系
99
Photocatalytic reduction of Cr(VI) were performed at different solution pH on nanosize TiO2(Degussa P25), then residual hexavalent chromium in liquid phase and P25 solid were separated and each was studied using X-ray absorption spectroscopy,UV-Vis spectrophotometry, X-ray powder diffraction, scanning electron microscopy and BET surface analyzer. The results indicated that the highest photocatalytic reduction activity was obtained at pH 4. XAS results showed that the chromium in both liquid phase and solid phase was trivalent. The coordination structure around Ti (Debye-Waller factor 2 and coordination number N) after photocatalytic reduction Were unchanged. No incorporation of chromium into TiO2 lattice was observed. Photocatalytic reduction of an industrial wastewater (pH 7.67) containing hexavalent chromium and 1.28 mg L-1 TOC on P25 was more effective than that of the Cr(VI)-containing water (pH 7) synthesized in our laboratory. This was because the 1.28 mg/L TOC in the industrial wastewater could promote photocatalytic reduction of Cr(VI).

碩士
國立臺灣科技大學
化學工程系
102
In this study, the photoelectrocatalytic reactor constructed by the structure design of batch reactor was used for the photoelectrocatalytic reduction of hexavalent chromium (Cr(VI)) in aqueous phase. The photocatalytic properties of photocathodes with different TiO2 thickness are examined. The experimental results indicated that the 6.50 μm thickness of TiO2 film shows the highest photocatalytic activity among all the thickness investigated. The effects of solution pH, light intensity, initial Cr(VI) concentration, periodic illumination, bias potential and driving modes of bias potential were investigated on the photocatalytic and photoelectrocatalytic processes. The kinetics parameters of photocatalytic reduction of aqueous Cr(VI) was studied and discussed. The photocatalytic reduction of Cr(VI) for experiments conducted with periodic illumination were higher than that conducted with continuous illumination at pH 2. Because the surface fractional coverage is higher than replenished surface coverage of concentration of hydroxide and oxygen during long illumination period. Therefore, the photocatalytic reduction of Cr(VI) became slower at the long illumination period. The extent of electrolytic reduction was increased with decreasing applied bias potential. The bigger negative value of bias potential which provided more electron to reduce Cr(VI). Reduction of aqueous Cr(VI) was efficiently enhanced by photoelectrocatalytic process because the photoinduced electrons efficiently accumulate on TiO2-coated photocathode. The driving mode of half-rectified square wave mode (HR-SW) for electrolytic reduction also was investigated. However, the reduction of Cr(VI) under HR-SW mode was lower than which with constant DC mode when the negative bias potential. It is considered that when turning the bias potential from negative value to zero, the electrons which accumulating on the surface of cathode are drown to anode via external circuit under HR-SW mode.

South Africa currently faces multiple Cr(VI) contamination problems which are unsuccessfully remediated using available technologies. Cr(VI) is highly toxic, carcinogenic and mutagenic in nature and it is exclusively released through anthropogenic activities. A new treatment approach is proposed using locally isolated Cr(VI) reducing species of bacteria. This method is envisioned to be economical and ecologically friendly. Indigenous chromium(VI) reducing bacteria (CRBs) were isolated from a dried sludge consortium collected in the Brits Wastewater Treatment Plant, North-West Province (South Africa). Characterisation using 16S rRNA fingerprinting followed by taxonomic studies revealed a wide diversity of CRBs isolated under anaerobic conditions than under aerobic conditions. The consortium was determined to be predominantly gram-positive. The Cr(VI) reducing component of the culture was determined to be predominantly facultative, consisting predominantly of Bacillus sp., i.e. B. cereus, B. thuringiensis and B. mycoides. Batch experiments under both aerobic and anaerobic conditions showed a high Cr(VI) reducing performance under relatively high initial Cr(VI) concentrations. The reduction rate using this culture was 3 to 8 times higher than reduction rates reported in bacteria previously isolated and studied in North America and Europe. The culture performed best as a consortium with the different species operating cooperatively. The bacteria were acclimated to Cr(VI) toxicity through the long period of contact during the activated sludge treatment process at the source. A Monod like model was used to evaluate the rate of Cr(VI) reduction over a wide range of initial Cr(VI) concentrations. The model revealed that Cr(VI) reduction in the consortium culture followed quasi-first order kinetics with a Cr(VI) inhibitor term as a second exponential: C = C0 . exp [-p . exp (-q . C0 ) . t]. The parameter p and q for the semi-empirical first order model were statistically accurate with R2 values greater than 94% for all data ranges evaluated. Previous studies were not able to pick the variability of Monod coefficients, kmc and Kc, since at narrow ranges of initial Cr(VI) concentrations, the impact of the chromium toxicity variability was insignificant. This study demonstrates the potential of a biological approach using locally isolated Cr(VI) reducing bacteria to decontaminate Cr(VI) polluted sites in South Africa.
Dissertation (MSc)--University of Pretoria, 2009.
Chemical Engineering
unrestricted

碩士
嘉南藥理大學
環境工程與科學系
102
In recent years, many researcheshave confirmed the positiveresultson photo-catalytic degradation of environmental pollutants.In this study,titania (Degussa, P25) has been applied tophoto-catalytic reduction of hexavalent chromium in aqueous solution, which could discuss the effect of UV photo-catalytic under titanium dioxide by different hole scavengers, and the impact of hexavalent chromiumreduction. This study has controlledvarious conditions in order to reach the optimal results of chromium reduction,including different intensities of UV light, different pH values and differentconcentrations of photo-catalyst, various hole scavengers, and hexavalent chromium. The results indicated that the best effect on the hexavalent chromium reductionwas at photo-catalytic reaction conditions under 30mmolof titanium dioxide, 0.1mmol citric acid as hole scavenger, pH = 3, 1: 300 as the ratio of citric and a titanium dioxide,and 0.34mW/cm2 as the light intensity, whilethe hexavalent chromium was 0.04mmol in water,where the hexavalent chromium was complete reduced in 40 minutes. Moreover,the other important experimental results have confirmed some reactive conditions as below: The better effect of the hexavalent chromium reduction was accomplished whilethe increase of the light intensity.The worse result under sodiumsalt type hole scavenger as trapping agent was observed.The higher numbers of carboxyl functional group as hole scavenger illustrated better hexavalent chromium reduction.The best effect of the hexavalent chromium reduction was reached at the concentration of the titanium dioxidewas30mmol, where the reduction effect gradually decreased while the concentration of titanium dioxide higher or less than30mmol.

Chromium (VI) is a pervasive groundwater contaminant that poses a considerable threat to human health. Remediation techniques have focused on the reduction of the highly mobile Cr(VI) to the sparingly soluble, and less toxic, Cr(III) species. Traditionally, remediation performance has been evaluated through the measurement of Cr(VI) concentrations; however, this method is both costly and time-consuming, and provides little information regarding the mechanism of Cr(VI) removal. More recently, Cr isotope analysis has been proposed as a tool for tracking Cr(VI) migration in groundwater. Redox processes have been shown to produce significant Cr isotope fractionation, where enrichment in the ⁵³Cr/⁵²Cr ratio in the remaining Cr(VI) pool is indicative of a mass-transfer process. This thesis describes laboratory batch and column experiments that evaluate the Cr isotope fractionation associated with the reduction of Cr(VI) by various materials and under various conditions. Laboratory batch experiments were conducted to characterize the isotope fractionation during Cr(VI) reduction by granular zero-valent iron (ZVI) and organic carbon (OC). A decrease in Cr(VI) concentrations was accompanied by an increase in δ⁵³Cr values for the ZVI experiments. Data were fitted to a Rayleigh-type curve, which produced a fractionation factor α = 0.9994, suggesting a sorption-dominated removal mechanism. Scanning electron microscopy (SEM), X-ray absorption near-edge structure (XANES) spectroscopy, and X-ray photoelectron spectroscopy (XPS) indicated the presence of Cr(III) on the solid material, suggesting that reduction of Cr(VI) occurred. A series of batch experiments determined that reaction rate, experimental design, and pre-treatment of the ZVI had little to no effect on the Cr isotope fractionation. The interpretation of isotope results for the organic carbon experiments was complicated by the presence of both Cr(VI) and Cr(III) co-existing in solution, suggesting that further testing is required. A laboratory column experiment was conducted to evaluate isotopic fractionation of Cr during Cr(VI) reduction by OC under saturated flow conditions. Although decreasing dissolved Cr(VI) concentrations also were accompanied by an increase in δ⁵³Cr values, the isotope ratio values did not fit a Rayleigh-type fractionation curve. Instead, the data followed a linear regression equation yielding α = 0.9979. Solid-phase analysis indicated the presence of Cr(III) on the surface of the OC. Both the results of the solid-phase Cr and isotope analyses suggest a combination of Cr(VI) reduction mechanisms, including reduction in solution, and sorption prior to reduction. The linear characteristic of the δ⁵³Cr data may reflect the contribution of transport on Cr isotope fractionation.

碩士
國立臺北科技大學
環境規劃與管理研究所
94
There have been studies of electroplating-wastewater treatments with zero valent iron (ZVI) in recent years. Due to the expensive cost of ZVI, scrap iron, a low-cost adsorbent, were used to treat chromate from electroplating wastewater in column reactors. High Cr(VI) removal is expected to achieve and coagulant cost is expected to reduce due to the generation of ferric ion. The influent pH values were controlled at 1.3, 1.5, 1.7 and 2.0. Cr(VI) reduction was reduced as pH increased. When pH≦1.5, the Cr(VI) removal achieved 100%. When Cr(VI) removal was increased, ferrous ion was produced and oxidation-reduction potential (ORP) was getting lower. As the retention time decreased, Cr(VI) removal were less and the operation time increased. For 20 minutes of detention time at pH1.3 or 40 minutes of detention time at pH1.5, 100% Cr(VI) removal were achieved. Effluent pH was 3-4 for the initial stage with high turbidity due to the occurrence of iron coagulation. Hence reduction and coagulation were able to achieved for adding just one chemical (scrap iron) and the cost for the scrap/Cr(VI) was lower than ZVI/Cr(VI) process due to the generation of ferric ion to save extra ferric ion needed.

碩士
國立中興大學
土壤環境科學系所
99
Humic acids (HAs) are one of the major components in soils which influence greatly the behavior and fate of heavy metals in the environment. Due to the high chemical and structural heterogeneities of HAs, of which domains in humic substances involved in Cr (VI) removal are barely understood. Thus, in the study, a repetitive extract and ultrafiltration techniques were used to fractionate HA into several fractions containing various proportions of aliphatic and aromatic carbons and molecular weights. Three fractions (denoted as F1, F2, and F3) and five molecular weights (MWs) of HAs (Bulk, >100kD, 50-100kD, <10kD) were obtained by a repetitive extraction method and by using a hollow-fiber tangential flow filtration (TFF) system, respectively, from a Yangming Mountain peat soil, Taiwan. In the study, the chemical properties of each HA fraction were characterized by FTIR and 13C-NMR spectroscopy before and after reaction with Cr(VI). Spectral analyses found that the contents of aromatic and oxygen-containing C decreased with a progressive extraction, and lower molecular weights of HAs contained more aromatic carbons and carboxyl groups. The interactions of each HA fractions with Cr(VI) showed that Cr (VI) removal could be enhanced under illumination, and the removal was attributed to Cr(VI) reduction. The redox product, i.e, Cr(III), was either adsorbed on residual HAs or released into the solution. A higher aromatic C content and a smaller molecular weight of humic acid exhibited a greater efficiency for Cr(VI) reduction, and the 13C NMR and FTIR results indicated that the carboxyl and phenolic groups enriched in these domains of HAs were responsible for the enhancement of Cr (VI) reduction. Time-dependent FTIR and 13C NMR spectra suggested that the activated sites on HA were rapidly consumed or dissolved into the solutions upon Cr(VI) oxidation. Thus, Cr(VI) may react directly with dissolved organic C (DOC) in the solution instead of on the surfaces of HA fractions. In conclusion, the O-containing groups of HAs were dominant sites for Cr(VI) reduction; however, the redox reactions proceeded very slowly unless the light participated to the reaction. With an increase of DOC concentrations upon Cr(VI) interactions with HAs, this study highlighted the possibilities that DOC derived from HAs may react with Cr(VI) much longer to complement the slow reactions between these two reactants. Thus, HAs may still have a profound effect to Cr(VI) reduction in a soil system.

碩士
國立中興大學
土壤環境科學系所
100
This study mainly investigates the interactions of Cr(VI), a toxic anion in the environment, with goethite with different particle sizes. Several methods were used for goethite syntheses, including ferrihydrite heat transformation, ferric nitrate acidification, and ferric sulfate, which gave particle sizes of 22, 139, and 449 nm, respectively. In addition, a method adopted from Schwertmanm was employed for preparing goethite with greater particle sizes of 849 and 1207 nm. The results of powder X-ray diffraction (XRD) conformed the goethite structures for each synthesized samples. The particle sizes and morphologies of these goethite samples were further verified using a laser scattering particle size distribution analyzer and a transmission electron microscopy (TEM). Surface areas and pHzpc (zero point charge) for each particle were measured using a BET surface area meter and Zeta meter. Cr(VI) adsorption on goethite complied with Elovich kinetic model and Langmuir adsorption isotherm, and the adsorption behaviors was indifferent with the particle sizes of goethite. The maximum adsorption of Cr(VI) on goethite was in the range 0.0707-0.207 mmol/g, depending on the particle size of goethite. A liner relationship existed between the amount of Cr(VI) adsorption and the goethite particle sizes and the smaller goethite particle exhibited higher adsorption ability, corresponding to its higher surface area. A significant declination of Cr(VI) adsorption on goethite was observed at pH 6-8, related probably to the change in Cr(VI) species (i.e., converting from HCrO4- to CrO42- at the specific pH) or/and an increase of surface negative charges and OH ion concentrations. An apparent endothermic reaction was observed while adsorbing Cr(VI) on goethite. Cr(VI) adsorption on smaller particle size of goethite had higher absorption heat which may lead to a decrease of Cr(VI) desorption from the surfaces of small particles. Small particles revealed a higher efficiency for photo-catalytic reduction of Cr(VI) on goethite, attributing to the higher adsorption ability of Cr(VI) and rapid electric transferring on the surfaces of small goethite particles.

abstract: Hexavalant chromium (Cr(VI)) poses an emerging concern in drinking water treatment with stricter regulations on the horizon. Photocatalytic reduction of Cr(VI) was investigated as an engineering scale option to remove hexavalent chromium from drinking or industrial waters via a UV/titanium dioxide (TiO2) process. Using an integrated UV lamp/ceramic membrane system to recirculate TiO2, both hexavalent and total chromium levels were reduced through photocatalytic processes without additional chemicals. Cr(VI) removal increased as a function of higher energy input and TiO2 dosage, achieving above 90% removal for a 1g/L dose of TiO2. Surface analysis of effluent TiO2 confirmed the presence of chromium species.
Dissertation/Thesis
M.S. Engineering 2013

碩士
嘉南藥理科技大學
環境工程與科學系暨研究所
99
Titanium oxides were used for photocatalysis on the treatment of aqueous Cr(VI) in this study by the assistance of sacrificial reagents. Electrons and holes were generated by inducing TiO2 with UV irradiation. The addition of sacrificial reagents could scavenge electric hole (h+) and reduce the recombination of electrons and holes, as well as improve the reduction of Cr(VI) by photogenerated electrons. Five sacrificial reagents, including sodium Acetate, adipic acid, citric acid, 1,2,3,4-Butanetetracarboxylic acid, diethylene-triaminepentaacetic acid, were used to enhance the treatment efficiency of Cr(VI) photoreduction under various light intensity. Results indicate that the optimal condition for remove Cr(VI) with initial 0.04 mmol among 40 minutes was controlled under pH 2 and adding 5 mmol TiO2 and 0.2 mmol DTPA. In addition, the treatment efficiency of Cr(VI) photoreduction was better by controlling the sacrificial reagent to pollutant (Cr(VI)) ratio (SPR) at 5/1 than at other ratios, based on the same Cr(VI) initial concentration. However, even SPR controlled at 5/1, the treatment efficiency of Cr(VI) photoreduction was not good under the initial Cr(VI) controlled at 0.1 mmol. The efficiency of Cr(VI) photoreduction was affected by UV light intensity, photocatalyst dosing, kinds of sacrificial reagents under UV-TiO2 photocatalysis system. The treatment efficiency of Cr(VI) photoreduction increased with pH decreasing and increasing light intensity. Results also reveal that the efficiency of Cr(VI) photoreduction had good and positive correlation with the amount of carboxylic group in sacrificial reagents under the conditions of the same initial Cr(VI) concentration, sacrificial reagents and TiO2 dosages.

碩士
國立中興大學
土壤環境科學系所
97
Humic substances (HS) strongly affect the fate of trace metals in soils and aquatic environments. Because HS is a huge organic molecules with molecular weights ranging from several hundred to several hundred thousands Daltons, the elucidation of which components of HS possess photo-induced properties responsible for photo-reduction of toxic Cr(VI) to Cr(III) is less possible. Therefore, in this study, an ultrafiltration technique was used to fractionate HS, originated from a Taiwan peat soil, into four fractions of different nominal molecular weight (>100 kD, 50~100 kD, 10~50 kD and <10 kD). The specific domains or functional groups of HA involving in Cr(VI) adsorption/reduction were then systemically evaluated. Each fraction of HS was first characterized by elemental analysis and spectroscopic techniques followed by examining the sorption and transformation of Cr(VI) on each fraction of HS under illumination. The results of elemental analysis indicated that the contents of C, H, and N decreased with a decrease in molecular weight of HAs, but the content of O exhibited an opposite tendency. 13C -NMR studies showed that the aromatic C and carboxylic C increased with decreasing the molecular weight of HAs; however, aliphatic C decreased with a smaller molecular weight of HAs. In a dark system, Cr(VI) removal by each fraction of HAs proceeded slowly, particularly at a higher pH. The application of UV light promoted Cr(VI) reduction probably due to the enhancement of electron-transfer between reactants upon the absorption of light energy by specific functional groups on HAs. The rate of Cr(VI) reduction by HAs with a molecular weight of <10kD exhibited the highest which may be attributed to the presence of high contents of aromatic C, carboxylic groups and oxygen containing groups in this fraction of HAs. This conclusion is based on the changes in the structures of HAs before and after reacting with Cr(VI). The results of spectroscopic analysis of HAs found that Cr(VI) treatment would lead to a significant decrease in carboxyl groups, oxygen containing groups and aromatic C in HAs. Because these specific functional groups are concentrated in HAs with a molecular weight of <10kD, the rapid reduction of Cr(VI) by this fraction of HA is expected.

碩士
東海大學
化學系
103
In this thesis, we study the oxidation - reduction reaction mechanisms of Cr(VI)O42-, As(III)O33-, S(IV)O32-and P(III)O33-with Fe(VI)O42-of oxidation - reduction reaction by DFT(Density Functional Theory ) methodB3LYP/6-311++G**in Gaussian 09 for gaseous state and aqueous state by PCM method. Our results have shown that it would be thermodynamically more favorable for the oxidation- reduction reaction in the form of electron transfer when Fe(VI)O42-react with Cr(VI)O42-, As(III)O33-, S(IV)O32-and P(III)O33-in gas state and in aqueous state.

碩士
嘉南藥理科技大學
環境工程與科學系碩士班
96
Zero-valent metal nanoparticles, possessing characterization of fast reaction rate and strong reduction ability have been found to be effective in degrading organic and inorganic aqueous contaminants. However, the aggregation of zero-valent metal nanoparticles can reduce the effective application for in situ decontamination in soil and groundwater. Zero-valent iron nanoparticle composite PVDF microfiltration membranes (ZVI/PVDF) and bimetallic FeNi alloy nanoparticle composite PVDF microfiltration membranes (Fe0Ni0/PVDF) were synthesized with cross linkage of Polyacrylic Acid (PAA) into hydrophobic polyvinylidene fluoride (PVDF) microfiltration membrane which was used as the supported membrane. Supported membrane pore sizes such as 0.1, 0.22, 0.45, and 0.65μm, aqueous pH values, mass loading of zero-valent nanometals and bimetallic mass ratio were evaluated to realize the influences on the reductive removal of chromium(VI) ion from contaminated aqueous solution. Significant reduction efficiency of chromium(VI) ion reached at almost 99.7% when it was contacted with 0.45μm membrane supported of Fe0Ni0/PVDF (Fe:Ni=1:3) in 90 minutes. Fe0Ni0/PVDF composite membrane had higher Cr(Ⅵ) removal efficiency than ZVI/PVDF composite membrane did. Different synthesized methods were used to prepare the Fe0/Ni0/PVDF composite membrane. The extension heating time of PAA solution, the reduction of Fe/Ni bimetallic ratio, and the reduction impregnate time of PVDF into Ni solution could enhance the reductive removal of Cr(Ⅵ).