Temperature-phased anaerobic digestion (TPAD) has become increasingly appealing in recent years due to the pathogen destruction capabilities of the system. However, there has also been concern about the dewatering properties of the sludges created by these systems. A laboratory study was conducted at Virginia Tech to determine the effect of thermophilic solids retention time (SRT) on sludge dewatering properties, to characterize system parameters associated with dewatering, and to understand the mechanisms causing changes in dewatering properties between the thermophilic and mesophilic phases. The study showed that while anaerobic digestion caused dewatering properties to deteriorate, sludges varied little with thermophilic SRT. Acidogenesis was essentially complete after 1.5 days. Subsequent mesophilic digestion resulted in little change to dewatering properties and modest reductions in conditioning doses, but substantial reductions in biopolymer (protein + polysaccharides) occurred. It appears that thermophilic anaerobic digestion creates or releases colloidal materials that cause dewatering to be poor and subsequent mesophilic digestion for 15 days does little to improve sludge properties of TPAD systems. / Master of Science

Waste sludge is frequently treated by anaerobic digestion to kill pathogens, generate methane gas and reduce odors so the sludge can be safely land applied. In an attempt to reduce sludge volumes and improve sludge dewatering properties, the use of thermal hydrolysis (TH), a sludge pretreatment method, has been adopted by numerous wastewater treatment plants, among them being the District of Columbia Water and Sewage Authority (DC WASA). The use of anaerobic digestion in collaboration with thermal hydrolysis has been shown to increase VS removal, COD removal and biogas production. The sludge generated also dewaters to a higher cake solids than from conventional anaerobic digestion. Unfortunately, DC WASA has found that the use of thermal hydrolysis had brought about two major issues. These are: (a) does thermal hydrolysis increase destruction of fats, oils and greases compared to conventional digestion? and (b) is the mixing method used at Virginia Tech (recirculating gas mixing) capable of stripping ammonia from the digester? Therefore the main purpose of this study is to evaluate these issues which occur with the use of the thermal hydrolysis process. Experiments were conducted in two phases. The first phase was to assess the performance of anaerobic digesters via their biogas production with and without long chain fatty acid addition and with or without thermal hydrolysis. This research was further carried out in two stages. First a mixture of unsaturated long chain fatty acids (hydrolyzed and unhydrolyzed) was used. The fatty acid mixture included oleic, linoleic and linolenic acids, which contain one, two and three double bonds, respectively. In the second stage, the effect of a single unsaturated fatty acid (hydrolyzed and unhydrolyzed) was analyzed. If extra gas is generated, grease addition to the digesters will be implemented. If thermal hydrolysis produces more gas, the greases will be added through the thermal hydrolysis unit rather than being added directly to the digester. The results showed that addition of long chain fatty acids greatly increased gas production and the long chain fatty acids that were thermally hydrolyzed generated more gas than the untreated long chain fatty acids, although the gain was not large. The second phase of the study was carried out by alternating the type of recirculating gas mixing (partial and continuous) in the anaerobic bioreactor. To achieve this goal, short-term anaerobic bioreactor studies were conducted by varying the frequency of the gas. The result showed that continuous gas recirculation at the bottom of the digester was responsible for stripping ammonia from the system. It appeared that up to 500 mg/L of ammonia was being stripped from the digester operating at 20 day solids retention time. This suggests that ammonia can be stripped if a reduction of ammonia in the digester was desired. / Master of Science

Washington D.C. Water and Sewage Authority is planning to construct a new anaerobic digestion facility at its Blue Plains WWTP by 2008. The research conducted in this study is to aid the designers of this facility by evaluating alternative digestion technologies. Alternative anaerobic digestion technologies include thermophilic, acid/gas phased, and temperature phased digestion. In order to evaluate the relative merits of each, a year long study evaluated the performance of bench scale digestion systems at varying solids retention times (SRT) and organic loading rates (OLR). The digesters were fed a blend of primary and secondary residuals from the Blue Plains wastewater treatment facility. In each study phase, temperature phased anaerobic digestion was compared to single stage mesophilic digestion (the industry standard) at the same SRT. Single stage thermophilic digestion was evaluated by sampling the first thermophilic stage of the temperature phased digestion systems throughout the study. Additionally, the first phase study compared acid/gas phased digestion to temperature phased and single stage mesophilic digestion. Results of the study demonstrated that the temperature phased digestion system consistently performed better than the other systems during each study phase by having higher volatile solids reduction (VSR), higher methane production, and lower residual biological activity. The highest observed VSR during the study (67%) occurred in a temperature phased digestion system operated at 7.5 days in each stage. Based on these results, it seems a suitable candidate for the Blue Plains digestion facility. Additionally, odor studies performed in conjunction with the research presented in this paper have shown distinct advantages for the temperature phased process. / Master of Science

Ph.D., Faculty of Science, University of the Wiwatersrand, 2011 / Biological production of hydrogen gas has received increasing interest from the international community during the last decade. Most studies on biological fermentative hydrogen production from carbohydrates using mixed cultures have been conducted in conventional continuous stirred tank reactors (CSTR) under mesophilic conditions. Investigations on hydrogen production in reactor systems with attached or self-immobilized microbial growth have also appeared recently in the literature. These investigations on attached or self-immobilised bacteria involve hydrogen production in the mesophilic and thermophilic temperature range. The present study investigated the design and operational features of anaerobic fluidized granular bed bioreactor (AFGB) system which would facilitate the simultaneous achievement of high productivities (HPs) and high hydrogen yields (HYs).Where high HPs is greater than 120 mmol H2 /(L.h) and HYs greater than 4 mol H2/mol glucose. Theoretical maximum yield for an exponentially growing non-granulated bacterial monoculture will always be less than the thermodynamic maximum of 4 mol H2 /mol glucose: C6H12O6 +4H2O → 2CH3COO- + 4H2 + 4H+ + 2HCO3. The design features included reducing the total non-working or dead volume of bioreactor system. The operational improvements included application of thermophilic temperatures and high rates of de-gassed effluent recycling through the fluidized granular bed. An example of an optimal ratio of effluent recycle rate (R) to bioreactor working volume (V) was (3.0 L/min)/(3.2 L/min) = 0.94 minutes. Under conditions where temperatures were maximised and V/R were minimized the HPs increased to 21.58 L H2 /h. Also under these conditions the HYs increased above 3.0 mol H2/mol glucose. Specific hydrogen productivity for the fluidized granular bed increased from 0.25 L H2 / (g BM.h) or 8.83 mmol H2 / (g BM.h) at 45 oC to 0.525 L H2 / (g BM.h) or 18.03 mmol H2 / ( g BM.h) at 70 oC. A 3.64 fold increase in hydrogen yield occurred with an increase in temperature from 45 oC to 70 oC. XX When expressed in terms of glucose, this represents an increase from 1.34 mol H2 /mol glucose to 4.65 mol H2 /mol glucose. Finally, an evaluation of the net energy production by the AFGB system revealed a positive energy balance, making thermophilic biohydrogen production energetically viable from a commercial perspective.

Na presente pesquisa, utilizou-se a técnica molecular de Eletroforese em Gel de Gradiente Desnaturante (DGGE) e microscopia óptica (contraste de fase e fluorescência) para caracterizar a comunidade procarionte estabelecida em quatro biometanizadores de 50 L e em três biometanizadores de 5 L, cujo substrato principal foi a fração orgânica dos resíduos sólidos urbanos (FORSU) acrescida de serragem (12% nos biometanizadores de 50 L e 20% nos de 5 L) e lodo de esgoto (9% e 18% nos biometanizadores de 50 L; 40% e 60% nos de 5L). Pela análise do perfil das bandas de DGGE, verificou-se uma alteração na estrutura da comunidade de bactérias presentes no chorume dos biometanizadores de 50 L entre 60 e 120 dias de operação, período caracterizado pelo acúmulo de ácidos graxos voláteis, consumo crescente de alcalinidade, queda de pH e aumento da demanda química de oxigênio, resultando na baixa remoção de sólidos totais voláteis e na ausência de metano no biogás. Pela análise de microscopia de fluorescência, não foram detectadas metanogênicas em nenhuma das amostras de chorume dos biometanizadores de 50 L, sendo que as principais morfologias e formas de agrupamento visualizadas foram: bacilo, diplobacilos, vibrião, espirilo, diplococos e cocos em cadeia. Os biometanizadores de 5 L, por serem inoculados com maiores proporções de lodo de esgoto do que os biometanizadores de 50 L, apresentaram um processo mais equilibrado. Um dos tratamentos de 5 L (ETE 2) obteve a maior similaridade para o domínio Archaea entre o digestato e o respectivo inóculo, demonstrando a adaptação das arqueas exógenas ao substrato principal (FORSU), sendo esse o único tratamento para o qual detectou-se metano no biogás. Os resultados sugeriram que monitorar a comunidade microbiana que se desenvolve e atua no processo de biometanização pode trazer maior sensibilidade e especificidade na detecção e confirmação de instabilidades do sistema, garantindo intervenções somente quando necessário. / This dissertation addresses the use of the molecular technique of Denaturing Gradient Gel Electrophoresis (DGGE) and light microscopy (phase contrast and fluorescence) for the characterization of the prokaryotic community established in four 50 L reactors and in three 5 L reactors whose main substrate was the organic fraction of municipal solid wastes (OFMSW) plus sawdust (12% in 50 L reactors and 20% in 5 L reactors) and sewage sludge (9% and 18% in 50 L reactors; 40% and 60% in 5 L reactors). The analysis of the profile of DGGE bands revealed a change in the structure of the bacterial community present in the slurry of 50 L reactors between 60 and 120 days of operation, a period characterized by the accumulation of volatile fatty acids, increasing consumption of alkalinity, decrease in pH and increase in the chemical oxygen demand, which resulted in a lower removal of volatile total solids and absence of methane in the biogas. The fluorescence microscopy analysis detected no methanogenics in the slurry samples from 50 L reactors and the main morphologies and grouping forms displayed were bacillus, diplobacilos, vibrio, spirillum, diplococci and coconuts in chain. The 5 L reactors, inoculated with higher proportions of sewage sludge than the 50 L reactors, showed a more balanced process. One of the treatments (ETE 2) displayed the highest similarity for the Archaea domain between the digestato and the respective inoculum, which demonstrates the adaptation of the exogenous archaea to the main substrate (OFMSW). It was the only treatment in which methane was detected in the biogas. The results suggest the monitoring of the microbial community that develops and acts in the biomethanization process can provide higher sensitivity and specificity for the detection and confirmation of instability of the system and ensure interventions only when necessary.

Na presente pesquisa, utilizou-se a técnica molecular de Eletroforese em Gel de Gradiente Desnaturante (DGGE) e microscopia óptica (contraste de fase e fluorescência) para caracterizar a comunidade procarionte estabelecida em quatro biometanizadores de 50 L e em três biometanizadores de 5 L, cujo substrato principal foi a fração orgânica dos resíduos sólidos urbanos (FORSU) acrescida de serragem (12% nos biometanizadores de 50 L e 20% nos de 5 L) e lodo de esgoto (9% e 18% nos biometanizadores de 50 L; 40% e 60% nos de 5L). Pela análise do perfil das bandas de DGGE, verificou-se uma alteração na estrutura da comunidade de bactérias presentes no chorume dos biometanizadores de 50 L entre 60 e 120 dias de operação, período caracterizado pelo acúmulo de ácidos graxos voláteis, consumo crescente de alcalinidade, queda de pH e aumento da demanda química de oxigênio, resultando na baixa remoção de sólidos totais voláteis e na ausência de metano no biogás. Pela análise de microscopia de fluorescência, não foram detectadas metanogênicas em nenhuma das amostras de chorume dos biometanizadores de 50 L, sendo que as principais morfologias e formas de agrupamento visualizadas foram: bacilo, diplobacilos, vibrião, espirilo, diplococos e cocos em cadeia. Os biometanizadores de 5 L, por serem inoculados com maiores proporções de lodo de esgoto do que os biometanizadores de 50 L, apresentaram um processo mais equilibrado. Um dos tratamentos de 5 L (ETE 2) obteve a maior similaridade para o domínio Archaea entre o digestato e o respectivo inóculo, demonstrando a adaptação das arqueas exógenas ao substrato principal (FORSU), sendo esse o único tratamento para o qual detectou-se metano no biogás. Os resultados sugeriram que monitorar a comunidade microbiana que se desenvolve e atua no processo de biometanização pode trazer maior sensibilidade e especificidade na detecção e confirmação de instabilidades do sistema, garantindo intervenções somente quando necessário. / This dissertation addresses the use of the molecular technique of Denaturing Gradient Gel Electrophoresis (DGGE) and light microscopy (phase contrast and fluorescence) for the characterization of the prokaryotic community established in four 50 L reactors and in three 5 L reactors whose main substrate was the organic fraction of municipal solid wastes (OFMSW) plus sawdust (12% in 50 L reactors and 20% in 5 L reactors) and sewage sludge (9% and 18% in 50 L reactors; 40% and 60% in 5 L reactors). The analysis of the profile of DGGE bands revealed a change in the structure of the bacterial community present in the slurry of 50 L reactors between 60 and 120 days of operation, a period characterized by the accumulation of volatile fatty acids, increasing consumption of alkalinity, decrease in pH and increase in the chemical oxygen demand, which resulted in a lower removal of volatile total solids and absence of methane in the biogas. The fluorescence microscopy analysis detected no methanogenics in the slurry samples from 50 L reactors and the main morphologies and grouping forms displayed were bacillus, diplobacilos, vibrio, spirillum, diplococci and coconuts in chain. The 5 L reactors, inoculated with higher proportions of sewage sludge than the 50 L reactors, showed a more balanced process. One of the treatments (ETE 2) displayed the highest similarity for the Archaea domain between the digestato and the respective inoculum, which demonstrates the adaptation of the exogenous archaea to the main substrate (OFMSW). It was the only treatment in which methane was detected in the biogas. The results suggest the monitoring of the microbial community that develops and acts in the biomethanization process can provide higher sensitivity and specificity for the detection and confirmation of instability of the system and ensure interventions only when necessary.

No description available.

Anaerobic digestion of wastewater sludge has widely been in application for stabilization of sludge. With the increase in hauling cost and many environmental and health concerns regarding land application of biosolids, digestion processes generating minimized sludge with better effluent characteristics is becoming important for many public and wastewater utilities. This study was designed to investigate the performance of anaerobic-aerobic-anaerobic digestion of sludge and compare it to anaerobic-aerobic digestion and single stage mesophilic digestion of sludge. Experiments were carried out in three stages: Single-stage mesophilic anaerobic digestion (MAD) 20d SRT; Sequential Anaerobic/Aerobic digestion (Ana/Aer); and Anaerobic/Aerobic/Anaerobic digestion (An/Aer/An). The Anaerobic/Aerobic/Anaerobic digestion of sludge was studied with two options to determine the best option in terms of effluent characteristics. The two sludge withdrawal options were to withdraw effluent from the anaerobic digester (An/Aer/An – A) or withdraw effluent from the aerobic digester (An/Aer/An – B). Different operational parameters, such as COD removal, VS destruction, biogas production, Nitrogen removal, odor removal and dewatering properties of the resulting biosolids were studied and the results were compared among different processes. From the study, it was found that An/Aer/An – B (wastage from aerobic reactor) provided better effluent characteristics than An/Aer/An – A (wastage from anaerobic reactor), Ana/Aer or conventional MAD. The study also shows that the Anaerobic/Aerobic/Anaerobic (An/Aer/An, with wastage from the aerobic or anaerobic digester) digestion of the sludge can improve the biosolids quality by improving the dewatering capabilities, with lower optimum polymer dose, reduced CST and increased cake solid concentration, and reduce the odor generation from the biosolids. Both An/Aer/Ana – A and An/Aer/An – B gave 70% VS removal, compared to 50% with single MAD and 62% with only Ana/Aer. COD removal of both An/Aer/An – A and An/Aer/An – B was 70%, while it was 50% and 66% for single MAD and Ana/Aer respectively. In the aerobic reactors of Ana/Aer and An/Aer/An - B, nitrification and denitrification with removal of nitrogen was observed. The An/Aer/An – B system had more ammonia and TKN removal (70%) than Ana/Aer (64%). The effluent from each stage was analyzed for dewatering ability, cake solid concentration and odor production potential. Compared with a single Ana/Aer system, the extra anaerobic step in An/Aer/An – A and – B reduced polysaccharides in the effluent. The Ana/Aer system released less protein than the conventional MAD system and the addition of the second anaerobic step - especially with system An/Aer/An – B (discharge from aerobic reactor) - greatly reduced protein, resulting in improved dewaterability and less polymer demand. An/Aer/An (both of the options: A and B) had lower CST than single MAD (both 15d and 20d SRT) and Ana/Aer. Compared to Ana/Aer, a reduction of 52% for An/Aer/An – A and 20% for An/Aer/An – B in polymer dose requirement was observed, indicating improved dewatering characteristics. The An/Aer/An – B has higher biosolid cake concentration than MAD or Ana/Aer. The results showed that An/Aer/An (both options: A and B) biosolid had lower odor generation potential than single MAD (15d and 20d SRT) or Ana/Aer. Of all the stages,the An/Aer/An – A and – B system, generated odor which peaked at shorter time and lasted for shorter duration of time. / Master of Science

Doctor of Philosophy / Department of Biological & Agricultural Engineering / James K. Koelliker / This research provides a deterministic model of in-vessel composting, based on Monod’s growth kinetics, to mirror biological-mixture decomposition. Existing models predict temperature curves assuming a single temperature-range organism, using a soluble (simple sugar) substrate, with bacteria as the microorganism, and they ignore the different temperature range environments that impact the growth rates of mesophilic and thermophilic microorganisms. The new computer-simulated model, written in MATLAB® by The MathWorks, has six unique features. First, three major carbon chain substrate groups are utilized: soluble, hemicellulose/cellulose, and lignin. An additional substrate group is used for inert substrates. Second, three major microorganism groups are utilized: bacteria for soluble substrate, actinomycetes for cellulose substrate, and fungi for lignin substrate. Third, two temperature-range microorganisms are included: mesophilic and thermophilic. Fourth, the model accounts for the death of microorganisms as the temperature transitions between the temperature ranges. Most of the dead cellular mass is returned to soluble substrate for reutilization and a portion is considered resistant to biological decomposition and is added into the lignin substrate. Fifth, stoichiometric equations account for substrate and microorganism compositions, oxygen and nitrogen requirements, and carbon dioxide and water production. Sixth, the relationship between biological activity and water is better defined. Experimental research was conducted to validate the model. Laboratory analysis distinguished the substrate types. The results indicate the model did differentiate between different levels of substrate types, and the mesophilic and thermophilic microorganism types. Also, the model did differentiate between the bacteria, actinomycetes and fungi. The influence was small, however, because of the different maximum growth rates of the three types of microorganisms. Returning dead microbes to the substrate pools as a result of temperature transitions affected the model results positively. Additional research is needed to account for the influence of volume reduction, develop a better microbial growth curve, include particle size influence, add temporal temperature fluctuations to the external boundary conditions, incorporate pH and nitrogen availability, and develop a three-dimensional model. KEY WORDS. Aerobic composting, mathematical composting model, substrate types, microorganism types, microorganism temperature range, mesophilic, thermophilic, microbial death utilization, moisture composting relationship.

O presente estudo avaliou o efeito do TDH (tempo de detenção hidráulica) (24 a 1 h) na produção de H2 em reator anaeróbio de leito granular expandido (Expanded Granular Slugde Bed) (ESGB) sob condições mesofílicas (30 ± 2 °C), com cultura mista e a partir do caldo de cana nas concentrações: 5, 10 e 15 g L-1, nos reatores EGSB5, EGSB10 e EGSB15, respectivamente. Foram atingidos valores máximos de produção volumétrica de H2 (PVH) ao decrescer o TDH para: 1 h no EGSB5 (6,96 L d-1 L-1); 1 h no EGSB10 (19,14 L d-1 L-1); e 2 h no EGSB15 (52,40 L d-1 L-1). Os resultados corroboram a afirmação de que reatores de alta taxa como o EGSB suportam aplicação de cargas mais elevadas, visto que o rendimento de H2 (Hydrogen Yield) (HY) máximo (0,73 mol H2 mol-1 hexose) foi observado no EGSB15 para a taxa de carregamento orgânico (TCO) igual a 182,9 kgcarboidrato m-3 d-1. Os HY visualizados no presente estudo foram inferiores aos observados nos estudos em que utilizaram culturas puras, isto pode ocorrer devido ao fato de que o tratamento térmico não é capaz de selecionar apenas culturas produtoras de H2. Foram identificados os possíveis consumos de H2 em consequência à homoacetogênese, com percentuais máximos de ácido acético (HAc) de 59,0 %, 50,0 % e 25,0 % em relação aos demais metabólitos produzidos nos EGSB5, EGSB10 e EGSB15, respectivamente. Devido à provável ocorrência de homoacetogênese o H2 detectado não pode ser inteiramente atribuído a presença de HAc, atribui-se então a produção de H2 à rota de produção de ácido butírico (HBu). Coincidentemente com o HY máximo, as concentrações e percentuais de HBu foram de 1,95 g L-1 e 44,0 % para o EGSB10 no TDH de 4 h, e de 4,07 g L-1 e 43,0 % para o EGSB15 no TDH de 2 h. De modo geral, a redução do TDH de 24 a 1 h melhorou a produtividade de H2. Observou-se devido à elevada PVH, que o caldo de cana pode ser uma alternativa viável para a produção de H2 em larga escala. / The present study evaluated HRT (hydrualic retention time) (24 to 1 h) effect on H2 production in anaerobic expanded granular sludge bed reactor (ESGB) under mesophilic conditions (30 ± 2°C), with mixed culture and sugarcane juice concentration of 5, 10 and 15 g L-1 in EGSB5, EGSB10 and EGSB15, respectively. Maximum hydrogen production rates (HPR) were visualized by decreasing TDH to: 1 h in EGSB5 (6.96 L d-1 L-1); 1 h at EGSB10 (19.14 L d-1 L-1); and 2 h in EGSB15 (52.40 L d-1 L-1). Results attest that high rate reactors such as EGSB support higher loads application, since maximum hydrogen yield (HY) was observed in EGSB15 for the highest organic loading rate (OLR) applied (0.73 mol H2 mol-1 hexose in OLR 182.9 kgcarboidrato m-3 d-1). HY visualized in present study were lower than those observed in studies using pure cultures, this may occur due to heat treatment is not able to select only H2 producing cultures. Possible H2 intakes were observed as a consequence of homoacetogenesis, with maximum acetic acid (HAc) 59.0%, 50.0% and 25.0% for EGSB5, EGSB10 and EGSB15, respectively. Due to probable occurrence of homoacetogenesis the H2 production can\'t be entirely attributed to HAc, then H2 production is attributed to butyric acid (HBu) route. Coincidentally with maximum HY, the HBu concentrations and percentages were 1.95 g L-1 and 44.0% for the EGSB10 in TDH 4 h, 4.07 g L-1 and 43.0% for EGSB15 in TDH 2 h. Overall, the TDH reduction from 24 to 1 h improved H2 productivity. Due to high HPR observed the sugarcane juice can be a feasible alternative for H2 production on large scale.