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Transport of 10–40 μm gellan gum microbeads was studied in horizontal sand columns to evaluate the feasibility of using gel-encapsulated bacteria for bioaugmentation of contaminated aquifers. Three 5.2×110 cm columns were packed with sand (column A: 0.5–2 mm, column B: 0.25–2 mm, and column C: 0.125–2 mm). Microbeads in artificial groundwater were injected at 0.5 l h −1 during intermittent 12-h periods. Breakthrough of microbeads increased with injection time, varying as a descending function of travel distance. After 72 h of injection, about 75% of injected microbeads were dispersed across a 5–110 cm distance from the inlet in column A, compared to 78% across a 5–50 cm in column B, and 76% across a 5–20 cm in column C. The wider dispersion of microbeads across the length of column A, compared to those observed in columns B and C, suggests a higher potential for the formation of a uniform bioactive zone of encapsulated cells across a sandy aquifer with such grain size distribution and hydrodynamic properties.

This study analyzed global trends in the industrial use ofanaerobic wastewater treatment systems. Information on over 750anaerobic systems installed over the last two decades by three leading suppliers of anaerobic systems, namely ADI SystemsInc., Biothane Corporation, and Paques, showed exponential growthin the use of industrial anaerobic wastewater systemsinternationally up to the mid-1990s. After 1994, the number ofannual installations declined, and has been relatively constantover the last three years. The North American market was shown tobe relatively volatile, with no clear indication of futuregrowth, while the European market was found to be relativelymature. In North America, most of the anaerobic wastewatertreatment systems are serving breweries (26%), potato processingindustries (11%), or pulp and paper industries (9%). Ananalysis of the market history of the commercial anaerobic modelssuggests the phasing out of traditional UASB and fermentormodels, and the potential for growth of high-capacity and high-rate systems (>20 kg m-3 d-1) such as the BiothaneEGSB and the Paques Internal Circulation (IC) systems. Future efforts should focus on research into new designs for high-rate and high-capacity systems, and on the encouragement of economic incentivesfor industries implementing anaerobic wastewater treatmentsystems. A market study on other methods of wastewater treatment(e.g. aerobic treatment) is also recommended, to provide insightinto current economic trends in the area of environmental biotechnology.

A special microbial consortium adapted to degrade petroleum hydrocarbons at limited availability of oxygen, transformed benzene, a highly toxic and carcinogenic contaminant of groundwater and soil, at low initial dissolved oxygen (DO) concentrations of 0.05-2 mg/L. The employed initial concentrations of dissolved oxygen were considerably lower than the previously reported values. Under these conditions, the overall transformation of benzene ranged from 34% � 1.7% to 100%, considerably higher than the theoretical predictions for complete mineralization of benzene based on the requirement of 3.08 mg oxygen/mg benzene. Unlike biotransformation that proceeded at the lowest examined DO concentration of 0.05 mg/L, the mineralization of benzene, defined by its conversion to CO2 and water, required a minimum DO concentration of 0.2 mg/L. The mineralization of benzene under microaerophilic conditions (DO < 2 mg/L), ranged from 0.83% � 0.06% to 89% � 1.3%, which was less than the theoretical predictions at any given initial DO concentration. The regulatory effects of dissolved oxygen concentration or its partial pressure on the activities of enzymes catalyzing the biotransformation of aromatic hydrocarbons was postulated to account for the reduced mineralization of benzene. The ratio between the transformed benzene and the consumed oxygen increased with the decrease of initial DO concentration, reaching a value of 2.8, considerably higher than the theoretical value of 0.33 obtained for a complete aerobic oxidation of benzene. Phenol was the major and the most stable intermediate metabolite during the biotransformation of benzene at low concentrations of DO. While benzene transformation stopped after the depletion of oxygen in the experimental system, phenol continued to accumulate under strictly anaerobic conditions, indicating its formation from an alternative carbon source, possibly biomass. � 2002 Government of Canada. Exclusive worldwide publication rights in this article have been transferred to Wiley Periodicals, Inc. Biotechnol Bioeng 79: 347-355, 2002.

In this study, the feasibility of using a mineralization test under coupled aerobic/anaerobic conditions was demonstrated. The coupling of anaerobic methanogenic and aerobic methanotrophic conditions in a microcosm required the presence of both a carbon source for anaerobic metabolism and oxygen for aerobic metabolism. These requirements were fulfilled by using a slow hydrolyzing organic matter along with intermittent addition of oxygen to the bottle headspace. Perchloroethylene (PCE) mineralization tests confirmed the effectiveness of the proposed methodology as well as PCE mineralization under coupled conditions.

Anaerobic degradation of pentachlorophenol (PCP) is an example of a process that may benefit from enrichment or bioaugmentation. In one approach, enrichment acceleration was attempted by applying an on-line control-based selective stress strategy to a native anaerobic upflow sludge bed (UASB) system; this strategy linked PCP loading rate to methane production. As a result, the reactor biomass potential for PCP complete dechlorination reached a rate of 4 mg g⁻¹ volatile suspended solid (VSS) day⁻¹ within a period of 120 days. In another approach, a pure culture, Desulfitobacterium frappieri PCP-1, a strictly anaerobic Gram-positive bacterium, was used to augment the granular biomass of the UASB reactor. This also resulted in a specific degradation rate of 4 mg PCPg⁻¹ VSS day⁻¹; however, this potential was attained within 56 days. Fluorescent in situ hybridization (FISH) showed that the PCP-1 strain was able to rapidly attach to the granule and densely colonize the outer biofilm layer., 9th World Congress on Anaerobic Digestion, September 2-6, 2001, Antwerp, Belgium, Series: Water Science and Technology

Extensive characterization of a nitrate-contaminated site at a Canadian airport revealed that natural attenuation of the plume was limited due to aerobic conditions. However, nitrate removal rates as high as 1.4 mg-N/(L/day) were observed in batch tests carried out under denitrifying conditions with an added carbon source. On the basis of these results, a field denitrification pilot test using a setup of vertical withdrawal and injection wells was carried out. Ethanol was used as a carbon source to stimulate the growth and activity of indigenous denitrifying bacterial populations. Denitrification rates of up to 1.2 mg-N/(L/day) were achieved during the test. The test confirmed the feasibility of the technology, which uses the indigenous bacterial populations for denitrification and transforms the aquifer into a subsurface bioreactor.

The influence of ultraviolet photolysis as a pretreatment to the aerobic and anaerobic biological mineralization of a 14C-polyacrylamide was assessed using a series of radiorespirometry bioassays. The polyacrylamide studied was non-ionic with molecular weights ranging between 100,000 and 1 million. Aerobic and anaerobic biomineralization of the unphotolysed (raw) polyacrylamide was found to be only 0.60% and 0.70%, respectively, after 6 weeks of incubation, and hence indicative of the natural recalcitrance of polyacrylamide to microbial degradation. The effectiveness of UV irradiation in the physical breakdown of the polyacrylamide chain into oligomers was demonstrated by the shift in the molecular weight distribution and the positive correlation between the time of irradiation and the degree of its biological mineralization. The molecular weight fraction below 3 kD, which represents only 2% of the raw polyacrylamide, was increased to 41, 60 and 80% after 12, 24 and 48 hours of photolysis, respectively. This in turn, yielded, after 6 weeks of incubation, an aerobic mineralization of 5, 17 and 29% of 150 mg/L polyacrylamide, respectively, and an anaerobic mineralization of 3, 5 and 17%, respectively. Biomass acclimation substantially improved the specific initial rate of biomineralization of the photolysed polyacrylamides, but not the overall percentage of polyacrylamides mineralized.

The literature is showing an increasing trend in the use of microalgal biomass for the production of biofuel, with a recent keen interest for the conversion of microalgae into methane. The methane potential from Phaeodactylum tricornutum was similar for the whole algae, 362. ±. 5. L/kg total volatile solid (TVS), compared with a sample from which the lipids were extracted, at 358. ±. 6. L/kg TVS. The anaerobic digestion of long chain fatty acids (LCFAs) representative of the dominant acids found in P. tricornutum during 22. weeks of incubation demonstrated that the usual incubation time of typical anaerobic digesters (3-6. weeks) is insufficient to hydrolyze the lipids and maximize the energy yield contained in the microalgae. The results from methane potential assays targeting the LCFAs that were found in significant concentrations in P. tricornutum, namely palmitic, palmitoleic and eicosapentaenoic (EPA) acids), at concentration of 2.5 and 1.25. g/L, showed a slow but high yield with palmitic acid (802. ±. 16. L/kg), inhibition from palmitoleic acid and fair degradation of EPA (442. ±. 67. L/kg). There was a 27% increase in the methane yield from a reconstituted P. tricornutum containing 25% of LCFA compared to 10%, at 456. ±. 1 vs 363. ±. 5. mL. STP/g TVS. Increasing the free fatty acid fraction to 50% in the microalgal biomass resulted in the inhibition of the digestion after production of methane during the first 11. days of incubation.

Electricity generation in a microbial fuel cell (MFC) fed with carbon monoxide (CO) has been recently demonstrated; however, the microbial ecology of this system has not yet been described. In this work the diversity of the microbial community present at the anode of CO-fed MFCs was studied by performing denaturing gradient gel electrophoresis (DGGE) and high-throughput sequencing (HTS) analyses. HTS indicated a significant increase of the archaeal genus Methanobacterium and of the bacterial order Clostridiales, notably including Clostridium species, while in both MFCs DGGE identified members of the bacterial genera Geobacter, Desulfovibrio, and Clostridium, and of the archaeal genera Methanobacterium, Methanofollis, and Methanosaeta. In particular, the presence of Geobacter sulfurreducens was identified. Tolerance of G. sulfurreducens to CO was confirmed by growing G. sulfurreducens with acetate under a 100 % CO atmosphere. This observation, along with the identification of acetogens, supports the hypothesis of the two-step process in which CO is converted to acetate by the carboxidotrophic Bacteria and acetate is then oxidized by CO-tolerant electricigenic Bacteria to produce electricity. © 2013 Her Majesty the Queen in Right of Canada.

Two previously unknown modes of biomineralization observed in the presence of Carboxydothermus hydrogenoformans are presented. Following the addition of NaHCO3 and the formation of an amorphous calcium phosphate precipitate in a DSMZ medium inoculated with C. hydrogenoformans , two distinct crystalline solids were recovered after 15 and 30 days of incubation. The first of these solids occurred as micrometric clusters of blocky, angular crystals, which were associated with bacterial biofilm. The second solid occurred as 30-50 nm nanorods that were found scattered among the organic products of bacterial lysis. The biphasic mixture of solids was clearly dominated by the first phase. The X-ray diffractometry (XRD) peaks and Fourier transform infrared spectroscopy (FTIR) spectrum of this biphasic material consistently showed features characteristic of Mg-whitlockite. No organic content or protein could be identified by dissolving the solids. In both cases, the mode of biomineralization appears to be biologically induced rather than biologically controlled. Since Mg is known to be a strong inhibitor of the nucleation and growth of CaP, C. hydrogenoformans may act by providing sites that chelate Mg or form complexes with it, thus decreasing its activity as nucleation and crystal growth inhibitor. The synthesis of whitlockite and nano-HAP-like material by C. hydrogenoformans demonstrates the versatility of this organism also known for its ability to perform the water-gas shift reaction, and may have applications in bacterially mediated synthesis of CaP materials, as an environmentally friendly alternative process. © 2014 Haddad et al.

The conversion of carbon monoxide (CO) into hydrogen (H2) by a Carboxydothermus hydrogenoformans pure culture was investigated and optimized in a 35 L gas-lift reactor. The reactor was operated with a continuous supply of gas for 3 months. Reactor performance was evaluated under various operational conditions, such as gas recirculation rates (0.3 and 1.5 L min−1), CO feeding rates (from 0.05 to 0.46 mol L−1reactor day−1) and bacto-peptone addition to the medium. Overall, the H2 yields were constant at 95 ± 1% and 82 ± 1% ( mol H 2 ⋅ mol CO − 1 ) with growth supported by peptone and unsupported respectively, regardless of the operational conditions tested. At the highest biomass density, a maximum CO conversion activity of 0.17 molCO L−1reactor day−1 or 3.79 LCO L−1reactor day−1 was achieved. The ratio of gas recirculation over CO feed flow rates (QR:Qin) was the major parameter that impacted both biological activity and volumetric gas–liquid mass transfer. The CO conversion performance of the gas-lift reactor was kinetically limited over a QR:Qin ratio of 40, and mass transfer limited below that ratio, resulting in a maximum conversion efficiency of 90.4 ± 0.3% and a biological activity of 2.7 ± 0.4 molCO g−1VSS day−1. Overall, the CO conversion performance in the gas-lift reactor was limited by a low cell density, typical of C. hydrogenoformans planktonic growth. This limitation was found to be the most restrictive factor for higher CO loading rates.

The intermediate metabolites of benzene transformation by a microaerophilic bacterial consortium, adapted to degrade gasoline and benzene at low concentrations of dissolved oxygen (

The effects of aging trichloroethylene (TCE) with a surrogate soil organic matter (SSOM) on its anaerobic biodegradation and desorption characteristics were studied. Surrogate soil organic matter comprised of composted sphagnum moss was used as a model sorbent, and Desulfomonile tiedjei was used as a model member of an anaerobic consortium capable of reductive dechlorination. After TCE was aged with the sterile SSOM for periods of 2, 14, and 30 d, the completely mixed batch reactors were inoculated with D. tiedjei cells and incubated for 5 d. The mass of TCE dechlorinated to cis-1,2-dichloroethylene (DCE) by D. tiedjei in this period decreased by 72% from 2 to 30 d of aging. Although there was an increase in the equilibrium desorption coefficient (Kd) with aging, sorption was completely reversible. Hence, the reduced availability of TCE for degradation was not coupled with irreversible sorption. To examine the longer-term fate of TCE, the unaged TCE-SSOM slurries were inoculated with D. tiedjei and then incubated for longer times (15, 24, and 29 d vs. 5 d). The conversion of TCE to cis-1,2-DCE was up to eight times greater than what was observed in control experiments without SSOM. Therefore, although aging resulted in reduced TCE biodegradation for short-term incubation (5 d), longer-term incubation (29 d) with the unaged SSOM resulted in extensive TCE dechlorination (up to 40%) to cis-1,2-DCE.

The impact of influent dissolved O(2) on the characteristics of anaerobic granular sludge was investigated at various dissolved O(2) concentrations (0.5-8.1 ppm) in 1- and 5-L laboratory-scale upflow anaerobic sludge bed (UASB)-like anaerobic/aerobic coupled reactors with a synthetic wastewater (carbon sources containing 75% sucrose and 25% acetate). The rate of dissolved O(2) supplied to the coupled reactor was as high as 0.40 g O(2)/L(rx).d, and the anaerobic/aerobic coupled reactors maintained excellent methanogenic performances at a COD loading rate of 3 g COD/L(rx).d even after the reactors had been operated with dissolved O(2) for 3 months. The activities of granular sludge on various substrates (glucose, propionate, and hydrogen) were not impaired, and acetate activity was even improved over a short term. However, after 3 months of operation, slight declines on the acetoclastic activities of granules were observed in the coupled reactor receiving the recirculated fluid containing 8.1 ppm dissolved O(2).Methane yield in the anaerobic control reactor and anaerobic/aerobic coupled reactors revealed that a significant aerobic elimination (up to 30%) of substrate occurred in the coupled reactors, as expected. The presence of dissolved O(2) in the recirculated fluid resulted in the development of fluffy biolayers on the granule surface, which imposed a negative impact on the settleability of granular sludge and caused a slightly higher sludge washout. This research shows that the anaerobic/aerobic coupled reactor can be successfully operated under O(2)-limited conditions and is an ideal engineered ecosystem integrating oxic and anaerobic niches. (c) 1996 John Wiley & Sons, Inc.

To monitor the biodegradation of explosives in microcosm experiments, carbon-14 labelled substrates such as 14C-HMX were needed. Many synthetic routes were evaluated to identify the best synthesis of 14C-HMX with high yield and minimal radioactive waste. To synthesize 14C-HMX, acetylation of labelled hexamethylenetetramine (14C-HMTA) was done yielding 3,7-diacetyl-1,3,5,7-tetraazabicyclo-[3.3.1]-nonane (14C-DAPT) which was nitrated to obtain 1,5-diacetyloctahydro-3,7-dinitro-1,3,5,7-tetrazocine (14C-DADN) in one step. Nitrolysis of 14C-DADN was achieved using a mixture of 100% nitric acid and phosphorus pentoxide to yield 14C-HMX. The synthesis of this carbon-14 labelled HMX was optimized first using cold starting materials and then conducted with labelled compounds. This synthesis represents the best way of preparing high purity 14C-HMX with a high yield. Copyright © 1999 John Wiley & Sons, Ltd.

The effects of several pretreatment techniques, including dilution, fungal pretreatment and addition of hydrogen peroxide on the enhancement of anaerobic biodegradability of spent liquor (SL) of the oxygen delignification process of recycled fibers, were evaluated. A 14% COD removal efficiency and a 37% acidification were obtained by the untreated effluent, indicating its low degree of biodegradability. After pretreatment, the efficiency of COD removal and the overall yield of methane production were increased by 24% to 246% and by 26% to 396%, respectively, compared to the untreated liquor. The acidification of spent liquor also increased to more than 70% following the pretreatment. Kinetics analysis of methane production and COD removal implied the production of inhibitory metabolites during the anaerobic biodegradation. The optimal dilution factor for the spent liquor sample under study, to reduce toxi-city while maximizing the specific rates of COD removal and methane production, was predicted to be less than five times.

By supplying a small amount of oxygen to a UASB (upflow anaerobic sludge bed) reactor and thereby supporting aerobic metabolism in an otherwise anaerobic environment, a coupled reactor system was evaluated at a laboratory scale. In order to determine the optimal delivery of oxygen to the coupled reactor systems, two principal operating variables were investigated: the oxygenation rate and the liquid recycle rate. Two UASB and four coupled reactor systems, each 1 litre and operated continuously at a one day hydraulic residence time (HRT) at 35°C, were employed in order to meet these objectives. The oxygenation rate increased the dissolved oxygen concentration to a maximum of 2.9 mg/L and the redox potential up to −9 mV (Eh). Methane was formed even under these conditions, indicating that the aerobic and facultative microorganisms limited the O2 penetration and maintained a reduced microenvironment which was necessary for the methanogens to function. Oxygenation substantially decreased the methane yield and the ratio of methane:carbon dioxide in the biogas. Oxygenation also led to a decrease in the mean particle size of the biomass and lower volatile suspended solid (VSS) levels retained in the reactors. Liquid recirculation aided in maintaining a low redox potential. In spite of the effects of the increased upflow velocity removing the smaller diameter biomass particles from the reactors, more biomass was retained in the reactors at these higher liquid flow rates. No significant impact of oxygenation could be observed on the specific anaerobic activities of the granules, up to the oxygenation mid-range. High oxygenation levels, obtained by combining both high aeration (highest flow of pure O2) and higher liquid recycling rates are necessary to substantially impair the methanogenic activity.

Continuous bioremediation of gasoline-contaminatedwater in a packed-bed biobarrier system underoxygen-limited conditions is discussed. This studywas part of an extensive effort to develop analternative technology for the in situbioremediation of hydrocarbons where there is alimited supply of oxygen. Protruded stainless steelpieces and granulated peat moss were used as packingmaterial to support microbial growth in twobiobarriers. The inoculum was an enrichment culture ofan indigenous microbial population from a soil sample.The biobarriers' inlet gasoline concentrations and thelinear liquid velocities were similar to thosecommonly found at in situ conditions. Gasolineremoval efficiencies ranged from 94% to 99.9% in thestainless steel-packed biobarrier, and from 86.6% to99.6% in the peat moss-packed biobarrier. Effluentgasoline concentrations below 0.03 mg/l were obtainedat gasoline loading rates less than 27.5 mg/l.d in thestainless steel-packed biobarrier. The remainingfraction of gasoline in the effluent consisted mainlyof three aliphatic compounds and not the aromaticcompounds. Both biobarrier packings supported nearcomplete removal of the most soluble aromatichydrocarbons of gasoline (BTEX) under all theconditions examined. The consumption of sulfate andthe presence of sulfate-reducing microorganismssuggested the presence of anaerobic metabolism duringthe degradation of gasoline. Up to 92% gasoline wasremoved during the first 3 cm of the biobarriers'length.

Systems of co-immobilized microorganisms are highly effective for conducting two or more consecutive bioprocesses within close proximity of the source and the sink of substrates. In this work, a general model of a co-immobilized aerobic/anaerobic bacterial system was developed and analyzed. The model was used to optimize pellet design and to study the effect of slow cell growth on process efficiency. The analysis demonstrated that co-immobilization of bacterial species accelerates the rate of biotransformation and provides complete transformation of toxic intermediates.

The present study compares the coupled anaerobic/aerobic integrated system (CANOXIS) operated at different aeration and liquid recycle rates to the conventional upflow anaerobic sludge bed (UASB) system for the laboratory scale treatment of a resin acid-containing effluent. Dehydroabietic and abietic acids were added in equal proportions to a sucrose-based feed stock. Even under oxygenation conditions, methane was formed, indicating that the aerobic and facultative microorganisms consumed oxygen fast enough to maintain a reduced microenvironment essential to the methanogens. Eight weeks of resin acid loading at 100 mg/L exerted no significant effects on the high efficiency and stable performance of UASB reactors. The CANOXIS systems showed with time a reduced discharge of residual resin acids in the effluent and a decrease of the amount of resin acids adsorbed onto the biomass when compared to the UASB reactor.

Aerobic biodegradation of gasoline and its constituents, benzene, toluene and ethylbenzene were studied by an enrichment from soil indigenous microbial population. The enrichment culture completely degraded 16.1-660 mg/l gasoline in 2.5-16 days respectively, without accumulation of any by-products. The kinetics of gasoline as well as benzene, toluene and ethylbenzene biodegradation was investigated with initial gasoline concentrations of 16.1-62.6 mg/l. The maximum specific rates of biodegradation of benzene, toluene and ethylbenzene were 0.12, 0.38 and 0.19 mg mg biomass-1 day-1 respectively. When benzene and toluene were used as sole substrate, the maximum specific rates of their biodegradation were 62.9 and 16.4 times greater than the corresponding values for a mixture (gasoline). The microbial culture was able to mineralize up to 200 mg/l pure toluene and benzene. Maximum mineralization efficiencies of benzene and toluene were 76.7 +/- 5.1% and 76.8 +/- 1.3% respectively. Self-inhibition and competitive inhibition patterns were observed during the biodegradation of benzene and toluene alone and in the mixture respectively. The observed kinetics was modeled according to Andrews' inhibition model.

A commensal system of the aerobic methanotroph Methylosinus sporium with anaerobic methanogens was obtained using cell coimmobilization in a chitosan-lignosulfonate matrix and applied for the dechlorination of tetrachloroethylene (PCE) under coupled anaerobic/aerobic conditions. Due to the oxygen gradient in a bead of immobilized cells, anaerobic transformation of PCE into lower chlorinated compounds was coupled with aerobic dechlorination of these intermediates. At a PCE loading rate of 42.9 mg PCE L r −1day−1 and an oxygenation rate of 4.9 l O2/L r −1day−1, the mineralization efficiency of the commensal system was 88% as opposed to 38% in the control system which was not inoculated with the methanotrophs. The dechlorination rates were 6.7 and 3.0 mg PCE g−1 VSS day−1 for the commensal and control systems, respectively.

The objective of this paper is to present a procedure for the preparation and sterilization of a surrogate soil organic matter (SSOM) to study the chemical and biological interactions that may occur with trichloroethylene (TCE). For this purpose, the SSOM was prepared by composting sphagnum moss, a readily available and rather homogenous material. Both gamma irradiation and autoclaving were compared for their ability to effectively sterilize the SSOM. The efficiency of gamma irradiation, at varying intensities, was compared with that of autoclaving. Irradiation of SSOM at 50 kGy was found to be the most effective method of sterilization tested. Therefore, the effect of 50 kGy gamma irradiation on the surface properties of the SSOM (as evidenced by the cation exchange capacity (CEC), specific surface area (SSA), pH, infrared spectrophotometry (IRS), and TCE sorption isotherms) were compared with the non‐sterilized SSOM. Although there were differences in the CEC and SSA for the two materials, the ...

A model that portrays substrate profiles in a steady-state multispecies granular biofilm is developed and coupled with a biofilm detachment model. The model accounts for glucose, propionate, hydrogen, and acetate transformations performed by three bacterial trophic groups: acidogens, syntrophic bacterial consortia, and methanogens. This model adequately describes the phenomenon of propionate degradation under thermodynamically unfavorable bulk hydrogen concentrations. Also suggested is the superiority of the layered biofilm structure over homogeneous distribution of the trophic groups for anaerobic degradation of organic compounds. Furthermore, model analysis suggests that with increasing bulk glucose concentration biofilm thickness reaches a maximum that is then followed by biofilm disintegration. These results may have an important impact on the design and control of upflow anaerobic sludge bed reactors.

The inhibition of microorganisms in an upflow anaerobic sludge bed and filter reactor was evidenced by a sudden decrease in methane production, a decrease in the chemical oxygen demand elimination, and an increase in the acetate concentration of the treated effluent. The inhibition occurred after a cumulative loading of 3486 mg of resin acids (66% dehydroabietic acid and 34% abietic acid) on 10 g volatile suspended solids of an anaerobic granular sludge. The acetoclastic methanogens were the most inhibited group of bacteria following the reactor failure, while the activity of the hydrogenotrophic methanogens was not affected. During the phase of 9.5 mg/L/d of resin acid feeding, no resin acids were detected in the effluent; sorption of resin acids on the sludge amounted to 6.6 mg/g volatile suspended solids. During the feeding phase of 59 mg resin acids/L/d, the effluent showed an average resin acid concentration of 19 mg/L; the toxicity was half that of the influent (Microtox toxicity tests).

The influence of four different granulation precursors, syntroph-enriched methanogenic consortia, Methanosaeta-enriched, Methanosarcina-enriched nuclei and acidogenic flocs, on the time course of complex granule development and the lag time for start-up was investigated in four upflow anaerobic sludge-bed and filter reactors. Although the operational conditions allowed the maintenance of the same specific growth rate of biomass in the four reactors, granulation proceeded rapidly with syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei. However, granulation was significantly retarded when acidogenic flocs were used as precursors. The granule mean Sauter diameter increased rapidly in the reactor inoculated with syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei and reached, at the end of the experiment, 3.1, 2.7 and 2.4 mm compared to 1.1 mm in that inoculated with acidogenic flocs. This corresponded to a rate of granule size increase of 31, 21, 18 μm/day in syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei, respectively, compared to 7 μm/day in acidogenic flocs. Biomass specific activities (i.e. acidogenic, syntrophic and methanogenic activities) increased stepwise in all reactors with time, especially in those inoculated with syntroph/methanogenic consortia and Methanosaeta nuclei. From these results it appears that syntrophs and Methanosaeta spp. play an important role in the anaerobic granulation process.

A multidisciplinary approach involving chemistry, microbiology, ecotoxicology and environmental engineering was undertaken by the Defence Research Establishment of the Department of National Defence (DREV/DND) and the Biotechnology Research Institute of the National Research Council of Canada (BRI/NRC) to characterize and to optimize the biodegradation potential of TNT and RDX in pure form and in soil. The nature and level of contamination by RDX and TNT in various soils were determined in an interlaboratory study involving both organizations using EPA Method # 8330. Microorganisms were isolated from the native soils and found to be capable of mineralizing (¹⁴CO₂ liberation) RDX under aerobic conditions when the latter was used as sole nitrogen source. RDX disappearance was accompanied by the elimination of toxicity associated with RDX, as determined by the Microtox test. Studies are underway to use the isolated indigenous strain as a bioaugmentation agent for future site application. Thus far TNT showed more toxic effects than RDX and metabolic analysis showed that TNT was biotransformed into the more toxic amine metabolites. In soil these amine metabolites react with humic acids to give recalcitrant and intractable products. To eliminate problems associated with TNT mineralization in soil we thus undertook a study to first wash TNT out of the soil using several water additives and then treat the TNT washings. Preliminary data showed that mineralization of TNT using sewage sludge under both aerobic and anaerobic conditions was enhanced in the presence of cyclodextrins. Further enhancement in the mineralization rate of TNT was obtained after subjecting the soil extract to photolysis. In an integral study, soil heavily contaminated with RDX (2000 ppm) and TNT (1000 ppm) was treated in bioslurry reactors supplemented with sewage sludge under both aerobic and anaerobic conditions. The biological performance of these reactors was monitored using microcosms spiked with ¹⁴C-labelled TNT or RDX. Preliminary data showed that RDX was almost completely mineralized. TNT rapidly disappeared (biotransformation to amino derivatives) with little mineralization. The data obtained from the present aerobic, soil washing and bioslurry reactors studies will be used for the development of practical soil remediation technologies., Fourth International Symposium on Special Topics in Chemical Propulsion : Challenges in Propellants and Combustion 100 Years After Nobel (4-ISICP), May 27-31, 1996, Stockholm, Sweden

Carboxydothermus hydrogenoformans is a thermophilic anaerobic strain most widely known for its ability to produce hydrogen (H2) when grown on carbon monoxide (CO). Although relatively well studied, growth characterization on pyruvate has never been assessed. The present work fully characterizes growth of the bacterium on pyruvate as a sole carbon source. C. hydrogenoformans demonstrated a growth rate of 0.03 h-1, with pyruvate consumption ranging between 0.21 and 0.48 mol · g-1 volatile suspended solid · d-1. A lag phase was also observed when switching from pyruvate to CO. When grown simultaneously on pyruvate and CO, pyruvate consumption was initiated upon CO depletion. This was attributed to pyruvate oxidation inhibition by CO, and not to a diauxic phenomenom. The strain also showed homoacetogenic activity.

This study demonstrates microbial electrolysis cell (MEC) scale-up from a 50. mL to a 10. L cell. Initially, a 50. mL membraneless MEC with a gas diffusion cathode was operated on synthetic wastewater at different organic loads. It was concluded that process scale-up might be best accomplished using a " reactor-in-series" concept. Consequently, 855. mL and 10. L MECs were built and operated. By optimizing the hydraulic retention time (HRT) of the 855. mL MEC and individually controlling the applied voltages of three anodic compartments with a real-time optimization algorithm, a COD removal of 5.7. g LR-1d-1 and a hydrogen production of 1.0-2.6. L LR-1d-1 was achieved. Furthermore, a two MECs in series 10. L setup was constructed and operated on municipal wastewater. This test showed a COD removal rate of 0.5. g LR-1d-1, a removal efficiency of 60-76%, and an energy consumption of 0.9. Wh. per. g of COD removed. © 2012.

The co-culture between Methylosinus sporium, a strictly aerobic methanotroph, and strictly anaerobic methanogens was studied in 5 L aerobic/anaerobic coupled granular sludge reactors under O2-limited conditions. The methanogenic bacteria maintained very good metabolic activities and were able to produce sufficient methane which serviced as substrate for methanotrophic growth. Although other strictly aerobic population proliferated by two orders of magnitude after the granular sludge had been operated under O2-limited conditions for one month, only a limited amount of the added methanotroph remained in the sludge. This result may indicate that M. sporium lacks sufficient O2 affinity to compete with facultative bacteria for the dissolved O2 for their growth.

Efficient anaerobic degradation may be completed only under low levels of dissolved hydrogen in the liquid surrounding the microorganisms. This restraint can be intensified by the limitations of liquid-to-gas H2 mass transfer, which results in H2 accumulation in the bulk liquid of the reactor. Dissolved hydrogen proved to be an interesting parameter for reactor monitoring by showing a good correlation with short-chain volatile fatty acid concentration, namely propionate, which was not the case for the H2 partial pressure. Biogas recycle was performed in a upflow anaerobic sludge bed and filter reactor. The effects of varying the ratio of recycled-to-produced gas from 2:1 (9 l/l reactor per day) to 8:1 (85 l/l reactor per day) were studied. By increasing the liquid—gas interface with biogas recycling, the dissolved hydrogen concentration could be lowered from 1.1 to 0.4 μ m . Accordingly, the H2 sursaturation factor was also reduced, leading to an important improvement of the H2 mass transfer rate, which reached 20.86 h−1 (±9.79) at a 8:1 gas recycling ratio, compared to 0.72 h−1 (±0.24) for the control experiment. Gas recycling also lowered the propionate concentration from 655 to 288 mg l−1 and improved the soluble chemical oxygen demand removal by 10–15%. The main problem encountered was the shorter solid retention time, which could lead to undesirable biomass washout at high gas recycling ratio. This could be circumvented by improving the reactor design to reduce the turbulence within the biomass bed.

Anaerobic granule nuclei enriched in either acidogens, syntrophic consortia, Methanosaeta spp. or Methanosarcina spp. were developed in four upflow bed filter reactors fed with sucrose, an ethanol/acetate mixture, acetate and methanol, respectively. The enrichment process was evaluated by scanning electron microscopy and by the change in trophic specific activities. The four developed granule nuclei presented different settling velocities: 3.2, 8.7, 10.5 and 11.3 m h−1 for the acidogenic floes, the Methanosarcina-, the syntrophic consortia and the Methanosaeta-enriched nuclei, respectively. These velocities were related to the size and the ash content of the various aggregates. Acidogenic floes were relatively small in size (

A 450-m(3) multiplate anaerobic reactor (MPAR) has been started-up in April 1992 for treating wastewater (whey permeate and domestic wastewater) at the Nutrinor (Lactel) cheese factory in Chambord (Québec, Canada). The MPAR consists of four superimposed sections. The liquid flows upwards from one section to the next, while the gas is collected below each plate and evacuated through side-outlets. The wastewater is concurrently distributed at the bottom of the first, second, and third sections, as 50%, 33%, and 17% of the total influent stream, respectively. Granular anaerobic sludge at an initial concentration of 30 kg of volatile suspended solids (VSS) per cubic meter of reactor liquid volume was used to inoculate the reactor. Under normal operation of the factory, the chemical oxygen demand (COD) concentration of the influent ranged from 20 to 37 kg COD m(-3). The reactor organic loading rate (OLR) fluctuated between 9 and 14.7 kg COD m(-3) d(-1) for hydraulic retention times (HRT) maintained between 55 and 68 h. At the highest OLR, the MPAR showed an efficiency of 98% and 92% for soluble and total COD removal, respectively, and a methane production rate averaging around 4 m(3) m(-3) d(-1).Biomass-specific activities ranged between 7 and 51, 1.3 and 8.5, 5.3 and 12.2, 60 and 119, and 119 and 211 mmol g(-1) VSS d(-1) for glucose, propionate, acetate, formate, and hydrogen, respectively. Average equivalent-diameter of the granules was around 0.65 mm. The MPAR reactor generally showed a large capacity for solid retention with a biomass content between 32 and 37 kg VSS m(-3).

A 19.2 l multiplate anaerobic reactor (MPAR) was used to assess the impact of lime (Ca(OH)2) on the anaerobic treatment of whey permeate effluents. The amount of Ca(OH)2 required to maintain the pH of the whey permeate around 5 ranged between 3.0 and 4.5 kg/m3, which corresponded to concentration varying between 1.62 and 2.43 kg/m3. Soluble chemical oxygen demand (COD) removal efficiency exceeded 92% with a methane production rate of 6.7 m3/m3.d. at an organic loading rate (OLR) as high as 20 kg COD/m3.d. Extended operation of the MPAR resulted in the accumulation of significant amounts of calcium precipitates in the sludge bed which reached after three months of operation 0.19, 0.25 and 0.33 kg Ca2+ per kg of suspended solid (SS) in the lower, the middle and the upper compartment of the MPAR, respectively. The volatile suspended solids to suspended solids ratio (VSS/SS) decreased from 0.83 in inoculum to 0.37, 0.22 and 0.08 in the lower, the middle and the upper compartment of the MPAR, respectively. As a result, the soluble COD reduction and the methane production rate decreased to 31% and to 2.3 m3/m3.d. respectively, at OLR of 20 kg COD/m3.d.

Municipal wastewater is a major source of nutrients and pollutants to freshwater and marine ecosystems and current treatment technologies are either expensive or only partially effective at removing them. We cultivated the alga Scenedesmus sp. AMDD at different pH in chemostats and batch photobioreactors in wastewater obtained from a local treatment plant. In batch mode, biomass productivities averaged 130 mg dry weight L − 1 d − 1 , with no significant effect of growth pH detected. Maximum nitrogen and phosphorus removal rates were equivalent to 7% and 0.7% of the biomass productivity rates. Average hydraulic retention times for 90% N and P removal ranged from 6.55 to 6.65 days and 6.50–6.56 days, respectively. Recovered biomass yields ranged from 0.23 to 0.65 kg m − 3 wastewater, equivalent to approximately 5–15 MJ bioenergy m − 3 wastewater based on an average calorific value of 23 MJ kg − 1 d.w. algal biomass. Approximately 65% of energy equivalent could potentially be recovered from the biomass through anaerobic digestion to methane. Cellular N and P content varied, with cells held longer in stationary phase showing higher C:N and C:P ratios indicative of N- and P-limitation, respectively. Analysis of trace metals in the algal biomass indicated near total depletion of Fe, Zn and Cd from the wastewater, and lower, but substantial, uptake and/or adsorption of seven other elements. Cultivation in 2 L continuous chemostats containing wastewater was also conducted. Biomass productivities in chemostats were almost 2-fold greater than the maximum rates in batch cultures. Dissolved N and P in chemostats were both either undetectable or > 99% reduced compared to the wastewater. Production of bioenergy from the chemostats was estimated to be roughly 5.3–6.1 MJ m − 3 d − 1 , significantly higher than in batch culture.

Wastewater treatment processes based on the upflow anaerobic sludge bed design are strongly dependent on the aggregation of biomass into macroscopic granules (1–3 mm) which settle well. The reactor hydrodynamics is of importance in the granulation process. The effect of the liquid upflow velocity υ UP associated with the operating time on the mean granule size and on the hydrogen, formate, acetate, propionate and glucose specific activities was studied, at various specific loading rates, in upflow sludge bed and filter reactors of 13 l fed with sugar wastewater. Reactors which were operated at 0.9 m h −1 behaved as fixed beds while those run at 2.2, 4.4 and 6.6 m h −1 were fluidized, because an immediate spatial gradient of the sludge particle sizes was induced. The υ UP had a significant positive effect on mean granule size. A specific loading rate increase from 0.5 to 1.5 g chemical oxygen demand per gram of volatile suspended solids per day raised proportionally the biomass growth rate, but had no positive effect on the granule development in size. Moreover, the υ UP had little effect on the specific wash-out rate of the smaller particles. Henceforth the resulting final size of granules is essentially a function of the hydrodynamic regime. Major impact on granule net steady size is attributed to several mechanisms related to fluidization: improved penetration of substrates into biofilm; insignificance of liquid shear relative to the shear of gas; reduction of particle friction and attrition with the bed voidage. Acidogenic (glucotrophic) activity decreased with υ UP increased yielding minimum values at intermediate υ UP , between 2 and 5 m h −1 . Postacidogenic activities (propionate, acetate, formate, H 2 ) were positively influenced by υ UP to a slight extent. Glucose activity gradient within the granule bed was highly and inversely correlated to the granule size, while for acetate activity gradients, the correlation was direct, although less strong. These observations are discussed in detail with regard to an ordered distribution of the consortium populations within the granule spatial structure.

The methane produced from the anaerobic digestion of organic wastes and energy crops represents an elegant and economical mean of generating renewable biofuel. Anaerobic digestion is a mature technology and is already used for the conversion of the organic fraction of municipal solid wastes and primary and secondary sludge from wastewater treatment plant. High methane yield up to 0.45 Nm3 CH4/kg volatile solids (VS) or 12,390 Nm3 CH4/ha can be achieved with sugar and starch crops, although these cultures are competing for high quality land with food and feed crops. The cultivation of lignocellulosic crops on marginal and set-aside lands is a more environmentally sound and sustainable option for renewable energy production. The methane yield obtained from these crops is lower, 0.17-0.39 Nm3 CH4/kg VS or 5,400 Nm3 CH4/ha, as its conversion into methane is facing the same initial barrier as for the production of ethanol, e.g., hydrolysis of the crops. Intensive research and development on efficient pretreatments is ongoing to optimize the net energy production, which is potentially greater than for liquid biofuels, since the whole substrate excepted lignin is convertible into methane. Algal biomass is another alternative to food and feed crops. Their relatively high methane potential (up to 0.45 Nm3 CH4/kg VS fed) combined with their higher areal biomass productivity make them particularly attractive as a feedstock for an anaerobic digestion-based biorefinery concept.

This study investigates the influence of anode and cathode size and arrangement on hydrogen production in a membrane-less flat-plate microbial electrolysis cell (MEC). Protein measurements were used to evaluate microbial density in the carbon felt anode. The protein concentration was observed to significantly decrease with the increase in distance from the anode–cathode interface. Cathode placement on both sides of the carbon felt anode was found to increase the current, but also led to increased losses of hydrogen to hydrogenotrophic activity leading to methane production. Overall, the best performance was obtained in the flat-plate MEC with a two-layer 10 mm thick carbon felt anode and a single gas-diffusion cathode sandwiched between the anode and the hydrogen collection compartments.

The objective of the present study was to investigate the optimal nutritional requirements for hydrogen production from carbon monoxide by biological water-gas shift (WGS) reaction with Carboxydothermus hydrogenoformans using orthogonal layout methods. Cultures of C. hydrogenoformans on the medium as formulated by the strain supplier (Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH) unexpectedly showed a large content in inorganic material. This was confirmed by the rather elevated levels of calcium and phosphorus contained in the grown biomass. As an excessive production of those minerals may interfere with the growth and catabolism rates as well as clog up biofilm-based reactors, it was desirable to minimize the mineral accumulation during growth, while keeping at maximal levels both the H2 yield and the specific H2 production rate (SHPR). PO 4 3 − , HCO 3 − , Ca2+ and Mg2+ were considered as potentially the major factors of the mineral accumulation. The experiments were designed according to the Taguchi’s orthogonal method, using the above factors at three levels, and considering the culture mineral content, the H2 yield and the SHPR as optimization criteria. Optimal concentrations of PO 4 3 − , HCO 3 − , Ca2+ and Mg2+ were determined as (mM): 1.0, 5.0, 0.1 and 0.5, respectively. Under those culture conditions, Ca + P content decreased from 55.6 ± 1.8 to 9.5 ± 3% while the highest H2 yield at 90.9 ± 1.2% and SHPR at 0.85 ± 0.06 mol H2 g−1 VSS d−1 were achieved in bottle batch tests at 100% CO headspace atmosphere, neutral pH, a temperature of 70 °C, and an agitation of 100 rpm.

The objective of this study was to improve the biological water-gas shift reaction for producing hydrogen (H2) by conversion of carbon monoxide (CO) using an anaerobic thermophilic pure strain, Carboxydothermus hydrogenoformans. Specific hydrogen production rates and yields were investigated at initial biomass densities varying from 5 to 20 mg volatile suspended solid (VSS) L-1. Results showed that the gas-liquid mass transfer limits the CO conversion rate at high biomass concentrations. At 100-rpm agitation and at CO partial pressure of 1 atm, the optimal substrate/biomass ratio must exceed 5 mol CO g-1 biomass VSS in order to avoid gas-liquid substrate transfer limitation. An average H2 yield of 94±3% and a specific hydrogen production rate of ca. 3 mol g-1 VSS day-1 were obtained at initial biomass densities between 5 and 8 mg VSS-1. In addition, CO bioconversion kinetics was assessed at CO partial pressure from 0.16 to 2 atm, corresponding to a dissolved CO concentration at 70°C from 0.09 to 1.1 mM. Specific bioactivity was maximal at 3.5 mol CO g-1 VSS day-1 for a dissolved CO concentration of 0.55 mM in the culture. This optimal concentration is higher than with most other hydrogenogenic carboxydotrophic species. © 2011 Her Majesty the Queen in Right of Canada.

Herbivorous mammals and wood-eating insects are fairly effective in the digestion of plant polymers, such as lignocellulosics. In order to improve methane production from the lignocellulosic biomass, several kinds of anaerobic digestion processes derived from animal models have been devised. However, the rates of biodegradation occurring in the anaerobic bioreactors still remain lower than in animal guts. The effectiveness of the digestive systems of those animals results from the concerted action of the various enzymes (e.g. cellulases, xylanases, esterases, ligninases) produced in their guts as well as their integration with mechanical and chemical actions. Powerful pretreatment (prefermentation) operations are integrated to and support efficiently the microbial fermentation system, e.g. the rumination (i.e. mechanical) in ruminants and the secretion of endogenous cellulases (i.e. enzymatic) or the alkaline treatment (chemical) at mid-way in xylophagous insects. The oxygen gradients along the gastrointestinal tract may also stimulate the hydrolytic activities of some microbial populations. In addition, the solid retention time, the digesta flow and the removal of the end-products are well ordered to enable animals to thrive on a complex polymer such as lignocellulose. At the same time, technologies were developed to degrade lignocellulosic biomass, such as the rumen derived anaerobic digestion (RUDAD) process and the rumen simulating technique (RUSITEC), more elaborated and using rumen microbial consortia. Overall, they showed that the fermentation taking place in the rumen fermentation and even in the hindgut are biological processes that go beyond the limited environmental conditions generally found in anaerobic digesters. Hence, knowledge on herbivores' digestion mechanisms might be better exploited in the design and operation of anaerobic digesters. This literature review is a cross-analysis of the relevant information about the digestive strategies of herbivorous and wood-eating animals and the bioengineering techniques in lignocelluloses degradation. The aim is to highlight strategies of animals' digestion simulation for more effective anaerobic digestion of lignocellulosic compounds and other solid residues. © 2010 Her Majesty.

Electricity generation in a microbial fuel cell (MFC) using carbon monoxide (CO) or synthesis gas (syngas) as a carbon source has been demonstrated recently. A major challenge associated with CO or syngas utilization is the mass transfer limitation of these sparingly soluble gases in the aqueous phase. This study evaluated the applicability of a dense polymer silicone membrane and thin wall silicone tubing for CO mass transfer in MFCs. Replacing the sparger used in our previous study with the membrane systems for CO delivery resulted in improved MFC performance and CO transformation efficiency. A power output and CO transformation efficiency of up to 18 mW LR-1 (normalized to anode compartment volume) and 98%, respectively, was obtained. The use of membrane systems offers the advantage of improved mass transfer and reduced reactor volume, thus increasing the volumetric power output of MFCs operating on a gaseous substrate such as CO. © 2011 Elsevier Ltd. All rights reserved.

The owners of farm-scale anaerobic digesters are relying on off-farm wastes or energy crops as a co-digestion feedstock with animal manure in order to increase their production of methane and thus revenues. Switchgrass represents an interesting feedstock for Canadian digesters owners as it is a high-yielding low-maintenance perennial crop, well adapted to northern climate. Methane potential assays in batch tests showed methane production of 19.4 ± 3.6, 28.3 ± 1.7, 37.3 ± 7.1 and 45.7 ± 0.8 L kg(-1), for raw manure, blended manure, manure and mulched switchgrass, manure and pretreated switchgrass, respectively. Two 6-L lab-scale anaerobic digesters were operated for 130 days in order to assess the benefit of co-digesting switchgrass with bovine manure (digester #2), at a 20% wet mass fraction, compared with a manure-only operation (digester #1) The digesters were operated at an hydraulic retention time of 37 ± 6 days and at loads of 2.4 ± 0.6 and 2.6 ± 0.6 kg total volatile solids (TVS) L(-1) day(-1) for digesters #1 (D1) and #2 (D2), respectively. The TVS degradation reached 25 and 39%, which resulted in a methane production of 1.18 ± 0.18 and 2.19 ± 0.31 L day(-1) for D1 and D2, respectively. The addition of 20% on a wet mass ratio of switchgrass to a manure digester increased its methane production by 86%. The co-digestion of switchgrass in a 500 m(3) manure digester could yield up to 10.2 GJ day(-1) of purified methane or 1.1 MWh day(-1) of electricity.

Gasification of biomass produces a mixture of gas (mainly carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen (H(2))) called synthesis gas, or syngas, by thermal degradation without combustion. Syngas can be used for heat or electricity production by thermochemical processes. This project aims at developing an alternative way to bioupgrade syngas into biogas (mainly methane), via anaerobic fermentation. Nonacclimated industrial granular sludge to be used as reactor inoculum was initially evaluated for mesophilic carboxydotrophic methanogenesis potential in batch tests at 4 and 8 mmol CO/g VSS.d, in the absence and presence of H(2) and CO(2), respectively. Granular sludge was then introduced into a 30 L gas-lift reactor and supplied with CO, to study the production of methane and other metabolites, at different gas dilutions as well as feeding and recirculation rates. A maximal CO conversion efficiency of 75%, which was gas-liquid mass transfer limited, occurred at a CO partial pressure of 0.6 atm combined with a gas recirculation ratio of 20:1. The anaerobic granule potential for methanogenesis from CO was likely hydrogenotrophic, combined with CO-dependent H(2) formation, either under mesophilic or thermophilic conditions. Thermophilic conditions provide the anaerobic granules with a CO-bioconversion potential significantly larger (5-fold) than under mesophilic conditions, so long as the gas-liquid transfer is alleviated.

Catalysts for the oxygen reduction reaction (ORR) in a microbial fuel cell (MFC) were prepared by the impregnation on carbon black of Fe II acetate (FeAc), Cl–Fe III tetramethoxyphenyl porphyrin (ClFeTMPP), and Fe II phthalocyanine (FePc). These materials were subsequently pyrolyzed at a high temperature. The ORR activity of all Fe-based catalysts was measured at pH 7 with a rotating disk electrode (RDE) and their performance for electricity production was then verified in a continuous flow MFC. Catalysts prepared with FeAc and pyrolyzed in NH 3 showed poor activity in RDE tests as well as a poor performance in a MFC. The ORR activity and fuel cell performance for catalysts prepared with ClFeTMPP and FePc and pyrolyzed in Ar were significantly higher and comparable for both precursors. The iron loading was optimized for FePc-based catalysts. With a constant catalyst load of 2 mg cm −2 in a MFC, the highest power output (550–590 mW/m 2 ) was observed when the Fe content was 0.5–0.8 wt%, corresponding to only 0.01–016 mg Fe/cm 2 . A similar power output was observed using a Pt-based carbon cloth cathode containing 0.5 mg Pt/cm 2 . Long-term stability of the Fe-based cathode (0.5 wt% Fe) was confirmed over 20 days of MFC testing.

研究了在中空纤维膜生物反应器(MBR)内利用合成气中的CO作为碳源连续发酵制氢的性能。厌氧发酵菌C.hydrogenoformans应用于生物催化合成气发酵制氢反应中，可把CO和H2O直接转化为CO2和H2。在MBR内连续厌氧发酵，分别考察了不同CO进料载荷和液相循环量对反应器产氢性能的影响。实验结果表明，在CO进料载荷为0.22 mol/d、液相循环量为1500mL/min时，分别得到最大的CO转化率97.6%和产氢速率0.46mol/d，产氢得率保持在90%以上，同时计算得到膜生物反应器中的气液传质系数为1.72h-1

The dissolved hydrogen concentration was monitored in four laboratory-scale upflow sludge bed reactors. The upflow velocity (v UP ) differed in each reactor, providing different hydraulic regimes. Five pseudo-steady-state conditions were applied to the four reactors. The dissolved hydrogen concentration increased proportionally with the organic loading rates (OLR) of the reactors, to attain values as high as 20 μM, while still remaining independent of the hydraulic regime. The experimental data yielded low hydrogen mass-transfer rates (k L a) and high ratios of the measured dissolved hydrogen concentration value to the equilibrium value calculated from the hydrogen partial pressure in the gas phase (sursaturation factor): from 0.04 to 0.46 h −1 , and from 19 to 102, respectively.

The methane produced from the anaerobic digestion of organic wastes and energy crops represents an elegant and economical means of generating renewable biofuel. Anaerobic digestion is a mature technology and is already used for the conversion of the organic fraction of municipal solid wastes and excess primary and secondary sludge from waste-water treatment plants. High methane yield up to 0.45 m3 STP CH4/kg volatile solids (VS) or 12 390 m3 STP CH4/ ha can be achieved with sugar and starch crops, although these cultures are competing with food and feed crops for high-quality land. The cultivation of lignocellulosic crops on marginal and set-aside lands is a more environmentally sound and sustainable option for renewable energy production. The methane yield obtained from these crops is lower, 0.17–0.39 m3 STP CH4/kg VS or 5400 m3 STP CH4/ha, as its conversion into methane is facing the same initial barrier as for the production of ethanol, for example, hydrolysis of the crops. Intensive research and development on efficient pre-treatments is ongoing to optimize the net energy production, which is potentially greater than for liquid biofuels, since the whole substrate excepted lignin is convertible into methane. Copyright © 2010 Crown in the right of Canada

Increasing demand for the production of renewable fuels has recently generated a particular interest in microbial production of butanol. Anaerobic bacteria, such as Clostridium spp., can naturally convert carbohydrates into a variety of primary products, including alcohols like butanol. The genetics of microorganisms like Clostridium acetobutylicum have been well studied and their solvent-producing metabolic pathways characterized. In contrast, less is known about the genetics of Clostridium spp. capable of converting syngas or its individual components into solvents. In this study, the type of strain of a new solventogenic Clostridium species, C. carboxidivorans, was genetically characterized by genome sequencing. C. carboxidivorans strain P7(T) possessed a complete Wood-Ljungdahl pathway gene cluster, involving CO and CO(2) fixation and conversion to acetyl-CoA. Moreover, with the exception of an acetone production pathway, all the genetic determinants of canonical ABE metabolic pathways for acetate, butyrate, ethanol and butanol production were present in the P7(T) chromosome. The functionality of these pathways was also confirmed by growth of P7(T) on CO and production of CO(2) as well as volatile fatty acids (acetate and butyrate) and solvents (ethanol and butanol). P7(T) was also found to harbour a 19 Kbp plasmid, which did not include essential or butanol production related genes. This study has generated in depth knowledge of the P7(T) genome, which will be helpful in developing metabolic engineering strategies to improve C. carboxidivorans's natural capacity to produce potential biofuels from syngas.