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International audience; Granulation of biomass is at the basis of the operation of the most successful anaerobic systems (UASB, EGSB and IC reactors) applied worldwide for wastewater treatment. Despite of decades of studies of the biomass granulation process, it is still not fully understood and controlled. Degranulation/lack of granulation^ is a problem that occurs sometimes in anaerobic systems resulting often in heavy loss of biomass and poor treatment efficiencies or even complete reactor failure. Such a problem occurred in Mexico in two full-scale UASB reactors treating cheese wastewater. A close follow-up of the plant was performed to try to identify the factors responsible for the phenomenon. Basically, the list of possible causes to a granulation problem that were investigated can be classified amongst nutritional, i.e. related to wastewater composition (e.g. deficiency or excess of macro- nutrients or micronutrients, too high COD proportion due to proteins or volatile fatty acids, high ammonium, sulphate or fat concentrations), operational (excessive loading rate, sub- or over-optimal water upflow velocity) and structural (poor hydraulic design of the plant). Despite of an intensive search, the causes of the granulation problems could not be identified. The present case remains however an example of the strategy that must be followed to identify these causes and could be used as a guide for plant operators or consultants who are confronted with a similar situation independently of the type of wastewater. According to a large literature based on successful experiments at lab scale, an attempt to artificially granulate the industrial reactor biomass through the dosage of a cationic polymer was also tested but equally failed. Instead of promoting granulation, the dosage caused a heavy sludge flotation. This shows that the scaling of such a procedure from lab to real scale cannot be advised right away unless its operability at such a scale can be demonstrated.

The effect of pH control (4, 5, 6, 7) on volatile fatty acids (VFA) production from food waste was investigated in a leach bed reactor (LBR) operated at 50 °C. Stabilisation of pH at 7 resulted in hydrolysis yield of 530 g soluble chemical oxygen demand (sCOD)/kg total volatile solids (TVS) added and VFA yield of 247 g COD/kg TVS added, which were highest among all pH tested. Butyric acid dominated the VFA mix (49–54%) at pH of 7 and 6, while acetate composed the primary VFA (41–56%) at pH of 4 and 5. A metabolic shift towards lactic acid production was observed at pH of 5. Improving leachate recirculation rate further improved the hydrolysis and degradation efficiency by 10–16% and the acidification yield to 340 g COD/kg TVS added. The butyric acid concentration of 16.8 g/L obtained at neutral pH conditions is among the highest reported in literature.

This study compared the acidogenic fermentation of Scenedesmus sp.-AMDD at laboratory-scale, under mesophilic (35 °C) and thermophilic conditions (55 °C). Preliminary batch tests were performed to evaluate best conditions for volatile fatty acid (VFA) production from microalgal biomass, with respect to the inoculum, pH and nutrients. The use of bovine manure as inoculum, the operating pH of 4.5 and the addition of a nutrient mix, resulted in a high VFA production of up to 222 mg g-1 total volatile solid (TVS), with a butyrate share of 27%. Both digesters displayed similar hydrolytic activity with 0.38±0.02 and 0.42±0.03 g soluble chemical oxygen demand (COD) g-1 TVS for the digesters operated at 35 and 55 °C, respectively. Mesophilic conditions were more favourable for VFA production, which reached 171±5, compared to 88±12 mg soluble COD g-1 TVS added under thermophilic conditions (94% more). It was shown that in both digesters, butyrate was the predominant VFA.

Syngas generated by thermal gasification of biomass or coal can be steam reformed and purified into methane, which could be used locally for energy needs, or re-injected in the natural gas grid. As an alternative to chemical catalysis, the main components of the syngas (CO, CO2, and H2) can be used as substrates by a wide range of microorganisms, to be converted into gas biofuels, including methane. This study evaluates the carboxydotrophic (CO-consuming) methanogenic potential present in an anaerobic sludge from an upflow anaerobic sludge bed (UASB) reactor treating waste water, and elucidates the CO conversion routes to methane at 35 ± 3°C. Kinetic activity tests under CO at partial pressures (pCO) varying from 0.1 to 1.5 atm (0.09–1.31 mmol/L in the liquid phase) showed a significant carboxydotrophic activity potential for growing conditions on CO alone. A maximum methanogenic activity of 1 mmol CH4 per g of volatile suspended solid and per day was achieved at 0.2 atm of CO (0.17 mmol/L), and then the rate decreased with the amount of CO supplied. The intermediary metabolites such as acetate, H2, and propionate started to accumulate at higher CO concentrations. Inhibition experiments with 2-bromoethanesulfonic acid (BES), fluoroacetate, and vancomycin showed that in a mixed culture CO was converted mainly to acetate by acetogenic bacteria, which was further transformed to methane by acetoclastic methanogens, while direct methanogenic CO conversion was negligible. Methanogenesis was totally blocked at high pCO in the bottles (≥1 atm). However it was possible to achieve higher methanogenic potential under a 100% CO atmosphere after acclimation of the sludge to CO. This adaptation to high CO concentrations led to a shift in the archaeal population, then dominated by hydrogen-utilizing methanogens, which were able to take over acetoclastic methanogens, while syntrophic acetate oxidizing (SAO) bacteria oxidized acetate into CO2 and H2. The disaggregation of the granular sludge showed a negative impact on their methanogenic activity, confirming that the acetoclastic methanogens were the most sensitive to CO, and a contrario, the advantage of using granular sludge for further development toward large-scale methane production from CO-rich syngas.

Interest in the use of microalgae for the production of biofuels has grown in recent years. Biomethane is a biofuel that can be obtained with high efficiency from anaerobic digestion of various organic feedstocks. In this study, a selection of freshwater (n = 15) and marine (n = 5) microalgae were tested in order to identify a microalgal strain that could be used as a model for large scale production of methane. Analysis of pH, volatile suspended solids and ammonium at the end of the assay ranged between 6.98–7.66, 16.0–25.9 g/L and 495–1622 mg/L respectively. No significant differences in these values were detected between freshwater and marine strains. There was no significant difference in the methane yield from freshwater microalgae (329 ± 43 mL CH4/g TVS) and marine microalgae (298 ± 83 mL CH4/g TVS) although it varied greatly within the tested strains. A statistical analysis of the microalgae grown under two different culture media showed that the type of medium was more determinant than the type of microalgae (freshwater or marine) for the methane yield, with 310 ± 35, 365 ± 25 and 303 ± 77 mL CH4/g TVS for the freshwater microalgae grown in Bold’s-3NV, f/2 and marine microalgae grown in f/2 media, respectively. The strains Scenedesmus sp.-AMDD, Isochrysis sp. and Scenedesmus dimorphus displayed the best methane yield with 410 ± 6, 408 ± 4 and 397 ± 10 mL CH4/g TVS, respectively. The strain Scenedesmus sp.-AMDD was chosen as a model strain for future work development with continuously fed digesters.

Biomethane production from the microalga Scenedesmus sp. AMDD was demonstrated in an upflow anaerobic sludge bed (UASB) reactor. A full factorial design experiment was used to identify the effect of organic loading rate (OLR) of algal biomass and hydraulic retention time (HRT) on the volumetric rate of methane production. At an HRT of 4 days and an OLR of 3.23 gTVS LR− 1 d− 1 corresponding to an influent microalgae concentration of 12 g total volatile solids (TVS) L− 1, the volumetric rate of CH4 production reached 0.6 LSTP L− 1R d− 1. A methane yield of 0.18–0.2 L per gTVS of fed microalgae was estimated. A stable performance was observed throughout 3 months of UASB reactor operation. Due to the short HRT and the good performance of UASB reactor, operated at influent microalgae concentrations in a range of 4–12 gTVS L− 1, this reactor type is suitable for coupling with photobioreactors equipped with gravitational settlers.

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.

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.

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.

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.

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.

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.

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

Electricity production from carbon monoxide (CO) is demonstrated in a single chamber microbial fuel cell (MFC) with a CoTMPP-based air cathode. The MFC was inoculated with anaerobic sludge and continuously sparged with CO as a sole carbon source. Volumetric power output was maximized at a CO flow rate of 4.8LLR(-1)d(-1) reaching 6.4mWLR(-1). Several soluble and gaseous degradation products including hydrogen, methane, and acetate were detected, resulting in a relatively low apparent Coulombic efficiency of 8.7%. Tests also demonstrated electricity production from hydrogen and acetate with the highest and fastest increase in voltage exhibited after acetate injection. It is hypothesized that electricity generation in a CO-fed MFC is accomplished by a consortium of carboxydotrophic and carbon monoxide - tolerant anodophilic microorganisms.

Gas diffusion cathodes with electrodeposited nickel (Ni) particles have been developed and tested for hydrogen production in a continuous flow microbial electrolysis cell (MEC). A high catalytic activity of electrodeposited Ni particles in such a MEC was obtained without a proton exchange membrane, i.e. under direct cathode exposure to anodic liquid. Co-electrodeposition of Pt and Ni particles did not improve any further hydrogen production. The maximum hydrogen production rate was 5.4 L/LR/day, corresponding to Ni loads between 0.2 and 0.4 mg cm−2. Continuous MEC operation demonstrated stable hydrogen production for over one month. Owing to the fast hydrogen transport through the cathodic gas diffusion layer, the loss of hydrogen production to methanogenic activity was minimal, generally with less than 5% methane in the off-gas. Overall, gas diffusion cathodes with electrodeposited Ni particles demonstrated excellent stability for hydrogen production compared to expensive Pt cathodes.

Gas diffusion cathodes with Ni alloy and Ni catalysts manufactured by chemical deposition were tested for H2 production in a microbial electrolysis cell (MEC). In a continuous flow MEC, multi-component cathodes containing Ni, Mo, Cr, and Fe, at a total catalyst load of 1 mg cm−2 on carbon support demonstrated stable H2 production at rates of 2.8 – 3.7 L L R − 1 d − 1 with only 5% methane in the gas stream. Furthermore, a Ni-only gas diffusion cathode, with a Ni load of 0.6 mg cm−2, demonstrated a H2 production rate of 4.1 L L R − 1 d − 1 . Overall, H2 production was found to be proportional to the Ni load implying that inexpensive gas diffusion cathodes prepared by chemical deposition of Ni can be successfully used for continuous production of H2 in a MEC.

Anaerobic digestion of manures induces deodorization and conserves nitrogen. Livestock producers could transform their long-term (250–300 day) manure storages into psychrophilic anaerobic digesters, thus greatly reducing the investment, operational and technical cost associated with the treatment. But, sufficient inoculation is required and the feeding regime differs from that of a fixed volume digester, as the fed manure volume to digester content ratio is ever decreasing over time and the retention time is as long as the storage period. The project was designed to establish, in the laboratory, the inoculation conditions and feeding regime leading to the efficient establishment and operation of anaerobic digestion in conventional storages. In the laboratory using the biochemical methane potential test (BMP), methane production was monitored from swine manure inoculated with one of the three inocula (cattle manure—B; municipal wastewater anaerobic sludge—R, and; food processing wastewater anaerobic sludge—C) at four ratios (0, 10, 30 and 50%). Also, six prototype digesters were used to simulate VSS digestion in conventional storages, under two feeding regimes (once every week and every 2 weeks) and using three inocula. With the BMP and for all three inocula, a ratio of 10% provided the fastest initiation and the highest methane production. Both R and C initiated methane production as of the 1st day because of their active bacterial population, while B, obtained from a facultative system, required 24 days. After 100 days, all three inocula had produced the same amount of methane, for the same inoculation ratio. In the prototype digesters, both R and C inocula produced methane as of the first day, while the B inoculum produced methane after day 45 and 78 days, for the 1/week and 1/2week feeding regime, respectively. For both feeding regimes and after 148 days, all three inocula produced the same cumulative amount of methane. Thus, 10% B can initiate anaerobic conditions in swine manure during storage, as long as the storage period exceeds 140 days and a 45 day initiation period at a temperature is 35 °C.

Hydrogen production from glycerol was studied in a microbial electrolysis cell (MEC) with a 250 mL anodic chamber and a gas-phase cathode. A membraneless MEC design was employed, where a graphite felt anode and gas diffusion cathode were only separated by a 0.7 mm thick highly porous synthetic fabric (J-cloth). Glycerol (fuel) was continuously fed to the anodic chamber at loads of 0.3-5.3 g La⁻¹ d⁻¹. Fast conversion of glycerol to fermentation products, mainly 1,3-propanediol, propionate, and acetate was observed, that is, the fermentation products rather than glycerol were the most likely source of electrons for the anodophilic microorganisms. Hydrogen formation at the cathode required additional input of energy, which was provided by a controllable power supply. Hydrogen formation was observed starting from an applied voltage of 0.5 V. The highest volumetric rate of hydrogen production was 0.6 L La⁻¹ d⁻¹, which was obtained at a glycerol load of 2.7 gLa⁻¹ d⁻¹ and an applied voltage of 1.0 V. Hydrogen yield reached 5.4 mol per mol glycerol consumed, which corresponded to 77% of the theoretical value.

Anaerobic granule nuclei enriched in either acidogens (AF), syntrophic consortia (SN), Methanosaeta spp. (MT) and Methanosarcina spp. (MN) were developed in four upflow bed filter reactors fed with sucrose, an ethanol/acetate mixture, acetate and methanol, respectively. The four developed granule nuclei presented different settling velocities: 3.2, 8.7, 10.5 and 11.3 m/h for the AF flocs, the MS-, the SN- and the MT-nuclei, respectively. The ash content represented 60%, 40%, 30% and 16% of dry weight for the MT-, MS-, SN-enriched nuclei, and AF flocs, respectively. Acidogenic flocs contained high amount of extracellular polymeric substances. The influence of these four different nuclei on the time course of complex granule development was investigated by shifting the feed carbon of all of the four reactors to sucrose. Granulation proceeded rapidly both on syntrophic and Methanosaeta nuclei. The largest granules (Sauter diameter of 2.36 mm), however, were obtained within the shortest period in the reactor started with syntrophic nuclei. These nuclei presented also the best colonization by fermentative bacteria as shown by the evolution of their glucotrophic activities. Less satisfying granulation was obtained on Methanosarcina nuclei. In contrast, granulation was significantly retarded when acidogens were used as precursors. From these results it appears that syntrophs and Methanosaeta spp. play the principal role in anaerobic granulation process.

This study demonstrates hydrogen production in a membrane-less continuous flow microbial electrolysis cell (MEC) with a gas-phase cathode. The MEC used a carbon felt anode and a gas diffusion cathode with a Pt loading of 0.5 mg cm−2. No proton exchange membrane (PEM) was used in the setup. Instead, the electrodes were separated by a J-cloth. The absence of a PEM as well as a short distance maintained between the electrodes (0.3 mm) resulted in a low internal resistance of 19 Ω. Due to an improved design, the volumetric hydrogen production rate reached 6.3 LSTP L A − 1 d−1. In spite of the PEM absence, methane concentration in the gas collection chamber was below 2.1% and the presence of hydrogen in the anodic chamber was never observed.

A strain of Mycobacterium austroafricanum capable of mineralizing methyl tert-butyl ether (MtBE) as its sole carbon and energy source had previously been isolated from activated sludge. The use of this bacteria in a biobarrier system for the in situ treatment of contaminated groundwater was the ultimate goal of this work. This paper reports the results of initial studies to find an appropriate immobilizing or support material. Several materials (peat, perlite, pozzolan, pumice and granulated activated carbon) were considered. Selection was based on the measurement and comparison of their abilities to immobilize or retain the bacteria, and to adsorb MtBE. The immobilization test was based on monitoring the respiration of bacteria remaining on the material after initial contact times of either 24 or 72 h. O2 consumption and CO2 production were measured over a period of time. The study showed that perlite was the best material. Adsorption isotherms for MtBE were constructed for each support. The strength of adsorption coefficient, Kf, in the Freundlich equation was calculated and used as the basis for comparison of their adsorptive capacities. The strength of adsorption was highest for the granulated activated carbon, and the Kf values for the other materials were relatively low and fell within the same range. However, since GAC performed poorly in the immobilization test, perlite was selected as the best support material.

This study presents a temperature-based control strategy for the stabilization of an anaerobic reactor during organic overloads. To prove feasibility of the proposed approach the rate of methane production was followed in batch activity tests and reactor runs during mesophilic-thermophilic transitions. Within the first 0.25-6 h of temperature augmentation, an increase in the rate of methane production was observed with higher rates measured under thermophilic (above 40 degrees C) conditions. However, 24 h after startup both in batch tests and reactor runs, the rate of methane production under thermophilic conditions was inferior to that under optimal mesophilic conditions (35 degrees C). Following these results, a control strategy based on short-term augmentation of the reactor temperature was proposed and tested in a 10 L UASB reactor. The control strategy employed a multi-model observer-based estimator to stabilize the effluent COD concentration during organic overloads. The temperature-based control resulted in an increased methanization rate and improved reactor stability overall.

A proof of concept was performed in order to verify if the coupling of anaerobic and aerobic conditions inside the same digester could efficiently treat a reconstituted whey wastewater at 21 degrees C. The sequencing batch reactor (SBR) cycles combined initial anaerobic phase and final aerobic phase with reduced aeration. A series of 24 h cycles in 0.5 L digesters, with four different levels of oxygenation (none, 54, 108 and 182 mgO2 per gram of chemical oxygen demand (COD)), showed residual soluble chemical oxygen demand (sCOD) of 683 +/- 46, 720 +/- 33, 581 +/- 45, 1239 +/- 15 mg L(-1), respectively. Acetate and hydrogen specific activities were maintained for the anaerobic digester, but decreased by 10-25% for the acetate and by 20-50% for the hydrogen, in the coupled digesters. The experiment was repeated using 48 h cycles with limited aeration during 6 or 16 hours at 54 and 108 mgO2gCODinitial(-1), displaying residual sCOD of 177 +/- 43, 137 +/- 38, 104 +/- 22 and 112 +/- 9 mgL(-1) for the anaerobic and the coupled digesters, respectively. The coupled digesters recovered after a pH shock with residual sCOD as low as 132 mg L(-1) compared to 636 mg L(-1) for the anaerobic digester. With regard to the obtained results, the feasibility of the anaerobic-aerobic coupling in SBR digesters for the treatment of whey wastewater was demonstrated.

In this study, a two-compartment continuous flow microbial fuel cell (MFC) reactor was used to compare the efficiencies of cathode oxygenation by air and by hydrogen peroxide. The MFC reactor had neither a proton-selective membrane nor an electron transfer mediator. At startup, the cathodic compartment was continuously aerated and the anodic compartment was fed with a glucose solution. An increase of electrical power generation from 0.008 to 7.2 mW m(-2) of anode surface with a steady-state potential of 215-225 mV was observed within a period of 12 days. The performance of the air-oxygenated MFC reactor progressively declined over time because of biofilm proliferation in the cathodic compartment. Oxygenation of the cathodic compartment using 300 mL d(-1) of 0.3% hydrogen peroxide solution resulted in a power density of up to 22 mW m(-2) (68.2 mA m(-2)) of anode surface at a potential of 340-350 mV. The use of H2O2 for oxygenation was found to improve the long-term stability of the MFC reactor.

In this work, the axial distribution of a conservative tracer in the upflow anaerobic sludge bed (UASB) reactor was modelled by a two-compartment model describing sludge bed and liquid zones. The orthogonal collocation algorithm was used for numerical solution of the model. The model parameters were estimated using on-line fluorescence-based measurements of an inert tracer rhodamine. Rhodamine concentrations were simultaneously measured at the bottom, middle and top of the sludge bed, as well as in the reactor effluent. The model used either a constant or variable axial dispersion coefficient in the sludge bed zone. A significantly better agreement between model outputs and observed tracer distribution was obtained when the dispersion coefficient was proportional to a constant raised to the power of the reactor height. In addition, a near linear dependence of the dispersion coefficient on the liquid upflow velocity was found. These findings, along with high efficiency of the orthogonal collocation algorithm used for model solution, enable future development of a comprehensive model, which accounts for both hydraulics and biokinetics of the anaerobic digestion process.

O. TRESSE, F. MOUNIEN, M.-J. LEVESQUE AND S. GUIOT. 2004. Aims: To understand the microbial ecology underlying trichloethene (TCE) degradation in a coupled anaerobic/ aerobic single stage (CANOXIS) reactor oxygenated with hydrogen peroxide (H2O2) and in an upflow anaerobic sludge bed (UASB) reactor. Methods and Results: The molecular study of the microbial population dynamics and a phylogenetic characterization were conducted using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR- DGGE). In both reactors, TCE had a toxic effect on two uncultured bacterial populations whereas oxygen favoured the growth of aerobic species belonging to Rhizobiaceae and Dechloromonas. No methanotrophic bacteria were detected when targeting 16S rRNA gene with universal primers. Alternatively, pmo gene encoding the particulate methane monooxygenase of Methylomonas sp. LW21 could be detected in the coupled reactor when H2O2 was supplied at 0AE 7gO 2 l � 1 R day )1 . Conclusions: Methylomonas sp. LW21 that could be responsible for the aerobic degradation of the TCE by- products is not among the predominant bacterial populations in the coupled reactor. It seems to have been outcompeted by heterotrophic bacteria (Rhizobiaceae and Dechloromonas sp.) for oxygen. Significance and Impact of the Study: The results obtained show the limitations of the coupled reactor examined in this study. Further investigations should focus on the operating conditions of this reactor in order to favour the growth of the methanotrophs.

This study presents a comparison of denitrification rates and denitrification stoichiometry when using different sources of carbon. Denitrification tests were carried out in test bottles containing water and soil samples acquired at a nitrate-contaminated site and supplemented with either sucrose, acetate or ethanol. The tests demonstrated nitrate removal in all carbon source supplemented bottles. The rate of denitrification and the required amount of a carbon source, however, depended on the choice of substrate. Ethanol and acetate were found to provide the highest denitrification rate, that of 1.4 - 1.6 mg-N l(-1) d(-1). Sucrose-supplemented bottles demonstrated a significantly slower denitrification rate, that of 0.6 - 0.9 mg-N l(-1) d(-1). In addition to slow denitrification rates, sucrose-supported denitrification required more carbon source.

Controlling the mean diameter of polymeric carriers is crucial to the successful application of encapsulated cells for in situ bioaugmentation of contaminated aquifers. The cell carriers should be small enough to be transported through a granular soil matrix, thus an emulsification-internal gelation technique for production of cell-encapsulating gellan gum microbeads is proposed. Mean diameter and size distribution of microbeads were investigated as a function of the water-in-oil emulsion parameters. The mean diameter of the microbeads ranged from 12 to 135 μm, varying as a descending function of the stirring rate (1000–5500 rpm) and emulsifier concentration (0–0.20% w/w), and as an ascending function of the disperse phase volume fraction (0.08–0.25). A bacterial consortium encapsulated within the microbeads (23 μm mean diameter) showed improved biodegradation activity in the removal of gasoline (400 mg L −1 ), as compared to free cells. A high degree of repeatability in the microbead formation process and particle size measurements was demonstrated. The results of this study suggest that the emulsification process can potentially be used for the large-scale production of controlled-diameter gellan gum-encapsulated cell microbeads for subsurface bioremediation applications.

A laboratory-scale permeable biobarrier exhibited high removal efficiencies of benzene at inlet concentrations of 0.4 to 35.1 mg/L and with a limited supply of dissolved oxygen. The supplied oxygen was less than the demand for a complete aerobic oxidation of benzene. Stainless steel pieces or granulated peat moss were used as packing material for microbial support in the biobarrier. Removal efficiencies ranged from 63.9% to 99.9% in the stainless steel-packed biobarrier and from 70.4% to 97.2% in the peat moss-packed biobarrier, while benzene elimination rate changed from 0.2 to 10.4 mg/L-d and from 0.1 to 3.7 mg/L-d in the two biobarriers, respectively. The consumption of sulfate and the presence of sulfate-reducing bacteria suggested the contribution of anaerobic metabolism in the biodegradation of benzene. The biodegradation of benzene under microaerophilic conditions (defined as dissolved oxygen concentrations

Native soil microbial populations and unadapted municipal anaerobic sludges were compared for nitramine explosive degradation in microcosm assays under various conditions. Microbial populations from an explosive-contaminated soil were only able to mineralize 12% hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) (at a concentration of 800 mg/kg slurry) or 4% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) (at a concentration of 267 mg/kg slurry). In contrast, municipal anaerobic sludges were able to mineralize them to carbon dioxide, with efficiencies of up to 65%. Reduction of RDX and HMX into their corresponding nitroso-derivatives was notably faster than their mineralization. The biodegradation of HMX was typically delayed by the presence of RDX in the microcosm, confirming RDX is used as an electron acceptor preferentially to HMX. The laboratory-scale bioslurry reactor reproduced the results of the microcosm assays, yet with much higher RDX and HMX degradation rates. A radiolabel-based mass balance in the soil slurry indicated that, besides a significant mineralization to carbon dioxide, 25% and 31% of RDX and HMX, respectively, appeared as acetonitrile-extractable metabolites, while the remaining part was incorporated into biomass and irreversibly bound to the soil matrix. About 10% of the HMX derivatives were estimated to be chemically bound to the soil matrix, while for RDX the estimation was nil.

International audience; The white-rot basidiomycete Phanerochaete chrysosporium BKM-F-1767 was tested for its capacity to degrade dehydroabietic acid (DHA). In anaerobic treatment, this molecule is the most recalcitrant member of the resin acid group, which is known to cause operational problems to anaerobic reactors treating pulp and paper industry wastewaters. In this study the effect of DHA on different parameters, such as growth, ligninolytic enzyme activity, extracellular protein production as well as both glycerol and ammonium consumption by the fungus, was determined. Although the above parameters were affected by the addition of DHA, the results show that the fungus could still produce significant titres of ligninolytic enzymes. The fungus removed 47% of the DHA initially present in the static culture, after 10 days of incubation. Anaerobic toxicity assays showed that the treatment of DHA with P. chrysosporium reduced the methanogenesis and acetogenesis inhibition caused by DHA and allowed improved methane production by the anaerobic bacteria.

As indicated in most literature reports, the solubility of pentachlorophenol (PCP) in water ranges between 10 and 20 mg l−1. Since PCP is a weak acid (pKa 4.35), its solubility increases drastically with increasing pH. When PCP dissolves in water two forms are normally present: undissociated PCP (PCP°) and a dissociated anionic form, i.e. pentachlorophenolate (PCP−). Both forms differ in their physico-chemical properties and in their microbial response and toxicity. It is therefore important to know the solubility behaviour of PCP at specific pHs when working with site remediation and toxicity assessment. While anionic PCP is very soluble, experimental data have shown that undissociated PCP has a solubility limited to 10 μM (3 mg l−1). Theoretical calculations have confirmed this value to be independent of the solution's pH. A non-empirical model was developed for estimating the “total” PCP aqueous solubility at different pHs using the standard solubility value and PCP's dissociation constant. The method may be extended to other chlorophenols and to most wastewaters.

The present study evaluates the capability of sulphonated lignin (S-lignin) and calcium to promote anaerobic sludge granulation, which is of prime importance in the operation of upflow anaerobic sludge bed (UASB)-like reactors. One of two reactors fed with a synthetic sugar waste was stepwise supplemented with a spent liquor rich in S-lignin from a neutral sulphite semi-chemical pulping plant to reach an addition rate of 0.17 g S-lignin per gram volatile suspended solid (VSS) per day. This resulted in biomass pre-granulation (50-60 % of the biomass aggregates had a size > 0.3 mm). No change was observed in the surface properties (hydrophobicity and zeta potential) of the bacterial aggregates. The S- lignin-fed sludge aggregated in an ordered and cluster-like manner and exhibited a more compact ultrastructure than the control sludge. Moreover, the addition of S-lignin slightly enhanced the metabolic activities of the biomass. Calcium ion addition following the S-lignin treatment improved the size and the settleability of the aggregates and increased the solid retention time. Key words

The ultrastructure of bacterial granules that were maintained in an upflow anaerobic sludge bed and filter reactor was examined. The reactor was fed a sucrose medium, and it was operated at 35 degrees C. Scanning and transmission electron microscopy revealed that the granular aggregates were three-layered structures. The exterior layer of the granule contained a very heterogeneous population that included rods, cocci, and filaments of various sizes. The middle layer consisted of a slightly less heterogeneous population than the exterior layer. A more ordered arrangement, made up predominantly of bacterial rods, was evident in this second layer. The third layer formed the internal core of the granules. It consisted of large numbers of Methanothrix-like cells. Large cavities, indicative of vigorous gas production, were evident in the third layer. On the basis of these ultrastructural results, a model that presents a possible explanation of granule development is offered.

The Gibbs free energy changes in methanogenic granular biomass from sludge-bed reactors were evaluated using the in situ concentrations and partial pressures of metabolites during the metabolism of acetate, hydrogen, formate and propionate. Based on mass balance calculations it appeared that the degradation of propionate into acetate, hydrogen and bicarbonate was endergonic, even if propionate was effectively degraded. On the other hand, the methane-producing reactions, both from acetate and from hydrogen plus bicarbonate, were found to be exergonic and the free energy change was sufficient for the formation of ATP. Formate was detected in only one of the two reactors. When formate, instead of hydrogen, was considered as the electron carrier between propionate-degrading and methanogenic bacteria, similar thermodynamic results were obtained. The existence of trophic microniches in the granular biomass is suggested to explain propionate degradation even though the Gibbs free energy change in the liquid surrounding the granules was positive. Hence, to make propionate degradation exergonic the dissolved hydrogen concentration surrounding the propionate-degrading bacteria would have to be about 30 times lower than in the free liquid.

A miniature fuel cell, using a hydrophobic Teflon(R) membrane, designed to continuously measure dissolved H(2) in nonbiological media, was tested for use in anaerobic digestion conditions. In water, this detector responds quickly and efficiently to variation of hydrogen concentration in the range from 80 to 770 nM The media used, and the metabolites or products found in anaerobic digestion media, i. e. inorganic carbon and phosphate buffers, formate, acetate, and dissolved methane, did not interfere with the signal of the detector cell. Dissolved hydrogen sulfide did not poison the cell but was detected. In spite of the detector's high sensitivity to hydrogen (about 21,000 times higher for hydrogen than for hydrogen sulfide), interferences can occur in media containing high sulfide levels.In a methanogenic reactor, the detector cell response to dissolved hydrogen was fast and reliable with time. The observed values ranged values ranged from 2 to 3.5 microM. Dissolved hydrogen concentrations were 40 to 70 times higher than values calculated from measured hydrogen partial pressures and Henry's coefficient, suggesting a limitation of the process in the hydrogen transfer from the liquid to the gaseous phase.

Mixing characteristics (using a radioactive tracer) and reactor performance of the upflow blanket filter (UBF) reactor operated at different loading rates (up to 32 kg chemical oxygen demand (COD) m⁻³ day⁻¹) were compared. The results indicated that mixing profiles of the reactor operated with effluent recirculation and without biomass were of the perfectly mixed type. Operation without recirculation resulted in about 18% dead space. The filter made of plastic rings and located in the top third of the reactor had no negative effect on reactor mixing. Operation at loading rates of up to 25 kg COD m⁻³ day⁻¹ permitted a soluble COD removal rate of 95% with a methane production rate of 5.9 m ³ m ⁻ ³ day ⁻ ¹. At higher loading rates, the efficiency of COD reduction decreased with a decrease of the specific acetoclastic activity to 0.5 kg acetate removed per kg volatile suspended solids (VSS) day⁻¹. At all loading rates studied it was observed that the performance was not related to the mixing characteristics, which had remained of the perfectly mixed type with an occasional small dead space (below 10%). The good mixing characteristics of the UBF reactor coupled with the high biomass content and the effective action of the filter make this reactor one of the most promising designs for the treatment of soluble wastes.