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Made available in DSpace on 2020-12-12T00:54:16Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Xylose is a by-product of lignocellulosic biomass processing for production of second-generation biofuels and could be suitable for bioproduct manufacturing. This paper describes an innovative approach that enables the system to achieve high yielding for hydrogen production. The study compared 4 physicochemical pre-treatments performed in an anaerobic mixed culture (acidic, thermal, acidic-thermal and thermal acidic) to achieve an inoculum with a high-efficiency xylose to hydrogen conversion under mesophilic conditions (30 °C). The acidic pre-treatment was the most efficient to select microorganisms able to produce hydrogen and volatile acid from xylose. Kinetics has shown that acidic pre-treatment had a hydrogen/xylose molar yielding factor of 1.57 (molar base) and a hydrogen maximum production rate of 253 mL H2 h−1. Mass balance considered all possible metabolic pathways using xylose as a substrate. Anaerobic degradation of ethanol was the most active pathway for hydrogen production in all experiments, except for the control. Each pre-treatment performed for the original inoculum resulted in different microbiological profiles, but the genus Clostridium was the most abundant in all assays. Acidic pre-treatment stimulated the growth of organisms from the genera Peptostreptococcaceae, Truepera and Kurthia, which could be related to the better results in hydrogen production found in this condition. Interdisciplinary Research Group on Biotechnology Applied to the Agriculture and the Environment School of Agricultural Engineering University of Campinas (GBMA/FEAGRI/UNICAMP), 501 Cândido Rondon Avenue, CEP, 13.083-875 Anaerobic Technologies and Bioprocess Control Group – Energy Mining and Environment Portfolio National Research Council Canada (CNRC/NRC), 6100 Royalmount Avenue Bioprocess and Biotechnology Department Faculty of Pharmaceutical Sciences of Araraquara Universidade Estadual Paulista “Júlio de Mesquita Filho” (FCFAR/UNESP) Km 01 - Campus Universitário, Araraquara-Jaú Road, CEP 14.801-902 Hydraulics and Sanitation Department São Carlos Engineering School Universidade de São Paulo (SHS/EESC/USP), Av. Trabalhador São-Carlense 400, CEP 13.566-590, São Carlos Bioprocess and Biotechnology Department Faculty of Pharmaceutical Sciences of Araraquara Universidade Estadual Paulista “Júlio de Mesquita Filho” (FCFAR/UNESP) Km 01 - Campus Universitário, Araraquara-Jaú Road, CEP 14.801-902

1AbstractThis work evaluates four different physicochemical pretreatments (acidic, thermal, acidic-thermal and thermal-acidic) on an anaerobic inoculum used for alcohol production from acetate and butyrate. All experiments were conducted in single batches using acetate and butyrate as substrates at 30 °C and with a pressurized headspace of pure H2 at 2.15 atm (218.2 MPa). Thermal and acidic-thermal pretreatments lead to higher production of both ethanol and butanol. Mathematical modelling shows that the highest attainable concentrations of ethanol and butanol produced were 122 mg L-1 and 97 mg L-1 for the thermal pretreatment (after 17.5 days) and 87 mg L-1 and 143 mg L-1 for the acidic-thermal pretreatment (after 18.9 days). Acetate was produced in all assays. Thermodynamic data indicated that a high H2 partial pressure favoured solventogenic metabolic pathways. Finally, sequencing data showed that both thermal and acidic-thermal pretreatments selected mainly the bacterial genera Pseudomonas, Brevundimonas and Clostridium. The acidic-thermal pretreatment selected a bacterial community more adapted to the conversion of acetate and butyrate into ethanol and butanol, respectively. Thermal-acidic pretreatment was unstable, showing significant variability between replicates. Acidic pretreatment showed the lowest alcohol production.

Direct interspecies electron transfer (DIET) has been typically proposed as mechanism of electron transfer among methanogenic populations in granules during anaerobic digestion where Geobacter species play a key role. Using anaerobic granules where Geobacteraceae members were not prevalent − representing only 0.3% of total bacteria −, tests incubated with two co-substrates showed that the rate of methanogenesis from formate and hydrogen diminished in the presence of a non-methanogenic co-substrate such as ethanol. This could indicate that biological DIET occurs and competes with hydrogen and formate during methanogenesis. Moreover, the addition of conductive microparticles, such as stainless steel and granular activated carbon, was found to increase methanogenic activity in disintegrated granules by 190 ± 18% and 175 ± 22% respectively as compared to disintegrated granules devoid of microparticles. The addition of non-conductive microparticles such as porcelain however decreased methanogenic activity by 65 ± 3% of the disrupted granules without microparticle activity. These results indicate that syntrophic bacteria from anaerobic sludge excluding Geobacter species can also carry out conductive mineral mediated DIET.

This study compares microbial and bioelectrochemical methods of biogas upgrade via CO2 conversion to CH4. First, an in situ approach for CO2 conversion is investigated in an anaerobic reactor with a continuous supply of exogenous H2. This approach increased CH4 content of the biogas to 80–85%, yet also increased the effluent acetate concentration to 5,000–6,000 mg L−1 due to homoacetogenic activity. In a second approach, an anaerobic biofilter was continuously fed with biogas and an exogenous supply of H2, resulting in a CH4 content of 85–90% and a H2 consumption of 4.2–4.5 mol per mol of CO2 removed. Finally, biogas upgrade via CO2 to CH4 conversion was demonstrated in the cathode compartment of a membraneless microbial electrosynthesis cell. This test resulted in a CH4 purity of 85 – 90% and an energy consumption (per L of treated biogas) of 3.1 ± 1.6 Wh L−1.

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.

Distinctions in hydrolysis and acidogenesis were examined for a series of anaerobic batch reactors inoculated with three different anaerobic mixed cultures (mesophilic, thermophilic and hyperthermophilic anaerobic sludge) and operated at the temperature of inoculum’s origin and additionally at 70 °C. Hyperthermophilic temperatures led to increased hydrolysis rates during the start-up stage but a rapid drop in pH limited the overall hydrolysis efficiency, indicating the importance of pH control to sustain the high reaction rates at higher temperatures. No significant difference (P > 0.05) was observed among hydrolysis efficiencies obtained for different reactors which ranged between 27 ± 3% and 40 ± 14%. The highest fermentation yield of 0.44 g COD of fermentation products/g VSS-CODadded was obtained under thermophilic conditions, followed by mesophilic (0.33 g COD ferm. prod./g VSS-CODadded) and hyperthermophilic conditions (0.05–0.08 g COD ferm. prod./g VSS-CODadded). Fermentative performance was better at mesophilic and thermophilic conditions as indicated by improved production of volatile fatty acids (VFA). VFAs accounted for 60–71% of the solubilised matter at thermophilic and mesophilic conditions. Acetic acid formed the primary VFA (70%) at mesophilic temperatures, while butyric acid was the major VFA at thermophilic (60%) conditions. Hyperthermophilic conditions led to increased production of lactic acid, which comprised up to 32% of the solubilised matter. Overall, the results indicate that different operating temperatures may not significantly affect the substrate degradation efficiency but clearly influence the biotransformation pathways.

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.

As an alternative to applying the hydrothermal treatment to the raw algal feedstock before the anaerobic digestion (i.e. pre-treatment), one considered a post-treatment scenario where anaerobic digestion is directly used as the primary treatment while the hydrothermal treatment is thereafter applied to the digestate. Hydrothermal treatments such as wet oxidation (WetOx) and hydrothermal carbonization (HTC) were compared at a temperature of 200 °C, for initial pressure of 0.1 and 0.82 MPa, and no holding time after the process had reached the temperature setpoint. Both WetOx and HTC resulted in a substantial solids conversion (47–62% with HTC, 64–83% with WetOx, both at 0.82 MPa) into soluble products, while some total chemical oxygen demand–based carbon loss from the solid-liquid phases was observed (20–39%). This generated high soluble products concentrations (from 6.2 to 10.9 g soluble chemical oxygen demand/L). Biomethane potential tests showed that these hydrothermal treatments allowed for a 4-fold improvement of the digestate anaerobic biodegradability. The hydrothermal treatments increased the methane yield to about 200 L STP CH 4 /kg volatile solids, when related to the untreated digestate, compared to 66 L STP CH 4 /kg volatile solids, without treatment.

This paper presents the raw data of biogas production and composition (relative pressures and concentrations of each of the biogas constituents) for batch experiments to evaluate the anaerobic digestion of xylose. Also, metagenomic sequencing data and analysis were reported. All data is available at Mendeley Data. 16S DNA sequencing data and metadata is available at MG-RAST (metagenomics.anl.gov/linkin.cgi?project = 9961). For further discussion, please refer to the scientific article entitled ''Effect of acidic and thermal pretreatments on a microbial inoculum for hydrogen and volatile fatty acids production through xylose anaerobic acidogenic metabolism'' (Mockaitis et al., 2020). Keywords: Dark fermentation, Hydrogen, Anaerobic digestion, Biogas, Xylose

BACKGROUND Anaerobic digestion of agricultural wastes is a cost effective way for combining resource recovery and methane production. This paper evaluates the co-digestion of cow manure and switchgrass in a completely stirred tank reactor (CSTR) by the electrolysis-enhanced anaerobic digestion (eAD) process. RESULTS The electrodes for water electrolysis were installed directly in an anaerobic digester and were used to create micro-aerobic conditions. Significant gains in process performance and biogas quality were obtained at current densities of 20–25 mA (per digester volume) with a corresponding volumetric energy consumption of 0.07–0.08 Wh . In particular, the COD removal rate was increased from 0.6 to 0.9 g COD d-1, methane production increased by 26%, and H2S content in the biogas declined from 2500–3000 ppm to less than 10 ppm. CONCLUSIONS The improved performance was achieved due to methane production from hydrolytic H2 and possibly due to the enhanced hydrolysis of organic matter. © 2013 Her Majesty the Queen in Right of Canada Journal of Chemical Technology & Biotechnology © 2013 Society of Chemical Industry

Methane production from the microalga Scenedesmus sp. AMDD digested in a continuously operated anaerobic reactor was studied under a range of conditions. Preliminary anaerobic toxicity assays revealed that methane yields and glucose consumption were inhibited by algae/sludge ratios in excess of 0.1 (g/g). Continuous digestions of microalgae at two hydraulic retention times (16 and 58 days) and two influent concentrations of algal feed (11 and 20 gTVS L− 1) were evaluated. Based on the amount of degraded algal biomass, a methane yield of 0.4 LCH4 gTVS‐ 1 was estimated. However, at a hydraulic retention time of 16 days only 52–53% of the algal biomass was degraded, primarily due to the limited hydrolysis of the algal cellular material. An increase of retention time to 58 days did not improve the degradation efficiency. Anaerobic decomposition of microalgae biomass appeared to affect composition of the microbial consortium in the digester, promoting the growth of sulfate-reducing bacteria leading to high levels of H2S in the biogas.

BACKGROUND: Electricity production in single-anode/cathode MFCs fed with simulated synthesis gas (syngas) as the sole electrondonorhasrecentlybeendemonstrated.Thisstudyevaluatedtheabilityofamulti-anode/cathodeMFCfedwithsyngas to achieve improved volumetric efficiency at several operating temperatures and electrode arrangements. RESULTS: A maximumpowerdensityof33mWL −1 R (normalizedtotheanodiccompartmentvolume)andacoulombicefficiency (CE) of 43% was achieved at an operating temperature of 37 ◦ C. MFC operation at 50 ◦ C resulted in a much lower power density of 10 mW L −1 R and a CE of 15%. The MFC power density was greatly impacted by the electrode arrangement and the highest power density was achieved in a three anode‐two cathode (3A-2C) arrangement. CONCLUSION: The multi-electrode design enhanced the performance of a syngas-fed MFC, which could have major economic and operational implications for designing large-scale syngas-fed MFCs. The MFC performance at elevated temperatures was restricted by low microbial activity, implying that a thermophilic rather than a mesophilic inoculum might be required for successful operation under thermophilic conditions. c � 2013 Society of Chemical Industry

Electrochemical impedance spectroscopy, cyclic voltammetry, and polarization tests were used to monitor the progress of the anode colonization by electrode-reducing microorganisms in a single-chamber membraneless microbial fuel cell seeded with anaerobic sludge. The electrochemical methods showed that an increase in microbial fuel cell power output coincided with a progressive decrease of the anode internal resistance and a more negative open circuit potential. Two redox systems were observed in cyclic voltammograms shortly after microbial fuel cell startup, while a redox system with a peak around −330 mV (vs. Ag/AgCl) was predominant in the mature biofilm. The redox systems were also dependent on the external resistance chosen for microbial fuel cell operation. This suggests that within the diverse microbial populations several species are capable of electron transfer to the anode, and that the microorganisms with the highest electron transfer rate become predominant. Furthermore, the growth of these electrode-reducing microorganisms can be accelerated by optimizing the microbial fuel cell electrical load.

Hydrogen conversion of CO by a pure culture of Carboxydothermus hydrogenoformans was investigated and optimized in a lab-scale hollow fiber membrane bioreactor (HFMBR). The reactor was operated under strict anaerobic, extremely thermophilic (70 °C) conditions with a continuous supply of gas, for four months. Reactor performance was evaluated under various operational conditions, such as liquid velocity (vliq) (13, 65 and 130 m h−1), temperature (70, 65, and 60 °C), CO pressure (from 1 to 2.5 atm) and CO loading rate (from 1.3 to 16 . 5 mol L rxr − 1 d − 1 ). Overall, results indicated a relatively constant H2 yield of 92 ± 4% (mol mol−1) regardless of the operational condition tested. Permeation across the colonized membrane was improved by three orders of magnitude as compared to the abiotic membrane, because of dissolved CO concentration was constantly maintained low in the liquid on the shell side of the membrane as continually depleted by the microorganisms. Once the biofilm was sufficiently developed, a maximum CO conversion activity of 0.44 mol CO g−1 volatile suspended solid (VSS) d−1 was achieved at a pCO of 2 atm or above and a vliq of 65 m h−1. However, this highest activity represented only 15% of the maximal activity potential of the strain under non-limiting conditions, attributed to the low concentration of dissolved CO (0.01–0.07 mM) present in the HFMBR liquid. Higher vliq (130 m h−1) produced shearing stress, which detached a significant portion of the biofilm from the membrane, and/or prevented less sessile growth (57% total biomass as biofilm, as opposed to 84–86% at lower vliq). One may deduce from this work that the volumetric CO conversion performance of such a membrane bioreactor would be at the most in the range of 5 mol CO L rxr − 1 d − 1 . Overall, the CO conversion performance in the HFMBR was biokinetically limited, when not limited by gas–liquid mass transfer. Additionally, over time, membrane fouling and aging decreased membrane permeability such that the CO transfer rate would be the most limiting factor in the long run.

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.

In-storage psychrophilic anaerobic digestion develops by microbial acclimation in covered swine-manure storage tanks, producing CH4 and stabilizing organic matter. To optimize the system's performance, the process kinetics must be understood. The objective of this study was to evaluate kinetic parameters describing the major stages in the digestion process, and to investigate the effect of temperature acclimation on these parameters. Specific activity tests were performed using manure inocula and five substrates at three incubation temperatures. Extant substrate activities were determined analytically for each case, and intrinsic kinetic parameters for glucose uptake were estimated by grid search fitting to the Monod model. The results demonstrate that this acclimated microbial community exhibits different kinetic parameters to those of the mesophilic communities currently modelled in the literature, with increased activity at low temperatures, varying with substrate and temperature. For glucose, the higher uptake is accompanied by lower microbial yield and half-saturation constant. Decomposing these values suggests that active psychrophilic and mesophilic microbial populations co-exist within the community. This work also confirms that a new method of assessing microbial substrate kinetics must be developed for manure microbial communities, separating microbial mass from other suspended organics.

The conversion of cellulosic crops into biofuels, including methane, is receiving a lot of attention lately. Panicum vergatum , or switchgrass, is a warm season perennial grass well adapted to grow in North America. Different pre-treatments were tested in 0.5 l batch reactors, at 35 °C, in order to enhance the methane production from switchgrass, including temperature, sonication, alkalinization and autoclaving. The methane production on the basis of volatile solids (VS) added to the fermentation were 112.4 ± 8.4, 132.5 ± 9.7 and 139.8 ml g −1 after 38 days of incubation for winter harvested switchgrass (WHS) after grinding, grinding with alkalinization, and grinding with alkalinization and autoclaving, respectively. The methane production was higher for fresh summer harvested switchgrass (SHS), with a production of 256.6 ± 8.2 ml g −1 VS after mulching, alkalinization and autoclaving. The methane production from SHS was improved by 29 and 42% when applying lignin (LiP) or manganese peroxidase (MnP), at 202.1 ± 9.8 and 222.9 ± 22.5 ml g −1 VS, respectively. The combination of an alkali pre-treatment with the MnP increased the methane production furthermore at 297.7 ml g −1 VS. The use of pectinases without chemical pre-treatment showed promising yields at 287.4 and 239.5 ml g −1 VS for pectate-lyase and poly-galacturonase, respectively. An estimation of the methane yield per hectare of crop harvested resulted in net energy production of 29.8, 49.7 and 78.1 GJ for winter harvested switchgrass, mulched and pretreated summer harvested switchgrass, respectively. Switchgrass represents an interesting candidate as a lignocellulosic crop for methane production.

This study describes a novel method for controlling applied voltage in a microbial electrolysis cell (MEC). It is demonstrated that the rate of hydrogen production could be maximized without excessive energy consumption by minimizing the apparent resistance of the MEC. A perturbation and observation algorithm is used to track the minimal apparent resistance by adjusting the applied voltage. The algorithm was tested in laboratory-scale MECs fed with acetate or synthetic wastewater. In all tests, changes in MEC performance caused by the variations in organic load, carbon source properties, and hydraulic retention time were successfully followed by the minimal resistance tracking algorithm resulting in maximum hydrogen production, while avoiding excessive power consumption. The proposed method of real-time applied voltage optimization might be instrumental in developing industrial scale MEC-based technologies for treating wastewaters with varying composition.

Covering a concrete manure storage tank with an air-tight floating membrane should induce anaerobic digestion of the stored manure. If the microbial community in the manure can acclimate to the ambient conditions, then In-Storage Psychrophilic Anaerobic Digestion (ISPAD) could be used by Canadian livestock producers to produce methane and stabilize manure. The objective of this study was to determine whether the microbial community in swine manure can successfully acclimate to the psychrophilic operating conditions in ISPAD and develop robust anaerobic digestion. This was done in the laboratory by analyzing manure from a three-year old full-scale pilot ISPAD facility located in St. Francois Xavier, Quebec, Canada, along with fresh manure and manure from an uncovered storage tank. Biochemical methane production assays performed at the three temperatures were used to quantify the performance of the microbial community and its temperature dependence. The ISPAD microbial community produced methane, in terms of VS added, at rates of 44.6, 9.8 and 8.5 dm 3 kg −1 d −1 , at 35, 18 and 8 °C, respectively. The ISPAD process reduced the organic matter content of the manure by 24% while releasing 63% of the potential methane in the manure, as opposed to the open storage tank where no measurable reduction in solids occurred, and only 15% of the potential methane was released. These results indicate that a robust, acclimated microbial community actively digests manure in the pilot ISPAD installation.

This study demonstrates enhanced methane production from wastewater in laboratory-scale anaerobic reactors equipped with electrodes for water electrolysis. The electrodes were installed in the reactor sludge bed and a voltage of 2.8–3.5 V was applied resulting in a continuous supply of oxygen and hydrogen. The oxygen created micro-aerobic conditions, which facilitated hydrolysis of synthetic wastewater and reduced the release of hydrogen sulfide to the biogas. A portion of the hydrogen produced electrolytically escaped to the biogas improving its combustion properties, while another part was converted to methane by hydrogenotrophic methanogens, increasing the net methane production. The presence of oxygen in the biogas was minimized by limiting the applied voltage. At a volumetric energy consumption of 0.2–0.3 Wh/L R , successful treatment of both low and high strength synthetic wastewaters was demonstrated. Methane production was increased by 10–25% and reactor stability was improved in comparison to a conventional anaerobic reactor.

Electricity generation in microbial fuel cells (MFCs) has been a subject of significant research efforts. MFCs employ the ability of electricigenic bacteria to oxidize organic substrates using an electrode as an electron acceptor. While MFC application for electricity production from a variety of organic sources has been demonstrated, very little research on electricity production from carbon monoxide and synthesis gas (syngas) in an MFC has been reported. Although most of the syngas today is produced from non-renewable sources, syngas production from renewable biomass or poorly degradable organic matter makes energy generation from syngas a sustainable process, which combines energy production with the reprocessing of solid wastes. An MFC-based process of syngas conversion to electricity might offer a number of advantages such as high Coulombic efficiency and biocatalytic activity in the presence of carbon monoxide and sulfur components. This paper presents a discussion on microorganisms and reactor designs that can be used for operating an MFC on syngas.

This study investigated the effects of microwave pretreatment of switchgrass in order to enhance its anaerobic digestibility. Response surface analysis was applied to screen the effects of temperature and time of microwave pretreatment on matter solubilisation. The composite design showed that only temperature had a significant effect on solubilisation level. Then the effects of the microwave pretreatment were correlated to the pretreatment temperature. The sCOD/tCOD ratio was equal to 9.4% at 90 °C and increased until 13.8% at 180 °C. The BMP assays of 42 days showed that microwave pretreatment induced no change on the ultimate volume of methane but had an interesting effect on the reaction kinetic. Indeed, the time required to reach 80% of ultimate volume CH4 is reduced by 4.5 days at 150 °C using the microwave pretreatment.

This work evaluates the impact of the external resistance (electrical load) on the long-term performance of a microbial fuel cell (MFC) and demonstrates the real-time optimization of the external resistance. For this purpose, acetate-fed MFCs were operated at external resistances, which were above, below, or equal to the internal resistance of a corresponding MFC. A perturbation/observation algorithm was used for the real-time optimal selection of the external resistance. MFC operation at the optimal external resistance resulted in increased power output, improved Coulombic efficiency, and low methane production. Furthermore, the efficiency of the perturbation/observation algorithm for maximizing long-term MFC performance was confirmed by operating an MFC fed with synthetic wastewater for over 40 days. In this test an average Coulombic efficiency of 29% was achieved.

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A single liquid chamber microbial fuel cell (MFC) with a gas-collection compartment was continuously operated under electrically assisted conditions for hydrogen production. Graphite felt was used for anode construction, while the cathode was made of Pd/Pt coated Toray carbon fiber paper with a catalyst loading of 0.5 mg cm −2 . To achieve hydrogen production, the MFC was connected to a power supply and operated at voltages in a range of 0.5–1.3 V. Either acetate or glucose was used as a source of carbon. At an acetate load of 1.67 g (L A d) −1 , the volumetric rate of hydrogen production reached 0.98 L STP (L A d) −1 when a voltage of 1.16 V was applied. This corresponded to a hydrogen yield of 2 mol (mol-acetate) −1 with a 50% conversion efficiency. Throughout the experiment, MFC efficiency was adversely affected by the metabolic activity of methanogenic microorganisms, which competed with exoelectrogenic microorganisms for the carbon source and consumed part of the hydrogen produced at the cathode.

In this study, an ADM1-based distributed parameter model was validated using experimental results obtained in a laboratory-scale 10 L UASB reactor. Sensitivity analysis of the model parameters was used to select four parameters for estimation by a numerical procedure while other parameters were accepted from ADM1 benchmark simulations. The parameter estimation procedure used measurements of liquid phase components obtained at different sampling points in the reactor and under different operating conditions. Model verification used real time fluorescence-based measurements of chemical oxygen demand and volatile fatty acids at four sampling locations in the reactor. Overall, the distributed parameter model was able to describe the distribution of liquid phase components in the reactor and adequately simulated the effect of external recirculation on degradation efficiency. The model can be used in the design, analysis and optimization of UASB reactors.

The transport of gellan gum microbeads as potential cell carriers was investigated in horizontal columns packed with different grain size classes of gravel (2–16 mm) and sand (0.25–2 mm). A suspension of microbeads was pulsed into each column for 6 h, followed by injection of water for 42 h. In general, the total amount of microbeads travelling across a given section of the column increased with injection time but decreased towards the column outlet, varying as a direct function of grain size. The results of this study demonstrate the feasibility of the transport of gellan gum microbeads through medium sand to medium gravel across distances up to 110 cm. On a etudie le transport de microbilles de gomme comme supports potentiels de cellules, dans des colonnes horizontales garnies de gravier et de sable de differentes classes de tailles de grains (2-16 mm) et de (0,25-2 mm). Une solution de microbilles est injectee dans chaque colonne pendant 6 h, suivie d'une injection d'eau pendant 42 h. En general, la quantite totale de microbilles se deplacant dans une section donnee de la colonne augmente avec le temps d'injection mais diminue vers la sortie de la colonne, variant en fonction directe de la taille des grains. Les resultats de cette etude montrent la faisabilite du transport des microbilles de gomme gellane dans du gravier a grain moyen jusqu' au sable a grain moyen sur des distances atteignant 110 cm.

env, The 11th World Congress on Anaerobic Digestion (AD11), 23-27 September 2007, Brisbane, Australia

Mycobacterium austroafricanum IFP 2012 is able to slowly grow on methyl tert-butyl ether (MTBE), a fuel oxygenate widely used as a gasoline additive. The potential of M. austroafricanum IFP 2012 for aerobic MTBE degradation was investigated in the presence of a secondary carbon source, isopropanol. The strain was then tested for MTBE biodegradation at the laboratory-scale in a fixed-bed reactor using perlite as the matrix, and isopropanol was injected once a week to maintain M. austroafricanum IFP 2012 biomass inside the perlite bed. The biofilter was operated for 85 days at an influent flow rate of 20 ml/h by varying the MTBE concentration from 10 to 20 mg/l. The hydraulic retention time was fixed at 5 days. The removal of MTBE depended on the inlet MTBE concentration and a MTBE removal efficiency higher than 99% was obtained for MTBE concentrations up to 15 mg/l. A set of 16S rRNA gene primers specific for M. austroafricanum species was used to analyze the DNA extracted from the biofilter effluent in order to detect the presence of M. austroafricanum IFP 2012 and to estimate the effect of periodic injections of isopropanol on the release of the strain from the perlite bed. The results demonstrated that the injection of isopropanol served to maintain an active MTBE degrading biomass in the biofilter and that this system could be used to effectively treat MTBE contaminated groundwater.

The electrolytical methanogenic/methanotrophic coupling (eMaMoC) process was tested in a laboratory-scale single-stage reactor for the treatment of tetrachloroethene (PCE)-contaminated waters. A water electrolysis cell was placed directly in the effluent recirculation loop for the supply of both O2 and H2 to the system: H2 serving as the electron donor for both carbonate reduction into CH4 and reductive dechlorination. The concurrent presence of O2 and CH4 could be used by the methanotrophs for co-metabolically oxidising the chlorinated intermediates left over by the anaerobic transformation of PCE. At a PCE inlet of 33–52 μM and a hydraulic residence time (HRT) of 5.6 days, PCE reductive dechlorination to dichloroethene (DCE) was over 95% with a maximum DCE mineralisation of 83%. Fluorescence in situ hybridisation with 16S rRNA probes related to type I and type II methanotrophic bacteria were utilised to localise the methanotrophic communities in the anaerobic/aerobic granules. It evidenced that with operational time, along with increasing oxygenation rate, methanotrophic communities were specifically colonising onto the outermost layer of the anaerobic/aerobic granule.

In this study, temperature variations in a mesophilic anaerobic reactor were used to control the reactor degradation capacity. When the reactor temperature was periodically changed from 32°C to 46°C with a period of 12 h, a near liner increase in methane production in response to temperature augmentation was observed. Furthermore, when the reactor temperature was increased during increased organic load, it resulted in a lower effluent concentration of volatile fatty acids and an increased chemical oxygen demand (COD) removal rate. A feedback control algorithm, which was based on a multi-model observer-based estimator of the anaerobic digestion process, was developed. The algorithm increased reactor temperature in response to increasing effluent COD concentration. It was successfully tested in a 10 L laboratory-scale reactor.

Direct interspecies electrons transfer (DIET) is a syntrophic metabolism in which free electrons flow from one cell to another without being shuttled by reduced molecules such as molecular hydrogen or formate. As more and more microorganisms show a capacity for electron exchange, either to export or import them, it becomes obvious that DIET is a syntrophic metabolism that is much more present in nature than previously thought. This article reviews literature related to DIET, specifically in reference to anaerobic digestion. Anaerobic granular sludge, a biofilm, is a specialized microenvironment where syntrophic bacterial and archaeal organisms grow together in close proximity. Exoelectrogenic bacteria degrading organic substrates or intermediates need an electron sink and electrotrophic methanogens represent perfect partners to assimilate those electrons and produce methane. The granule extracellular polymeric substances by making the biofilm matrix more conductive, play a role as electrons carrier in DIET.

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.

Direct interspecies electrons transfer (DIET) is a syntrophic metabolism in which free electrons flow from one cell to another without being shuttled by reduced molecules such as molecular hydrogen or formate. As more and more microorganisms show a capacity for electron exchange, either to export or import them, it becomes obvious that DIET is a syntrophic metabolism that is much more present in nature than previously thought. This article reviews literature related to DIET, specifically in reference to anaerobic digestion. Anaerobic granular sludge, a biofilm, is a specialized microenvironment where syntrophic bacterial and archaeal organisms grow together in close proximity. Exoelectrogenic bacteria degrading organic substrates or intermediates need an electron sink and electrotrophic methanogens represent perfect partners to assimilate those electrons and produce methane. The granule extracellular polymeric substances by making the biofilm matrix more conductive, play a role as electrons carrier in DIET., Series: Advances in Biochemical Engineering/Biotechnology; no. 151

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.

A multi-model observer based estimator (OBE), which consists of a set of simple sub-models describing typical process states and a knowledge-based system, was developed for monitoring and long-term prediction of the anaerobic digestion process. The knowledge-based system uses biogas and pH measurements for process diagnosis, while OBE uses fluorescence-based measurements of chemical oxygen demand (COD) and volatile fatty acids (VFAs) for estimating process outputs. The approach was tested on experimental results obtained from the operation of a lab-scale anaerobic reactor. The sub-models used either Monod or a combination of zero- and first-order rate expressions. A comparison showed that while both multi-model OBEs featured rapid convergence and good stability, the combined zero- and first-order kinetic equations provided better long-term prediction accuracy.

In this work, rhodamine-related fluorescence was measured on-line at four reactor heights in order to study hydrodynamics within an upflow anaerobic sludge bed reactor. A linear dependence of the dispersion coefficient (D) on the upflow velocity was observed, while the influence of the organic loading rate (OLR) was insignificant. Furthermore, the Bodenstein number of the reactor loaded with granulated sludge was found to be position-dependent with the largest values measured at the bottom of the sludge bed. This trend was not observed in the reactor without sludge. Chemical oxygen demand (COD) and volatile fatty acid (VFA) concentrations were measured at the same reactor heights as in rhodamine tests using conventional off-line analytical methods and on-line multiwavelength fluorometry. Significant spatial COD and VFA gradients were observed at organic loading rates above Click to view the MathML source and linear upflow velocities below 0.8 m h-1.

The removal of pyrene and benzo(a)pyrene from contaminated water by sequential and simultaneous ozonation-bioremediation techniques was investigated. During the sequential treatment, ozonation using 0.5 or 2.5 mg/L ozone was used as a pretreatment process, whereas, during the simultaneous treatment process, ozonation of hydrocarbon-contaminated water at a predetermined duration using 0.5 mg/L ozone was made in the presence of microbial biomass. Ozonation was not beneficial for the removal of pyrene. However, despite a decreased specific biodegradation rate, ozonation improved the overall elimination of benzo(a)pyrene during both treatment processes. The overall removal of benzo(a)pyrene increased from 23 to 91% after exposure of the water to 0.5 mg/L ozone for 30 minutes during the simultaneous treatment process and further to 100% following exposure to 2.5 mg/L ozone for 60 minutes during the sequential treatment mode, demonstrating the benefits of combined ozonation-biological treatment for the removal of polycyclic aromatic hydrocarbons.

The biotransformation and mineralization of a mixture of two polycyclic aromatic hydrocarbons (PAHs), anthracene and pyrene, which are known contaminants of soil and groundwater, by an enrichment culture in the presence or absence of 100 mg l(-1) Tergitol NP-10, a non-ionic surfactant, and at temperatures of 10 degrees C and 25 degrees C were investigated. The overall biotransformation of 2 mg l(-1) total PAHs with free cell suspensions in batch culture was greater than 97.2% at both examined temperatures. At 25 degrees C, the overall mineralization of anthracene was 48.8% and that of pyrene was 66.1%. However, the decrease of temperature to 10 degrees C had a negative effect on the mineralization of PAHs and reduced it to 18.5% and 61.5% for anthracene and pyrene, respectively. Using a higher PAHs concentration of 20 mg l(-1) at 25 degrees C, the overall biotransformation of anthracene was 80.7% and that of pyrene was 100%, where only 17.3% anthracene and 7.6% pyrene were mineralized to carbon dioxide and water. The addition of surfactant at 25 degrees C increased the overall mineralization of anthracene and pyrene to 33.0% and 27.6%, respectively. However, the addition of surfactant at 10 degrees C had a negative impact on the overall biotransformation of anthracene and pyrene, reducing them to 20.6% and 14.0%, respectively. These results have significant implications in the bioremediation of PAHs-contaminated sites.

This work studied trichloroethylene (TCE) degradation in a single stage coupled anaerobic–aerobic granular biofilm reactor. The co-existence of aerobic methanotrophic and anaerobic methanogenic bacteria in this reactor was expected to allow for a combination of reductive and oxidative pathways of TCE degradation and result in mineralization of TCE. First, the anaerobic–aerobic coupling was simulated using a mathematical model. Simulations of TCE degradation under different operating conditions suggested the superiority of the coupled reactor system over either aerobic or anaerobic process alone. Next, the approach of combining aerobic–anaerobic TCE degradation was validated in a reactor experiment. The experiment confirmed degradation of TCE due to the co-existence of methanogenic and methanotrophic populations in a single reactor.

Applicability of multi-wavelength fluorometry for anaerobic digestion process monitoring was investigated in a 3.5 L upflow anaerobic sludge bed (UASB) lab-scale reactor. Both off-line and on-line monitoring of key process parameters was tested. Off-line emission spectra were measured at an angle of 90° to the excitation beam using a cuvette. On-line measurements were carried out using a fiber optic probe in the external recirculation line of the digester. Fluorescence spectra were correlated to available analytical measurements to obtain partial least square regression models. An independent set of measurements was used to validate the regression models. Model estimations showed reasonable agreement with analytical measurements with multiple determination coefficients (R2) between 0.6 and 0.95. Results showed that off-line fluorescence measurements can be used for fast estimation of anaerobic digestor effluent quality. At the same time, the on-line implementation of multi-wavelength fluorescence measurements can be used for real-time process monitoring and, potentially, for on-line process control.

The Quebec Waste Management Policy (1998–2008) is requesting that the municipalities prepare a waste management plan, including a global objective of 60% of these wastes to be diverted from landfill sites by reduction, re-usage, recycling and valorization. Around 5.8 million tons of wastes were generated on the territory of the Montreal Metropolitan Community in 2001 for a population of about 3.5 millions citizens. In this paper, we present different management scenarios in which anaerobic digestion was used as a valorization step, focusing on the energetic value of the methane produced and the reduction in greenhouse gas (GHG) emissions. The four scenarios prepared cover the valorization of the organic fraction of municipal solid wastes, green wastes and excess sludge and showed potential methane generation of 17–140 Mm3 with a GHG reduction of 62,000–500,000 tons of CO2-equivalents.

This work examined the use of multi-wavelength fluorometry for on-line monitoring of an anaerobic digestion process. Experiments were carried out in a laboratory-scale anaerobic digestor fed with either synthetic or agricultural (cheese factory) wastewater. An in-line fiber optic probe installed in the external recirculation loop of the reactor was used to acquire fluorescence spectra with an interval of 5-10 min. The spectra were compared with analytical measurements taken at the same time to develop regression models, which were then used to predict concentrations of chemical oxygen demand, volatile fatty acids, and other key process parameters. A comparison of partial least squares (PLS), nonlinear principal components regression, and step-wise regression models on an independent set of data showed that the PLS model gave the best prediction accuracy.

A variable structure model (VSM) was used for on-line monitoring of an anaerobic digestor. The model consisted of three non-linear submodels representing typical states of the anaerobic digestion process and a knowledge-based system, which analyzed available process variables and handled submodel activation. At any instant, process dynamics was modeled only by one of the submodels, while others were considered trailing. The VSM was used to predict the experimental results obtained in a pilot scale anaerobic fixed-bed reactor.

In this work, trichloroethylene (TCE) degradation under combined anaerobic-aerobic conditions was studied in an ethanol-fed biofilm reactor oxygenated using hydrogen peroxide. The reactor was inoculated with a biomass originating from an anaerobic digestor. Granulated peat was added to the reactor as a substratum for biofilm development. Extensive characterization of reactor populations using activity tests and PCR analysis revealed the development of a mutualistic consortium, particularly methanotrophic and methanogenic microorganisms. This consortium was shown to degrade TCE by a combination of reductive and oxidative pathways. A near complete degradation of TCE at a load of 18 mg L(R)(-1) day(-1) was evidenced by a stoichiometric release of inorganic chloride.