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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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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