Integration of acidogenic and methanogenic processes for simultaneous production of biohydrogen and methane from wastewater treatment

Feasibility of integrating acidogenic and methanogenic processes for simultaneous production of biohydrogen (H₂) and methane (CH₄) was studied in two separate biofilm reactors from wastewater treatment. Acidogenic bioreactor (acidogenic sequencing batch biofilm reactor, AcSBBR) was operated with designed synthetic wastewater [organic loading rate (OLR) 4.75 kg COD/m³-day] under acidophilic conditions (pH 6.0) using selectively enriched acidogenic mixed consortia. The resultant outlet from AcSBBR composed of fermentative soluble intermediates (with residual carbon source), was used as feed for subsequent methanogenic bioreactor (methanogenic/anaerobic sequencing batch biofilm reactor, AnSBBR, pH 7.0) to generate additional biogas (CH₄) utilizing residual organic composition employing anaerobic mixed consortia. During the stabilized phase of operation (after 60 days) AcSBBR showed H₂ production of 16.91 mmol/day in association with COD removal efficiency of 36.56% (SDR_A—1.736 kg COD/m³-day). AnSBBR showed additional COD removal efficiency of 54.44% (SDR_M—1.071 kg COD/m³-day) along with CH₄ generation. Integration of the acidogenic and methanogenic processes enhanced substrate degradation efficiency (SDR_T—4.01 kg COD/m³-day) along with generation of both H₂ and CH₄ indicating sustainability of the process.     

Harnessing of biohydrogen by acidogenic fermentation of Citrus limetta peelings: Effect of extraction procedure and pretreatment of biocatalyst

The extracts of Citrus limetta (sweet lime) peelings were evaluated as a fermentable substrate for hydrogen (H₂) production by dark-fermentation (acidogenic) using both anaerobic mixed consortia and selectively enriched acidogenic mixed consortia. Extraction was carried by pretreating sweet lime peelings at 121 °C (1 bar pressure) at variable pH (6 and 7) and digestion time (20 and 40 min). Maximum organic matter extraction was observed at pH 7.0 (40 min). Fermentation was performed at different organic loading conditions [OL1, 1.17 kg COD/m³; OL2, 2.35 kg COD/m³; OL3, 4.69 kg COD/m³] under acidophilic microenvironment. H₂ production was found to depend on the concentration of the substrate and composition. Increase in organic load showed consistent improvement in H₂ production. Operation at OL3 employing selectively enriched inoculum documented higher cumulative H₂ production (10.07 mmol) and H₂ production rate (0.345 mmol/h) (pH 7; 40 min). Substrate degradation was also found to increase with increase in organic loading. Maximum substrate degradation (SD) was registered at pH 6 (40 min) with anaerobic culture (2.80 kg COD_R/m³; ξ_COD 31.82%) and at pH 7 (40 min) with selectively enriched acidogenic culture (3.20 kg COD_R/m³; ξ_COD 36.36%). Concentration of volatile fatty acids (VFAs) also improved with increase in organic load. Maximum VFA concentration (1098 mg/l) was observed with OL3 (pH 7; 40 min) by using selectively enriched culture.     

Acidogenic hydrogen production from wastewater: Process analysis with the function of influencing parameters

Current communication reports the application of kinetic models viz., modified Gompertz, modified Logistic, Ratkowsky and Andrew model to study the acidogenic hydrogen (H₂) production along with volatile fatty acids (VFA) production and substrate degradation from various wastewater (dairy, distillery, chemical and designed synthetic wastewater) using mixed consortia. Influence of fermentation time was specifically evaluated by modified Gompertz and modified Logistic models on H₂ and VFA production. Influence of system redox condition on process was evaluated by Ratkowsky and Andrew models. The modified Gompertz model showed best fit for H₂ production as well as substrate degradation while modified Logistic model showed good acceptability with VFA production. The Andrew model describes both H₂ and VFA production with respect to system redox condition relatively well. This information provides an understanding of the process behavior, which can help in the design and upscaling of the process for efficient H₂ production. Copyright © 2015 John Wiley & Sons, Ltd.     

Utilizing acid-rich effluents of fermentative hydrogen production process as substrate for harnessing bioelectricity: An integrative approach

Lower substrate degradation is one of the limiting factors associated with fermentative hydrogen production process. To overcome this, an attempt was made to integrate microbial fuel cell (MFC) as a secondary energy generating process with the fermentative hydrogen (H₂) production. The acid-rich effluents generated from the acidogenic sequential batch biofilm reactor (AcSBBR) producing H₂ by fermenting vegetable waste was subsequently used as substrate for bioelectricity generation in single chambered MFC (air cathode; non-catalyzed electrodes). AcSBBR was operated at 70.4 kg COD/m³-day and the outlet was fed to the MFC at three variable organic loading rates. The final outlet from AcSBBR was composed of fermentative soluble acid intermediates along with residual carbon source. Experimental data illustrated the feasibility of utilizing acid-rich effluents by MFC for both additional energy generation and wastewater treatment. Higher power output (111.76 mW/m²) was observed at lower substrate loading condition. MFC also illustrated its function as wastewater treatment unit by removing COD (80%), volatile fatty acids (79%), carbohydrates (78%) and turbidity (65.38%) effectively. Fermented form of vegetable wastewater exhibited higher improvement (94%) in power compared to unfermented wastewater. The performance of MFC was characterized with respect to polarization behavior, cell potentials, cyclic voltammetry and sustainable power. This integration approach enhanced wastewater treatment efficiency (COD removal, 84.6%) along with additional energy generation demonstrating both environmental and economic sustainability of the process.     

Optimization and evaluation of fermentative hydrogen production and wastewater treatment processes using data enveloping analysis (DEA) and Taguchi design of experimental (DOE) methodology

The combined process efficiency with respect to fermentative hydrogen (H₂) production and wastewater treatment was evaluated in a series of batch experiments to enumerate the role of selected factors viz., origin of inoculum, pre-treatment, inlet pH and feed composition under anaerobic microenvironment using mixed culture. H₂ production and substrate degradation were found to depend significantly on the selected factors with individual conditions to achieve effective process performance. Significantly diverse operational conditions were observed for both H₂ production and substrate degradation with respect to process efficiency. However, while dealing with H₂ production in association with wastewater treatment, both the parameters are important and balancing the conditions for combined effective performance is critical. Data enveloping analysis (DEA) was applied to evaluate the combined system performance with respect to the two output parameters (H₂ production and substrate degradation) based on relative efficiency. Among various experimental combinations studied, those with untreated anaerobic mixed inoculum under acidophilic conditions (inlet pH 5.5) using simple wastewater as fermentative substrate illustrated combined process efficiency with respect to H₂ production (1.919 m mol H₂/day; 0.52 mol H₂/kg COD_R-day) and substrate degradation (substrate degradation rate, 4.56 kg COD/m³-day). DEA methodology provide the relative efficiency of the system by integrating two output parameters. Further, design of experimental methodology (DOE) by Taguchi approach was applied to enumerate the role of selected factors on the H₂ production and substrate degradation with the final aim of optimizing the process. By adapting the derived optimum conditions, the performance with respect to H₂ production and substrate degradation could be enhanced by three fold.     

Metabolic shift and electron discharge pattern of anaerobic consortia as a function of pretreatment method applied during fermentative hydrogen production

We have made an attempt to evaluate the variation in the electron discharge (ED) pattern of anaerobic consortia as a function of pretreatment viz., chemical, heat-shock, acid and oxygen-shock in comparison with untreated mixed consortia during fermentative hydrogen (H₂) production. Experiments were performed with dairy wastewater as substrate using anaerobic mixed consortia as biocatalyst (pretreated individually and in combination). Cyclic voltammetry (CV) elucidated significant variation in the ED pattern of mixed consortia along with H₂ production and substrate degradation (SD) as a function of pretreatment method applied. Higher ED was observed with all pretreated consortia which can be attributed to the stable proton (H⁺) shuttling due to the suppression of methanogenic activity. Oxygen-shock method and untreated consortia showed lower H₂ production and higher SD among the variations studied, while, combined pretreated consortia resulted higher H₂ production and lower SD. Lower ED observed with untreated consortia suggests the H⁺ reduction during methanogenesis rather than the inter-conversion of metabolites, which is presumed to be necessary for H₂ production. ED observed with combined pretreated consortia corroborated well with the observed H₂ production. Redox pairs were visualized on the voltammograms with almost all the experimental variations studied except untreated consortia. The potentials (E₀) of redox pairs observed were corresponding to intracellular electron carriers viz., NAD⁺/NADH (E₀ −0.32 V) and FAD⁺/FADH₂ (E₀ −0.24 V).     

Deoiled algal cake as feedstock for dark fermentative biohydrogen production: An integrated biorefinery approach

An integrated biorefinery approach utilizing deoiled algal cake (after lipid extraction) as potential feed-stock for biohydrogen (H₂) production using selectively enriched acidogenic consortia as biocatalyst was evaluated. Algae pretreated extract (AP-E) documented maximum H₂ production rate (HPR), cumulative H₂ production (CHP) and specific H₂ yield (SHY) with higher substrate degradation (65%) in terms of COD removal efficiency than other conditions, which is a good sign for waste remediation. Along with the biohydrogen production and substrate removal the consortia also produced good amount of volatile fatty acids (VFA). VFA production in fermentation media resulted in reactor pH drop. The study depicted the feasible use of deoiled algal biomass as feed-stock for H₂ production in the framework of biorefinery.     

Effluents with soluble metabolites generated from acidogenic and methanogenic processes as substrate for additional hydrogen production through photo-biological process

The feasibility of utilizing effluents generated from acidogenic [producing biohydrogen (H₂)] and methanogenic [producing methane] processes was studied for additional H₂ production by terminally integrating with photo-biological process employing enriched mixed culture. Experimental data has depicted enhanced process efficiency with respect to additional H₂ production and substrate degradation through photo-biological process. However, the efficiency was found to depend on the process used in the first stage along with nature and composition of the substrate. Acidogenic process in the first stage had more positive influence on photo-biological H₂ production [synthetic wastewater – 14.40 mol/Kg COD_R and 15.16 mol/Kg COD_R (with vitamins); dairy wastewater – 13.29 mol/Kg COD_R and 13.70 mol/Kg COD_R (with vitamins)] over the corresponding methanogenic process. Effluent generated from acidogenic treatment of dairy wastewater yielded high substrate degradation rate (SDR) [1.20 Kg COD/m³ day and 1.34 Kg COD/m³ day (vitamins)] followed by synthetic wastewater [0.92 Kg COD/m³ day and 1.05 Kg COD/m³ day (vitamins)]. Among the studied experimental variations chemical wastewater evidenced poor H₂ production and SDR. Vitamin solution showed positive influence on both H₂ production and wastewater treatment irrespective of the experimental variations studied.     

Bio-electrochemical evaluation of fermentative hydrogen production process with the function of feeding pH

Fermentative hydrogen (H₂) production process in concurrence with feeding pH [aciodophilic (pH 6.0) and neutral (pH 7.0)] and reactor operation mode (continuous and fed-batch) was evaluated in a biofilm configured reactor [upflow mode; retention time, 24 h; operating temperature, 28 ± 2 °C; organic loading rate, 3.4 kg COD/m³ day] using anaerobic mixed consortia. Acidophilic pH showed relatively effective performance with respect to H₂ production compared to neutral operation. Neutral pH illustrated effective substrate removal efficiency over the corresponding acidophilic operation. Fed-batch mode of operation with acidophilic pH showed highest H₂ production among the studied experimental variations. The pattern of soluble metabolites distribution showed the persistence of acid-forming metabolic flow associated with acidogenesis which may be considered as optimum microenvironment for effective H₂ production. Bio-electrochemical behavior of mixed anaerobic consortia (whole cell) during H₂ production process was evaluated employing cyclic voltammetry (CV) in electrochemical cell [platinum as working electrode; Ag/AgCl as reference electrode; graphite rod as counter electrode; wastewater as electrolyte] to gain insight into the possible mechanism based on intracellular electron transfer involved in the fermentative metabolic process. Voltammogram profiles visualized well defined redox pairs in forward and reverse scans at both pH conditions and the signals corresponded to intracellular electron carrier, NADH/NAD⁺ (E^0′, −0.32 V). Relatively higher energy output was observed in acidophilic operation which might be attributed to the possibility of efficient proton (H⁺) transfer between metabolic intermediates.     

Fermentative biohydrogen production by mixed anaerobic consortia: Impact of glucose to xylose ratio

Glucose and xylose are the dominant monomeric carbohydrates present in agricultural materials which can be used as potential building blocks for various biotechnological products including biofuels production. Hence, the imperative role of glucose to xylose ratio on fermentative biohydrogen production by mixed anaerobic consortia was investigated. Microbial catabolic H₂ and VFA production studies revealed that xylose is a preferred carbon source compared to glucose when used individually. A maximum of 1550 and 1650 ml of cumulative H₂ production was observed with supplementation of glucose and xylose at a concentration of 5.5 and 5.0 g L⁻¹, respectively. A triphasic pattern of H₂ production was observed only with studied xylose concentration range. pH impact data revealed effective H₂ production at pH 6.0 and 6.5 with xylose and glucose as carbon sources, respectively. Co-substrate related biohydrogen fermentation studies indicated that glucose to xylose ratio influence H₂ and as well as VFA production. An optimum cumulative H₂ production of 1900 ml for 5 g L⁻¹ substrate was noticed with fermentation medium supplemented with glucose to xylose ratio of 2:3 at pH 6. Overall, biohydrogen producing microbial consortia developed from buffalo dung could be more effective for H₂ production from lignocellulosic hydrolysates however; maintenance of glucose to xylose ratio, inoculum concentration and medium pH would be essential requirements.     

Behavior of acidogenesis during biohydrogen production with formate and glucose as carbon source: Substrate associated dehydrogenase expression

Experiments were designed to enumerate variation in biohydrogen (H₂) production pattern with formate and glucose as carbon source under acidogenic mixed microenvironment. High H₂ production was observed with glucose (180 ml) when compared to formate (152 ml). The process was validated with modified Gompertz model (R² = 0.98). Substrate degradation also showed higher removal of glucose (ξ_COD, 82%) compared to formate (ξ_COD, 53%). Nevertheless, specific H₂ yield of formate (6.6 mol H₂/kg COD_R) obtained was comparatively higher than glucose (5 mol H₂/kg COD_R). Variation in H₂ production was manifested by change in fatty acid composition and substrate degradation pattern. Acetate was obtained as a major metabolic intermediate from the degradation of glucose and a shift in the biochemical pathway towards formation of butyrate occurred after maximum substrate degradation. The role of substrate-dependent dehydrogenase activity was deciphered during H₂ production and was evidenced with bio-electrochemical analysis.     

Regulation of biohydrogen production by heat-shock pretreatment facilitates selective enrichment of Clostridium sp.

The effect of heat-shock treatment to selectively enrich acidogenic, H₂ producing consortia was investigated for inoculum preparation and to control the process operation. Long term operation (520 days) in suspended-batch mode bioreactors illustrated relative efficiency and feasibility of heat-shock treated consortia (15.78 mol/kg COD_R) in enhancing H₂ production (3.31 mol/kg COD_R) when compared to parent (control) consortia. On the contrary, substrate degradation was higher in the control operation (ξ_COD, 62.86%; substrate degradation rate (SDR), 1.34 kg COD_R/m³-day) compared to heat-shock operation (ξ_COD, 52.6%; SDR, 1.10 kg COD_R/m³-day). Heat-shock pretreatment has resulted in a marked fermentation pathway shift towards acetic-butyric acid type production. The microbial diversity illustrated dominance in the Clostridia class after applying heat-shock pretreatment. The redox catalytic currents and Tafel analysis strongly support the conclusion of an improved biocatalyst performance after pretreatment with regards to H₂ production.     

Acetate and butyrate as substrates for hydrogen production through photo-fermentation: Process optimization and combined performance evaluation

Organic acids viz., acetate and butyrate were evaluated as primary substrates for the production of biohydrogen (H₂) through photo-fermentation process using mixed culture at mesophilic temperature (34 °C). Experiments were performed by varying parameters like operating pH, presence/absence of initiator substrate (glucose) and vitamin solution, type of nitrogen source (mono sodium salt of glutamic acid and amino glutamic acid) and gas (nitrogen/argon) used to create anaerobic microenvironment. Experimental data showed the feasibility of H₂ production along with substrate degradation utilizing organic acids as metabolic substrate but was found to be dependent on the process parameters evaluated. Maximum specific H₂ production and substrate degradation were observed with acetic acid [3.51 mol/Kg COD_R-day; 1.22 Kg COD_R/m³-day (92.96%)] compared to butyric acid [3.33 mol/Kg COD_R-day; 1.19 Kg COD_R/m³-day (88%)]. Higher H₂ yield was observed under acidophilic microenvironment in the presence of glucose (co-substrate), mono sodium salt of glutamic acid (nitrogen source) and vitamins. Argon induced microenvironment was observed to be effective compared to nitrogen induced microenvironment. Combined process efficiency viz., H₂ production and substrate degradation was evaluated employing data enveloping analysis (DEA) methodology based on the relative efficiency. Integration of dark fermentation with photo-fermentation appears to be an economically viable route for sustainable biohydrogen production if wastewater is used as substrate.     

Biohydrogen production from purified terephthalic acid (PTA) processing wastewater by anaerobic fermentation using mixed microbial communities

Purified terephthalic acid (PTA) processing wastewater was evaluated as a fermentable substrate for hydrogen (H₂) production with simultaneous wastewater treatment by dark-fermentation process in a continuous stirred-tank reactor (CSTR) with selectively enriched acidogenic mixed consortia under continuous flow condition in this paper. The inoculated sludge used in the reactor was excess sludge taken from a second settling tank in a local wastewater treatment plant. Under the conditions of the inoculants not less than 6.3 gVSS/L, the organic loading rate (OLR) of 16 kgCOD/m³ d, hydraulic retention time (HRT) of 6 h and temperature of (35 ± 1) °C, when the pH value, alkalinity and oxidation–reduction potential (ORP) of the effluent ranged from 4.2 to 4.4, 280 to 350 mg CaCO₃/L, and −220 to −250 mV respectively, soluble metabolites were predominated by acetate and ethanol, with smaller quantities of propionate, butyrate and valerate. Stable ethanol-type fermentation was formed with the sum of ethanol and acetate concentration ratio of 70.31% to the total liquid products after 25 days operation. The H₂ volume content was estimated to be 48–53% of the total biogas and the biogas was free of methane throughout the study. The average biomass concentration was estimated to be 10.82 gVSS/L, which favored H₂ production efficiently. The rate of chemical oxygen demand (COD) removal reached at about 45% and a specific H₂ production rate achieved 0.073 L/gMLVSS d in the study. This CSTR system showed a promising high-efficient bioprocess for H₂ production from high-strength chemical wastewater.     

A rapid and simple protocol for evaluating biohydrogen production potential (BHP) of wastewater with simultaneous process optimization

Biohydrogen production utilizing negative valued waste through dark-fermentation process is one of the emerging areas. Reported conditions for H₂ production are significantly variable and comparative analysis of data is major problem for unified understanding. A simple, rapid and generalized two phase methodology/protocol was developed to evaluate the biohydrogen production potential (BHP) of negative valued wastewater as substrate/feed-stock for renewable biohydrogen production using mixed consortia. Critical factors that can influence the overall process viz., redox condition, organic load and biocatalyst were considered in the designing the methodology. Feasibility of protocol was initially evaluated with synthetic wastewater and further validated with real field composite food and slaughter house wastewaters. The selected operational factors showed marked influence on both H₂ production and wastewater treatment. The reported methodology/protocol not only provides the ability of selected wastewater to generate H₂ but also facilitates process understanding based on selected factors and finally acquiesce optimum conditions.     

Regulatory influence of CO2 supplementation on fermentative hydrogen production process

This study presents an approach to enhance fermentative biohydrogen (H₂) production by improving the system buffering capacity through utilization of CO₂ generated from syngas. The experimental data substantiates the positive impact of CO₂ sparging on H₂ production process. Various CO₂ sparging times viz., 30, 60 and 120 s were evaluated on H₂ production and substrate degradation. Based on the optimum sparging time (60 s), experiments were further performed to study the influence of pH microenvironment (5, 6 and 7) on the process efficiency. Further the influence of periodic CO₂ sparging was also evaluated. Experimental data visualized a marked improvement on the overall process performance based on H₂ production and substrate degradation after sparging CO₂. Carbonic acid upon association/dissociation forms bicarbonates in the system. Alkaline condition helps to build up buffering nature, which resist fluctuations in pH even at higher VFA concentrations. Substrate degradation was effective during intermittent sparging at neutral conditions. CO₂ sparging directly effecting the bulk liquid environment of the system improves buffering nature which indirectly helps to maintain favorable microenvironment for biohydrogen production process.     

Influence of reactor configuration on fermentative hydrogen production during wastewater treatment

Influence of reactor configuration [biofilm/suspended growth] on fermentative hydrogen (H₂) production and substrate degradation was evaluated employing anaerobic mixed consortia. Reactors were operated at acidophilic (pH 6.0) condition employing designed synthetic wastewater as substrate at an organic loading rate of 3.4 Kg COD/m³-day with a retention time of 24 h at 28 ± 2 °C. Experimental data enumerated the influence of reactor configuration on both H₂ production and wastewater treatment. Biofilm reactor (28.98 mmol H₂/day; 1.25 Kg COD/m³-day) showed relatively efficient performance over the corresponding suspended growth configuration (20.93 mmol H₂/day; 1.08 Kg COD/m³-day). Specific H₂ yields of 6.96 mmol H₂/g-COD_L-day (19.32 mmol H₂/g-COD_R-day) and 5.03 mmol H₂/g-COD_L-day (16.10 mmol H₂/g-COD_R-day) were observed during stabilized phase of operation of biofilm and suspended growth reactors respectively. Higher concentration of VFA generation was observed in the biofilm reactor. Both the configurations recorded higher acetate concentration over other soluble metabolites indicating the dominance of acid-forming metabolic pathway during the H₂ production process.     

The effect of hydraulic retention time on thermophilic dark fermentative biohydrogen production in the continuously operated packed bed bioreactor

The main objective of the study is to investigate the effect of hydraulic retention times on continuous dark fermentative biohydrogen production in an up-flow packed bed reactor (UPBR) containing a novel microorganism immobilization material namely polyester fiber beads. The hydrogen producing dark fermentative microorganisms were obtained by heat-pretreatment of anaerobic sludge from the acidogenic phase of an anaerobic wastewater treatment plant. Glucose was the sole carbon source and the initial concentration was 15 ± 1 g/L throughout the continuous feeding. UPBR was operated under the thermophilic condition at T = 48 ± 2 °C and at varying HRTs between 2 h and 6 h. The hydrogen productivity of continuously operated UPBR increased with increasing HRT. Hydrogen production volume varied between 4331 and 6624 ml/d, volumetric hydrogen production rates (VHPR) were obtained as 3.09–4.73 L H₂/L day, and hydrogen production yields (HY) were 0.49 mol/mol glucose-0.89 mol/mol glucose depending on HRT. Maximum daily hydrogen volume (6624 ml/d), the yield (0.89 mol/mol glucose) and VHPR (4.73 L H₂/L day) were obtained at HRT = 6 h. The production rate and the yield decreased with increasing organic loading rate due to substrate inhibition.     

Regulating biohydrogen production from wastewater by applying organic load-shock: Change in the microbial community structure and bio-electrochemical behavior over long-term operation

Detailed experiments were designed to evaluate the function of load-shock treatment strategy (50 g COD/l; 3 days) for selective enrichment of acidogenic hydrogen (H₂) producing consortia in comparison with untreated anaerobic consortia. Experiments performed in suspended-batch mode bioreactors for 520 days illustrated the relative efficiency of load-shock treated consortia in enhancing H₂ production (16.64 mol/kg COD_R) compared to untreated-parent consortia (3.31 mol/kg COD_R). On the contrary, substrate degradation was higher with control operation (ξ_COD, 62.86%; substrate degradation rate (SDR), 1.10 kg COD_R/m³-day) compared to load-shock culture (52.33%; 0.78 kg COD_R/m³-day). Fatty acid composition documented a shift in the metabolic pathway towards acetate formation after applying load-shock, which manifests higher H₂ production. Microbial profiling documented a significant alteration in species composition of microbial communities after repeated load-shock applications specific to enrichment of Firmicutes which are favourable for H₂ production. Dehydrogenase activity was stabilized with each re-treatment, signifying the adaptation inclination of the biocatalyst towards increased proton shuttling between metabolic intermediates, leading to higher H₂ production. Voltammograms of load-shock treated cultures showed a marked shift in oxidation and reduction catalytic currents towards more positive and negative values respectively with increasing scan rate evidencing simultaneous redox-conversion reactions, facilitating proton gradient in the cell towards increased H₂ production. Load-shock treatment facilitates direct cultivation of inoculums at higher substrate load without any chemical pretreatment. This study documented the feasibility of controlling microbial metabolic function by application of load-shock treatment either for preparing inoculum for startup of the reactor or to the reactor resident microflora (in situ) during operation whenever required to regain the process performance.     

Production of biohydrogen from brewery wastewater using Klebsiella pneumoniae isolated from the environment

The use of wastewater for the biological production of H₂ (biohydrogen) by dark fermentation has been studied for a variety of waste substrates and mixed or isolated inocula. However, for brewery wastewater (BW), which is generated in large volumes and has characteristics that are highly suitable for acidogenic fermentation, the available studies describe the use of mixed cultures, especially pretreated methanogenic inocula. The aim of this work was to isolate an enterobacterium from aviary litter that was capable of fermenting BW and generating biogas rich in H₂. The biochemical characterization and species confirmation confirmation revealed the isolation of Klebsiella peneumoniae, which provided efficient production of biogas rich in H₂ (30–40%) in batch assays performed for up to 72 h, with the inoculum in suspension, at a small scale (in serum bottles) and using a mechanically-stirred anaerobic reactor (AnBBR), employing crude BW without any supplementation. The hydrogen yield and molar hydrogen flow rate were 0.80–1.67 mol H₂ mol^?1 glucose and 0.2–2.2 mmol H₂ h^?1, respectively, indicating good performance of the inoculum in metabolizing this substrate and the possibility of optimizing the process by varying the duration of the batch.