Fermentative H2 Research Articles

Effects of alginate immobilization on dynamic membrane formation and H2 fermentation from galactose

A dynamic membrane (DM) is a biofilm that forms on a support material, acting as a filter to retain high-density biomass. This study aims to explain the effects of alginate immobilization on DM formation during dark-H2 fermentation. Galactose is used as a model substrate. Heat-treated anaerobic sludge, with and without immobilization, is used for an inoculum for two identical lab-scale DM bioreactors (DMBR). The DMBRs are continuously operated for more than 40 days by changing the hydraulic retention time (HRT) from 12 to 3 h. Biomass retention and H2 production performance are significantly improved at an HRT of 3 h with immobilization. The alginate-added bioreactor shows higher extracellular polymeric substance content both in the mixed liquor and the DM. At an HRT of 3 h with immobilization, the fraction of Sporolactobacillus spp. and Lactobacillus spp. increases, possibly contributing to DM formation. However, lactic-acid concentration does not increase, implying it can be further consumed by the dominant bacteria, Clostridium butyricum.

Enhanced dark fermentative H2 production by agar-immobilized cyanobacterium Aphanothece halophytica

Cell immobilization is one of the techniques used to improve H2 productivity in cyanobacteria. In this study, H2 production by immobilized cells of unicellular halotolerant cyanobacterium Aphanothece halophytica was investigated and optimized. The results showed that immobilized cells of A. halophytica had higher H2 production than free cells under nitrogen-deprived condition. Among various support material types used, agar-immobilized cells showed the highest H2 production rate. Under nitrogen deprivation, the optimal conditions of cell immobilization for H2 production were 3% (w/v) agar concentration, 0.2 mg dry cell weight per mL of gel solution, and 0.125 cm3 of agar cube. The optimum pH of medium and incubation temperature for H2 production by agar-immobilized cells were pH 7.4 and 40 °C, respectively. Using a large glass vial and headspace volume resulted in enhancement of H2 production by agar-immobilized cells. Finally, H2 production by agar-immobilized cells was analyzed for three consecutive cycles. H2 production could be maintained at the highest level after two cycles when half of immobilized cells were replaced with fresh immobilized cells. These findings indicate that the enhanced H2 production of the unicellular halotolerant cyanobacterium A. halophytica can be achieved by immobilization method, thus providing the possibility to improve H2 production by cyanobacteria in the future.

Investigating how biomass hydrolysis derivatives inhibit H2 production by an isolated Clostridium beijerinckii

This study evaluates how fermentation inhibitors derived from biomass, namely 5-hydroxymethylfurfural (HMF), levulinic acid (LA), and formic acid (FA), affect H2 production by a Clostridium beijerinckii strain. The specific fermentative H2 production rate (μH2), bacterial cell growth rate (μ), and substrate (glucose) consumption rate (μS) during fermentation helped to estimate which HMF, LA, and FA concentrations inhibited 50% of the rates (IC50). IC50 for μ was 2.4, 2.7, and 1.4 g/L for HMF, LA, and FA, respectively. HMF inhibited H2 production the most potently and favored the lactate and ethanol pathways. Butyric acid was the only metabolite to be detected in the presence of LA or FA, which attested that these inhibitors completely inhibited the acetate pathway. The glucose consumption rate was the least affected by the inhibitors, and FA was more potent than HMF and LA. This information should be useful for more appropriate biomass feedstock application in fermentative H2 production.

Bioconversion of Chicken Feather Meal by Aspergillus niger: Simultaneous Enzymes Production Using a Cost-Effective Feedstock Under Solid State Fermentation.

This study reported for the first time the simultaneous production of hydrolytic enzymes by Aspergillus niger under solid state fermentation using chicken feather meal as substrate. The effect of some culture parameters for production of protease, lipase, phytase and keratinase enzymes was evaluated using a central composite rotatable design. The results obtained demonstrated that the independent variables initial moisture of the culture medium and incubation temperature presented as highly significant on the enzymes production. The production of protease and lipase followed a similar profile, in which the highest values of enzymatic activities were detected after 48h of fermentation. The conduction of the fermentative process using an initial moisture of 50%, 30°C as incubation temperature and supplementation of the feather meal with 15% wheat bran resulted in higher yields of protease (> 300Ug-1) and lipase (> 90Ug-1) after 48h and satisfactory values of phytase activity (> 70Ug-1) after 72h. No significant effects of the independent variables on keratinase production were observed. However, under the selected conditions for the other enzymes, keratinase production reached values higher than 13Ug-1 after 72h fermentation. Thus, our work contributed to the proposal of an alternative process for the simultaneous production of proteases, lipases, phytases and keratinases in a single and simplified process using chicken feather meal.

Impacts of short-term temperature fluctuations on biohydrogen production and resilience of thermophilic microbial communities

Anaerobic microflora enriched for dark fermentative H2 production from a mixture of glucose and xylose was used in batch cultivations to determine the effects of sudden short-term temperature fluctuations on H2 yield and microbial community composition. Batch cultures initially cultivated at 55 °C (control) were subjected to downward (from 55 °C to 35 °C or 45 °C) or upward (from 55 °C to 65 °C or 75 °C) temperature shifts for 48 h after which, each culture was transferred to a fresh medium and cultivated again at 55 °C for two consecutive batch cycles. The average H2 yield obtained during the first cultivation at 55 °C was 2.1 ± 0.14 mol H2 mol−1 hexose equivalent. During the temperature shifts, the obtained H2 yields were 1.8 ± 0.15, 1.6 ± 0.27 and 1.9 ± 0.00 mol H2 mol−1 hexose equivalent at 35 °C, 45 °C and 65 °C, respectively, while no metabolic activity was observed at 75 °C. The sugars were completely utilized during the 48 h temperature shift to 35 °C but not at 65 °C and 45 °C. At the end of the second cycle after the different temperature shifts, the H2 yield obtained was 96.5, 91.6, 79.9 and 54.1% (second cycle after temperature shift to 35 °C, 45 °C, 65 °C and 75 °C, respectively) when compared to the average H2 yield produced in the control at 55 °C. Characterization of the microbial communities present in the control culture at 55 °C showed the predominance of Thermoanaerobacteriales, Clostridiales and Bacilliales. The microbial community composition differed based on the fluctuation temperature with Thermoanaerobacteriales being most dominant during the upward temperature fluctuations and Clostridiales being the most dominant during the downward temperature fluctuations.

Production of a Potentially Synbiotic Pomegranate Beverage by Fermentation with Lactobacillus plantarum ATCC 14917 Adsorbed on a Prebiotic Carrier.

A probiotic biocatalyst was prepared through Lactobacillus plantarum ATCC 14917 immobilization on a prebiotic carrier (delignified wheat bran) and was used for fermentations of pomegranate juice. Initially, pomegranate juice was fermented for 24h and then was stored for 28days at 4°C. The obtained results regarding sugar and organic acid analysis revealed that the probiotic biocatalyst was effective. Ethanol was produced in small amounts (0.4-1% v/v). Total phenolic content and antioxidant activity was greater in the fermented pomegranate juice than in unfermented juice after 24h of fermentation and over the time span of 28days. Viability of probiotic cells was well maintained (above 8.65 log cfu/mL) after 24h of fermentation and during 4weeks of storage at 4°C, and it is noteworthy that no pathogens were observed. The strength of viability of probiotic cells can be attributed to the immobilization carrier (delignified wheat bran) that exhibits prebiotic properties providing a protective effect to the cells. Finally, the proposed bioprocess of employing the proposed synbiotic biocatalyst for pomegranate juice fermentation shows great potential for commercialization while sensory evaluation highlights the degree of quality of the produced functional pomegranate beverages.

In vitro fermentation of copra meal hydrolysate by human fecal microbiota.

Copra meal hydrolysate (CMH) is obtained by hydrolyzing defatted copra meal with β-mannanase from Bacillus circulans NT 6.7. In this study, we investigated the resistance of CMH to upper gastrointestinal tract digestion and the fecal fermentation profiles of CMH. Fecal slurries from four healthy human donors were used as inocula, and fructooligosaccharides (FOS) were used as a positive prebiotic control. Fecal batch cultures were performed at 37°C under anaerobic conditions. Samples were collected at 0, 10, 24 and 34h for bacterial enumeration via fluorescent in situ hybridization and organic acid (OA) analysis. In vitro gastric stomach and human pancreatic α-amylase simulations demonstrated that CMH was highly resistant to hydrolysis. Acetate was the main fermentation product of all the substrates. The proportions of acetate production of the total OAs from FOS, CMH and yeast mannooligosaccharides (MOS) after 34h of fermentation did not significantly differ (69.76, 65.24 and 53.93%, respectively). At 24h of fermentation, CMH promoted the growth of Lactobacillus and Bifidobacterium groups (P < 0.01) and did not significantly differ from the results obtained using FOS. The results of in vitro fecal fermentation of CMH indicate that CMH can promote the growth of beneficial bacteria.

Influence of phytase enzyme on ruminal biogas production and fermentative digestion towards reducing environmental contamination.

Environmental impact of livestock production has received a considerable public scrutiny because of the adverse effects of nutrient run-offs, primarily N and P, from agricultural land harboring intensive energy livestock operations. Hence, this study was designed to determine the efficacy of dietary phytase supplementation on fermentation of a sorghum grain-based total mixed ration (TMR) using a ruminal in vitro digestion approach. Phytase was supplemented at three doses: 0 (control), 540 (P540), and 720 (P720)g/t dry matter, equivalent to 0, 2.7 × 106, and 3.6 × 106 CFU/t DM, respectively. Compared to P720 and the control, gas production was higher for P540 after 12h (P= 0.02) and 24h (P= 0.03) of fermentation suggesting a higher microbial activity in response to phytase supplementation at lower phytase levels. Correspondingly, dry matter degradability was found to have improved in P540 and P720 compared to the control by 13 and 11% after 24h of incubation (P= 0.05). For ammonia nitrogen (NH3-N), a tendency towards lower values was only observed for P540 at 24h of fermentation (P= 0.07), while minimal treatment effects were observed at other fermentation times. The concentrations of total volatile fatty acids (VFA) were higher (P< 0.05) after 48h of fermentation for P540 and P720 compared to the control (P= 0.03) by 10% and 14%, respectively. Ruminal acetate tended towards higher values in the presence of phytase after 12h of fermentation (P= 0.10), but towards lower values after 24h of fermentation (P= 0.02), irrespective of the phytase dose applied. A trend towards lower ruminal propionate levels was observed in the presence of phytase after 6h (P= 0.10) and 12h (P= 0.06) of fermentation, while no effects were found at other fermentation times. In conclusion, phytase supplementation has the potential to improve metabolic energy activity of rumen microorganisms and the use of feed constituents. Thus, phytase supplementation could help to reduce environmental contamination in areas of ruminant production.

Enhancement of fermentative H2 production with peanut shell as supplementary substrate: Effects of acidification and buffer effect

For bio-H2 fermentation, the progress and H2 yield were significantly affected by culture pH. Our previous research found peanut shell powder (PSP, as supplementary substrate) having a buffer effect on the fermentative time prolongation and H2 yield enhancement. The acid buffer action (ABA), cation exchange capacity (CEC), scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were employed to explore the mechanism and structure changes of PSP. The superior ABA (57.44 ± 0.65 mmol/pH-kg) and CEC (112 ± 2.0 cmol/kg) of PSP, which provided high specific surface area and amorphous content, prolonged the fermentative time. The acidification of volatile fatty acids on PSP was effective to release reducing sugar and enhance hydrogen yield through breaking hemicellulose and amorphous components of cellulose, and enlarging specific surface area. The results indicated that buffer effect and acidification on PSP made positive effects on prolonging fermentation time and enhancing hydrogen yield.

In vitro fermentation of arabinoxylan from oat (Avena sativa L.) by Pekin duck intestinal microbiota.

Arabinoxylan (AX) is abundant in cereal grains used as feed for ducks. However, the duck intestinal microbes responsible for the degradation of AX are not fully understood. In this study, oat AX was degraded and utilized by different duck intestinal microbiota in vitro. Changes in short-chain fatty acids (SCFAs), branch-chain fatty acids, and the pH resulted from a 72-h AX fermentation in intestinal samples were measured. The addition of AX increased the concentration of isobutyric acid and decreased the concentrations of SCFAs. The pH values decreased significantly in the intestinal samples. Gut microbiota were assessed using high-throughput sequencing of the 16S ribosomal RNA gene, and the results indicated that AX stimulated the growth of Megamonas and Bifidobacterium species, with Megamonas exhibiting the greatest stimulation. Overall, the results suggest that oat AX is utilized by specific bacteria in duck intestines, providing the theoretical basis for the impacts of AX on animal health.

Hydrogen and electrical energy co-generation by a cooperative fermentation system comprising Clostridium and microbial fuel cell inoculated with port drainage sediment

This research work has succeeded in recovering energy from glucose by generating H2 with the aid of a Clostridium beijerinckii strain and obtaining electrical energy from compounds present in the H2 fermentation effluent in a microbial fuel cell (MFC) seeded with native port drainage sediment. In the fermentation step, 49.5% of the initial glucose concentration (56 mmol/L) was used to produce 104 mmol/L H2; 5, 33, 3, and 1 mmol/L acetate, butyrate, lactate, and ethanol also emerged, respectively. MFC tests by feeding the anodic compartment with acetate, butyrate, lactate (individually or as a mixture), or the H2 fermentation effluent provided power density values ranging between 0.6 and 1.2 W/m2. Acetate furnished the highest power density with a nanowire-rich biofilm despite the lowest anode bacterial concentration (1012 16S gene copies/g of sediment). Non-conventional exoelectrogenic microbial communities were observed in the acetate-fed MFC; e.g., Pseudomonadaceae (Pseudomonas) and Clostridia (Acidaminobacter, Fusibacter).

Fermentative H2 production from food waste: Parametric analysis of factor effects

Factorial fermentation experiments on food waste (FW) inoculated with activated sludge (AS) were conducted to investigate the effects of pH and the inoculum-to-substrate ratio (ISR [g VSAS/g TOCFW]) on biohydrogen production. The two parameters affected the H2 yield, the fermentation rate and the biochemical pathways. The minimum and maximum yields were 41 L H2/kg TOCFW (pH = 7.5, ISR = 1.74) and 156–160 L H2/kg TOCFW (pH = 5.5, ISR = 0.58 and 1.74). The range of carbohydrates conversion into H2 was 0.37–1.45 mol H2/mol hexose, corresponding to 9.4–36.2% of the theoretical threshold. A second-order predictive model for H2 production identified an optimum region at low pHs and high ISRs, with a theoretical maximum of 168 L H2/kg TOCFW at pH = 5.5 and ISR = 1.74. The Spearman’s correlation method revealed several relationships between the variables, suggesting the potentially governing metabolic pathways, which turned out to involve both hydrogenogenic pathways and competing reactions.

Enzymatically and/or thermally treated Macroalgae biomass as feedstock for fermentative H2 production

Due to its high carbohydrate content, algae biomass can be employed as feedstock to produce hydrogen (H2) by fermentation. However, to make the carbohydrates entrapped within the cell wall more bioavailable, algae biomass must be treated before fermentation. We submitted Kappaphyccus alvarezzi macroalgae biomass to autoclave (at 120 °C and 1 atm for 6 h) treatment and/or enzymatic (Celluclast® and/or a recombinant β- glucosidase) hydrolysis, to break down complex carbohydrates into available sugars that were used to produce H2 by fermentation. Macroalgae biomass treated with Celluclast®+β-glucosidase and with combined thermal treatment and enzymatic hydrolysis reached very similar TRS productivities, 0.24 and 0.22 g of TRS/L.h, respectively. The enzymatically treated biomass was employed as feedstock to produce H2 by Clostridium beijerinckii Br21, which afforded high yield: 21.3 mmol of H2/g of dry algae biomass. Hence, treatment with Celluclast® and recombinant β-glucosidase provided macroalgae biomass for enhanced bioconversion to H2 by C. beijerinckii Br21. Keywords: Kappaphyccus alvarezzi, Clostridium beijerinckii, Biohydrogen, Cellulase, β-glucosidase

Enhancement of biohydrogen production from sustainable orange peel wastes usingEnterobacterspecies isolated from domestic wastewater

Five facultative anaerobic bacterial isolates were recovered from domestic wastewater. These isolates were identified based on the 16S rRNA as Enterobacter aerogenes (one isolate), Enterobacter cloacae (two isolates), and Cronobacter sakazakii (three isolates). These isolates were examined for their potential to evolve hydrogen on a glucose medium. The most potent hydrogen-producing isolates, E aerogenes (KY549389) and E cloacae (KY524293), were examined for their capacity to generate hydrogen, acetone, butanol, and ethanol using orange peel (OP) hydrolysate. OP powder was pretreated with n-hexane to remove the toxicity of d-limonene. Different concentrations (4%, 6%, and 8% w/v) of limonene-free OP were subjected to the boiling water (temperature of 100°C) or acid (HCl) treatments. The maximum fermentative H2 production of 1700 and 1620 mL/L was obtained from 6% OP hydrolysate extracted with boiling water using facultative anaerobic E aerogenes (KY549389) and E cloacae (KY524293), respectively. Hydrogen production efficiency was 0.99 and 1.19 mol H2/mol glucose for E aerogenes and E cloacae, respectively. The total fermentative acetone, butanol, and ethanol (ABE) generated by E aerogenes and E cloacae were 0.78 and 0.38 g/L including acetone (0.05 and 0.04 g/L), butanol (0.011 and 0.013 g/L), and ethanol (0.71 and 0.32 g/L), respectively. The maximum ABE productivity was 0.01 and 0.005 g/L/h generated at 60 g/L OP hydrolysate by E aerogenes and E cloacae, respectively. These strains were positive for nitrogen fixation (nitrogenase) capability estimated by the acetylene reduction assay. Application of OP hydrolysate without the addition of any nutritional components or reducing agent is considered an eco-friendly, economical, and commercial substrate for desired biofuel production.

Thermophilic biohydrogen recovery from palm oil mill effluent

Enhancement of biological H2 production efficiency with pre-ozonation process of palm oil mill effluent (POME) prior to thermophilic dark fermentation (55 °C) was investigated. H2 fermentation experiments were conducted using varying concentrations of raw and ozonated POME. Results revealed that H2 can be produced from both raw and ozonated POME under thermophilic fermentation. Maximum H2 production yield of 77 mL.g−1CODremoved was obtained from ozonated POME, which was higher than that of 51 mL·g−1 CODremoved obtained from raw POME at the highest concentration of 35,000 mg COD.L−1. Meanwhile, the specific H2 production rate (R'max) of 1.9 and 1.5 mL·h−1·g−1 TVS were observed in raw and ozonated POME at the concentration of 25,000 mg COD.L−1, respectively. The main metabolic products during POME fermentation were acetic and butyric acids and trace amount of valeric acid. Propionic acid and ethanol have contributed, which could be reduced H2 production in all batch experiments for both POME. The highest efficiency of total and soluble COD removal of 24 and 25% was obtained from the raw POME, and those of 19 and 25% was obtained from the ozonated POME. The present study demonstrates that the POME loading was greatly influenced on the H2 production yields and rates. The comparative results showed that the ozonated POME gave higher H2 yields than the raw POME. Thus, demonstrating that the ozonation process significantly improved the POME biodegradability, which is able to enhance H2 production yields. However, the ozone pre-treatment was not improved in the specific H2 production rates.

Optimization of biohydrogen production of palm oil mill effluent by ozone pretreatment

The biohydrogen (H2) production in batch experiments under varying concentrations of raw and ozonated palm oil mill effluent (POME) of 5000–30,000 mg COD.L−1, at initial pH 6, under mesophilic (37 °C), thermophilic (55 °C) and extreme-thermophilic (70 °C) conditions. Effects of ozone pretreatment, substrate concentration and fermentation temperature on H2 production using mesophilic seed sludge was undertaken. The results demonstrated that H2 can be produced from both raw and ozonated POME, and the amounts of H2 production were directly increased as the POME concentrations were increased. H2 was successfully produced under the mesophilic fermentation of ozonated POME, with maximum H2 yield, and specific H2 production rate of 182 mL.g−1 CODremoved (30,000 mg COD.L−1) and 6.2 mL.h−1.g−1 TVS (25,000 mg COD.L−1), respectively. Thus, indicating that the ozone pretreatment could elevate on the biodegradability of major constituents of the POME, which significantly enhanced yields and rates of the H2 production. H2 production was not achieved under the thermophilic and extreme-thermophilic fermentation. In both fermentation temperatures with ozonated POME, the maximum H2 yield was 62 mL.g−1 CODremoved (30,000 mg COD.L−1) and 63 mL.g−1 CODremoved (30,000 mg COD.L−1), respectively. The highest efficiency of total and soluble COD removal was obtained at 44 and 37%, respectively following the mesophilic fermentation, of 24 and 25%, respectively under the thermophilic fermentation, of 32 and 20%, respectively under the extreme-thermophilic fermentation. The production of volatile fatty acids increased with an increased fermentation time and temperature in both raw and ozonated POME under all three fermentation temperatures. The accumulation of volatile fatty acids in the reactor content were mostly acetic and butyric acids. H2 fermentation under the mesophilic condition of 37 °C was the better selection than that of the thermophilic and extreme-thermophilic fermentation.

Ozonation aided mesophilic biohydrogen production from palm oil mill effluent

Ozone pretreatment of palm oil mill effluent (POME) was employed to improve sustrate biodegradability prior to biological H2 production. The H2 production was conducted at varing pHs from 4.0 to 6.0 to examine the impact of pH on the H2 mesophilic production (37 °C). The optimal pH for H2 production was 6.0 for both raw and ozonated POME. The POME concentrations were greatly influenced the yields and rates of H2 production. At the optimal pH, the maximum H2 production yield of 182 ± 7.2 mL.g−1 COD (7.96 mmoL.g−1 COD) was achieved at the ozonated POME concentration of 30,000 mg COD.L−1. The maximum H2 production rate (Rmax) of 43.1 ± 2.5 mL.h−1 was obtained at the ozonated POME concentration of 25,000 mg COD.L−1. The highest total COD removal was 44% at of 15,000 mg COD.L−1 ozonated POME. Acetic and butyric acids were dominant products during H2 fermentation and tended to increase with the increased POME concentrations. Ozonation as a pretreatment process showed significant enhancement of the POME biodegradability , and subsequently improved the H2 production H2.

Impact of glucose concentration on productivity and yield of hydrogen production by the new isolate Clostridium beijerinckii Br21

AbstractThis paper presents a detailed analysis of the batch kinetic fermentative assays data used to evaluate how glucose concentration influences fermentative H2 production, including the non‐dissociated acid concentration threshold, with the new isolate Clostridium beijerinckii Br21. Fermentative batch assays for hydrogen (H2) production were conducted with initial glucose concentrations of 5.2, 27.2, 54.4, 97.2, or 154.4 mmol/L without pH control. The dry cell mass (X), glucose (S), and product (H2) concentrations and the pH were monitored for 60 h. Increasing initial glucose concentration raised the maximum specific H2 production rate to values as high as 1.19 mmol H2/mg X · h. However, the H2 production yield (YH2/S) decreased from 2.23 to 0.2 mmol H2/mmol glucose. The initial glucose concentration that provided the best compromise between YH2/S and H2 productivity was 37 mmol/L (6.7 g/L). The lactic acid, acetic acid, and butyric acid concentrations enhanced at higher initial glucose concentrations, leading to the largest pH decrease. Lower pH favoured non‐dissociated acids, which switched the Clostridium metabolism to solventogenesis. The threshold acid concentrations for C. beijerinckii Br21 solventogenesis were non‐dissociated butyric acid at 8 mmol/L and total non‐dissociated acetic and butyric acids at 13 mmol/L. Glucose supply and pH control in continuous or fed‐batch biorreactors could culminate in higher H2 productivity and yield by C. beijerinckii Br21.

Impacts of different biochar types on hydrogen production promotion during fermentative co-digestion of food wastes and dewatered sewage sludge

Pyrolysis and anaerobic digestion are two important strategies for waste management that may be combined for clean energy production. This article investigates the effects of 12 types of biochars derived from four feedstocks at three pyrolysis temperatures on H2 production via fermentative co-digestion of food wastes and dewatered sewage sludge. The results show that feedstock type and pyrolysis temperature significantly influence biochar properties such as pH, specific surface area and ash contents. Despite the wide range of BET specific surface areas (1.2–511.3 m2/g) and ash contents (5.3–73.7(wt%)) of biochars produced, most biochars promoted the VFAs production process and altered the fermentative type from that of acetate type to butyrate type, which seemed to have a higher efficiency for H2 production. Moreover, fitting of the results to the modified Gompertz model shows that biochar addition shortens the lag time by circa 18–62% and increases the maximum H2 production rate by circa 18–110%. Furthermore, the biochar derived at higher pyrolysis temperatures enhances H2 production dramatically over those derived at low temperatures. Principal components analysis demonstrated that the pH buffering capacity of biochar was critical to the promotion of fermentative H2 production by mitigating the pH decrease caused by VFAs accumulation. Consequently, a sustainable integrated waste management strategy combining pyrolysis and anaerobic digestion is proposed for the efficient treatment of various bio-wastes.

Process kinetic studies of biohydrogen production by co-fermentation of fruit-vegetable wastes and cottage cheese whey

Hydrogen (H2) is considered as fuel for future and its biological production from renewable feedstocks is very promising. Dark fermentation of fruit-vegetable waste (FVW) and cottage cheese whey (CCW) for the production of H2 constitutes a promising way for combining energy generation and lignocellulosic waste management. In this work, process kinetics of biohydrogen production via dark fermentation of FVW and CCW by pretreated anaerobic sludge inocula were investigated. To inhibit H2 consuming methanogens, the effects of various inoculum pretreatment, viz., 2-bromoethanesulfonate, heat-shock, acid, alkali, UV, and ultrasonication on H2-production were investigated which revealed 2-bromoethanesulfonate, heat-shock and acid-treated inoculum resulted in maximum bioH2 production and yield of 118.12 ± 1.05, 93.37 ± 1.3, 96.32 mMol/L and 1.66, 1.22 ± 0.01, 1.39 ± 0.02 mMol/gCODinitial, respectively. The effects of system initial pH, substrate to inoculum (S0/X0) and carbon to nitrogen (C/N) ratio on H2-production were evaluated which revealed maximum H2 production and yield could be achieved at pH 7, S0/X0 of 10.6 gCOD/gVS, and C/N 26.8. Modified Gompertz model and Modified Logistic model were used to define various kinetic parameters pertaining to cumulative H2-production which showed high R2 values (≥0.98). The influence of pH on H2 and ethanol/volatile fatty acids production kinetics were evaluated using Andrew's and Ratkowsky's model showing relatively good R2 values (≥0.62). Remarkably high production of ethanol (2.43 ± 0.28 mg/L) was noticed alongside H2 production at pH 7 suggesting that bioethanol can be recovered at the end of fermentative H2 production. Terminal Restriction Fragment Length Polymorphism and 16s rDNA sequencing revealed dominance of 9 bacterial species such as Escherichia coli, Clostridium butyricum, Streptococcus henryi, and 6 others uncultured bacteroides. This research determined different kinetic parameters for an enhanced H2 production strategy by co-fermentation of FVW and CCW providing an understanding of process behavior which will in turn help in the upscaling of the H2-production processes.