Effect of ammonia on biohydrogen production from food waste via anaerobic fermentation

The effect of different additive ammonia (0–10 g/l as nitrogen) on hydrogen production from the anaerobic batch mesophilic fermentation of food waste was studied at two feed-to-microorganism ratios (F/M), 3.9 and 8.0. Anaerobic sludge taken from an anaerobic digester was used as inoculum. The hydrogen yield at F/M 3.9 and 8.0 without additive ammonia was 77.2 and 51.0 ml-H₂/gVS, respectively. At F/M 3.9, the hydrogen production was enhanced by adding additive ammonia in the system when the total ammonia nitrogen (TAN) concentration was no higher than 6.0 g/l. A maximum hydrogen yield of 121.4 ml-H₂/gVS was obtained at a TAN concentration of 3.5 g/l. At F/M 8.0, the enhancement of hydrogen production was found in a narrower range of additive TAN concentrations, with a highest yield of 60.9 ml-H₂/gVS at the TAN of 1.5 g/l. Hydrogen production was inhibited at higher additive TAN concentrations for both F/M ratios. This study provides a novel strategy for controlling ammonia for production of hydrogen from food waste via anaerobic fermentation.     

A bench scale study of fermentative hydrogen and methane production from food waste in integrated two-stage process

A two-stage fermentation process combining hydrogen and methane production for the treatment of food waste was investigated in this paper. In hydrogen fermentation reactor, the indigenous mixed microbial cultures contained in food waste were used for hydrogen production. No foreign inoculum was used in the hydrogen fermentation stage, the traditional heat treatment of inoculum was not applied either in this bench scale experiment. The effects of the stepwise increased organic loading rate (OLR) and solid retention time (SRT) on integrated two-stage process were investigated. At steady state, the optimal OLR and SRT for the integrated two-stage process were found to be 22.65 kg VS/m³ d (160 h) for hydrogen fermentation reactor and 4.61 (26.67 d) for methane fermentation reactor, respectively. Under the optimum conditions, the maximum yields of hydrogen (0.065 m³ H₂/kg VS) and methane (0.546 m³ CH₄/kg VS) were achieved with the hydrogen and methane contents ranging from 29.42 to 30.86%, 64.33 to 71.48%, respectively. Biodegradability analysis showed that 5.78% of the influent COD was converted to the hydrogen in H₂-SCRD and 82.18% of the influent COD was converted to the methane in CH₄-SCSTR under the optimum conditions.     

Biohydrogen generation from anaerobic digestion of food waste

Biohydrogen generated from the anaerobic digestion of a synthetic food waste with constant composition and a real food waste collected in Hong Kong were studied. This study aims at using a monoculture to increase biohydrogen production and determining optimum conditions for maximum biohydrogen production. Among the nine bacteria screened for biohydrogen production, Escherichia cloacae and Enterobacter aerogenes produced the largest amount of biohydrogen from the anaerobic digestion of synthetic food waste. The optimum anaerobic digestion conditions were determined: initial pH of 7, a water to solids ratio of 5 (w/w), a mesophilic temperature (37 ± 1 °C), and in the presence of 40 mg/L FeSO₄·7H₂O. Anaerobic digestion at the optimum operating conditions using collected food waste with E. cloacae as the bacterial source was also performed. By adjusting the pH in the range of 5–6, a specific biohydrogen production of 155.2 mL/g of volatile solids (VS) in food waste was obtained.     

Effect of food to microorganisms (F/M) ratio on biohythane production via single-stage dark fermentation

Hythane is a mixture of hydrogen and methane gases which are generally produced in separate ways. This work studied mesophilic biohythane gas (H₂+CH₄+CO₂) production in a bioreactor via single-stage dark fermentation. The fermentation was conducted in batch mode using mixed anaerobic microflora and food waste and condensed molasses fermentation soluble to elucidate the effects of food to microorganisms (F/M) ratio (ranging from 0.2 to 38.2) on gas production, metabolite variation, kinetics and biohythane-composition indicator performances. The experimental results indicate that the F/M ratio and fermentation time affect biohythane production efficiency with values of peak maximum hydrogen production rate 9.60 L/L-d, maximum methane production rate 0.72 L/L-d, and hydrogen yield (HY) of 6.17 mol H₂/kg COD_added. Depending on the F/M ratios, the H₂, CH₄ and CO₂ biogas components were 10–60%, 5–20% and 35–70%, respectively. Prospects for the further real application for single-stage biohythane fermentation based on the experimental data are proposed. This work characterizes an important reactor operation factor F/M ratio for innovative single-stage dark fermentation.     

Integrated Taguchi method and response surface methodology to confirm hydrogen production by anaerobic fermentation of cow manure

In the present study, we evaluated the feasibility of integrating the Taguchi method and the response surface methodology (RSM) to predict and optimize fermentative hydrogen production of cow manure (CM) slurry, a mixture of CM and tap water that was equivalent to 6% of the volatile solid (VS) content. Batch vial tests were first conducted in accordance with an experimental design using the Taguchi method L₁₈ orthogonal array that selected the significant influencing factors (temperature and pH) of hydrogen production, and then the RSM with a central composite design was used for the following experiments based on the aforementioned factors. Finally, fermentation experiments in triplicate were carried out in a 2-L semi-continuously stirred tank reactor (semi-CSTR) with a fixed organic loading rate (OLR), solid retention time (SRT) and varying temperatures and pH under a steady-state operation. Through a series of investigations conducted in this study, our experimental data confirmed that the optimal conditions were 60 °C with pH 5.20 ± 0.21, resulting in hydrogen content (HC) of 54.64 ± 11.45%, volumetric hydrogen production (VHP) of 405.54 ± 193.61 ml-H₂/l/d, and specific hydrogen yield (SHY) of 10.25 ± 4.96 ml-H₂/g-VS. This study demonstrates a good performance of the Taguchi method with pretests and the prediction of the response surfaces methodology. The confirmed experimental results show the behavior of anaerobic fermenters’ treating in significant factors, which will comply with management strategies for treatment of relative organic wastes in the future.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

Fermentative hydrogen production by diverse microflora

In this study, hydrogen production with activated sludge, a diverse bacterial source has been investigated and compared to microflora from anaerobic digester sludge, which is less diverse. Batch experiments were conducted at mesophilic (37 °C) and thermophilic (55 °C) temperatures. The hydrogen production yields with activated sludge at 37 °C and 55 °C were 0.56 and 1.32 mol H₂/mol glucose consumed, respectively. While with anaerobically digested sludge hydrogen yield was 2.18 mol H₂/mol glucose consumed at 37 °C and 1.25 mol H₂/mol glucose consumed at 55 °C. The results of repeated batch experiments for 615 h resulted in average yields of 1.21 ± 0.62 and 1.40 ± 0.16 mol H₂/mol glucose consumed for activated sludge and anaerobic sludge, respectively. The hydrogen production with activated sludge was not stable during the repeated batches and the fluctuation in hydrogen production was attributed to formation of lactic acid as the predominant metabolite in some batches. The presence of lactic acid bacteria in microflora was confirmed by PCR-DGGE.     

Seed inocula for biohydrogen production from biodiesel solid residues

This study aimed to optimize the hydrogen production from various seed sludges (two kinds of sewage sludges (S1, S2), cow dung (S3), granular sludge (S4) and effluent from condensed soluble molasses H₂ fermenter (S5)) and enhancement of hydrogen production via heat treatment for substrate and seed sludge by using the solid residues of biodiesel production (BDSR). Two batch assay tests were operated at a biodiesel solid residue concentration of 10 g/L, temperature of 55 °C and an initial cultivation pH of 8. The results showed that the peak hydrogen yield (HY) of 94.6 mL H₂/g volatile solid (VS) (4.1 mmolH₂/g VS) was obtained from S1 when substrate and seed sludge were both heat treated at 100 °C for 1 h. However, the peak hydrogen production rate (HPR) and specific hydrogen production rate (SHPR) of 1.48 L H₂/L-d and 0.30 L H₂/g VSS-d were obtained from S2 without any treatment. The heat treatment was found to increase the HY in both the cases of sewage sludges S1 and S2.The HY of 89.5 mL H₂/g VS (without treatment) was increased to 94.6 mL H₂/g VS and 82.6 mL H₂/g VS (without treatment) was increased to 85.7 mL H₂/g VS for S1 and S2. The soluble metabolic product (SMP) analysis showed that the fermentation followed mainly acetate–butyrate pathway with considerable production of ethanol. The total bioenergy production was calculated as 2.8 and 2.9 kJ/g VS for favorable hydrogen and ethanol production, respectively. The BDSR could be used as feedstock for dark fermentative hydrogen production.     

Feasibility of biohydrogen production by anaerobic co-digestion of food waste and sewage sludge

Anaerobic co-digestion of food waste and sewage sludge for hydrogen production was performed in serum bottles under various volatile solids (VS) concentrations (0.5–5.0%) and mixing ratios of two substrates (0:100–100:0, VS basis). Through response surface methodology, empirical equations for hydrogen evolution were obtained. The specific hydrogen production potential of food waste was higher than that of sewage sludge. However, hydrogen production potential increased as sewage sludge composition increased up to 13–19% at all the VS concentrations. The maximum specific hydrogen production potential of 122.9 ml/g carbohydrate-COD was found at the waste composition of 87:13 (food waste:sewage sludge) and the VS concentration of 3.0%. The relationship between carbohydrate concentration, protein concentration, and hydrogen production potential indicated that enriched protein by adding sewage sludge might enhance hydrogen production potential. The maximum specific hydrogen production rate was 111.2 ml H₂/g VSS/h. Food waste and sewage sludge were, therefore, considered as a suitable main substrate and a useful auxiliary substrate, respectively, for hydrogen production. The metabolic results indicated that the fermentation of organic matters was successfully achieved and the characteristics of the heat-treated seed sludge were similar to those of anaerobic spore-forming bacteria, Clostridium sp.     

Production of hydrogen and methane by one and two stage fermentation of food waste

Anaerobic digestion is an attractive process for generation of hydrogen and methane, which involves complex microbial processes on decomposition of organic wastes and subsequent conversion of metabolic intermediates to hydrogen and methane. Comparative performance of a sequential hydrogen and methane fermentation in two stage process and methane fermentation in one stage process were tested in batch reactor at varying ratios of feedstock to microbial inoculum (F/M) under mesophilic incubation. F/M ratios influence biogas yield, production rate, and potential. The highest H₂ and CH₄ yields of 55 and 94 mL g⁻¹ VS were achieved at F/M of 7.5 in two stage process, while the highest CH₄ yield of 82 mL g⁻¹ VS in one stage process was observed at the same F/M. Acetic and butyric acids are the main volatile fatty acids (VFAs) produced in the hydrogen fermentation stage with the concentration range 10–25 mmol L⁻¹. Little concentrations of VFAs were accumulated in methane fermentation in both stage processes. Total energy recovery in two stage process is higher than that in one stage by 18%. This work demonstrated two stage fermentation achieved a better performance than one stage process.     

Effect of temperature on anaerobic fermentative hydrogen gas production from feedlot cattle manure using mixed microflora

Hydrogen production from the anaerobic fermentation of feedlot cattle manure was examined in batch cultures over a temperature range from 36 to 60 °C at a pH of 5.2. The amount of hydrogen produced increased with temperature to a maximum of 65 L H₂ kg TS⁻¹ at 52 °C. At temperatures > 52 °C, acetate was the main volatile fatty acid (VFA) accumulated, while at <52 °C butyrate accumulated the most. Formate was detected in the 56 and 60 °C treatments but was absent in all others. Thermophilic conditions resulted in the highest hydrogen production rates, with maximum hydrogen production occurring 52 °C. Changing incubation temperature by small (4 °C) increments up or down from 52 °C resulted in changes in the metabolic flux (conversion of substrate to VFA and gaseous products) of the anaerobic digestion system. These findings indicate that the hydrogen production potential of anaerobic systems utilizing heat treated cattle manure as inoculum is affected greatly by incubation temperature.     

Hydrogen gas production from acid hydrolyzed wheat starch by combined dark and photo-fermentation with periodic feeding

Hydrogen gas production from acid hydrolyzed waste wheat starch by combined dark and photo-fermentation was investigated in continuous mode with periodic feeding and effluent removal. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides (NRRL-B 1727) were used as the seed culture for dark and light fermentations, respectively with biomass ratio of Rhodobacter/sludge = 3. Hydraulic residence time (HRT) was changed between 1 and 8 days by adjusting the feeding periods. Ground waste wheat was acid hydrolyzed at pH = 3 and 121 °C for 30 min using an autoclave and the resulting sugar solution was used as the substrate for combined fermentation after pH adjustment and nutrient addition. The highest daily hydrogen gas production (41 ml d⁻¹), hydrogen yield (470 ml g⁻¹ total sugar = 3.4 mol H₂ mol⁻¹glucose), volumetric and specific hydrogen production rates were obtained at the HRT of 8 days. The highest biomass and the lowest total volatile fatty acids (TVFA) concentrations were also realized at HRT = 8 days indicating VFA fermentation by Rhodobacter sp. at high HRTs. The lowest total sugar loading rate of 0.625 g L⁻¹ d⁻¹ resulted in the highest hydrogen yield and formation rate. Hydrogen gas production by combined fermentation with periodic feeding was proven to be an effective method resulting in high hydrogen yields at long HRTs.     

Viability of ultrasonication of food waste for hydrogen production

Batch anaerobic studies were conducted to study the effect of ultrasonication as a pre-treatment method for pulp waste prior to anaerobic hydrogen production. Pre-treatment was conducted by sonicating a 100 mL of pulp waste at different sonication times varying from 0.5 min to 30 min. The ultimate hydrogen production increased with increasing sonication time. The highest ultimate hydrogen production was achieved at a sonication time of 30 min and reflected an 88% increase over the unsonicated food waste, of 80 mL/g VS_added. The highest final VFAs concentration after fermentation (corresponding to 70% increase over the unsonicated food waste) was also achieved at a sonication time of 30 min. There were no significant differences between the acetate-to-butyrate ratios (HAc/HBu) for the all sonication times. The maximum hydrogen production rate at sonication time of 30 min was about 145% higher than that the unsonicated food waste.     

Continuous biohydrogen production from liquid swine manure supplemented with glucose using an anaerobic sequencing batch reactor

Liquid swine manure supplemented with glucose (10 g/L) was used as substrate for hydrogen production using an anaerobic sequencing batch reactor at 37 ± 1 °C and pH 5.0 under different hydraulic retention times (HRTs). Decreasing HRT from 24 to 8 h caused an increasing hydrogen production rate from 0.05 to 0.15 L/h/L. Production rates of both total biogas and hydrogen were linearly correlated to HRT with R² being 0.993 and 0.997, respectively. The hydrogen yield ranged between 1.18 and 1.63 mol-H₂/mol glucose and the 12 h HRT was preferred for high production rate and efficient yield. For all the five HRTs examined, the glucose utilization efficiency was over 98%. The biogas mainly consisted of carbon dioxide and hydrogen (up to 43%) with no methane detected throughout the experiment. Ethanol and organic acids were the major aqueous metabolites produced during fermentation, with acetic acid accounting for 56–58%. The hydrogen yield was found to be related to the acetate/butyrate ratio.     

Characteristics of biohydrogen fermentation from various substrates

The characteristics of biohydrogen production from sucrose, slurry-type piggery waste and food waste under the effects of the reactor configurations and operational pHs (6 and 9) were examined by using heat-treated anaerobic sludge as a seed biomass. When sucrose was used in the batch test, the maximum hydrogen yield was 0.12–0.13 g COD (as H₂)/g COD (1.41–1.43 mol/mol hexose) at pH 6. In contrast, 0.10–0.11 g COD (as H₂)/g COD (1.12–1.21 mol/mol hexose) hydrogen yield was achieved from the reactor at pH 9. On the other hand, hydrogen production was not observed in the continuous sequencing batch mode fermenters fed with sucrose. Profile analysis at each cycle revealed hydrogen production at the initial operation periods but eventually only methane at 36 days. When slurry-type piggery waste was used as the substrate, the upflow elutriation-type fermenters produced methane but not hydrogen after 30 days operation. The fermentation intermediate profile showed that the hydrogen produced might have been consumed by homoacetogenic or propionate producing reactions, and eventually converted into methane by acetoclastic methanogens. The downflow leaching bed fermenters using food waste produced 0.013 L H₂/g volatile solids (VS) (0.0061 g COD (as H₂)/g COD) at pH 6 with 54% VS reduction whereas 0.0041 L H₂/g VS (0.0020 g COD (as H₂)/g COD) was produced at pH 9 with 86% VS reduction. The results show that the hydrogen produced should be released rapidly from the reactor before it can be consumed in other biochemical reactions, and substrates with high pH level (>9.0) can be used directly to produce hydrogen without needing to adjust the pH.     

Efficient hydrogen gas production from cassava and food waste by a two-step process of dark fermentation and photo-fermentation

A two-step process of sequential anaerobic (dark) and photo-heterotrophic fermentation was employed to produce hydrogen from cassava and food waste. In dark fermentation, the average yield of hydrogen was approximately 199 ml H₂ g⁻¹ cassava and 220 ml H₂ g⁻¹ food waste. In subsequent photo-fermentation, the average yield of hydrogen from the effluent of dark fermentation was approximately 611 ml H₂ g⁻¹ cassava and 451 ml H₂ g⁻¹ food waste. The total hydrogen yield in the two-step process was estimated as 810 ml H₂ g⁻¹ cassava and 671 ml H₂ g⁻¹ food waste. Meanwhile, the COD decreased greatly with a removal efficiency of 84.3% in cassava batch and 80.2% in food waste batch. These results demonstrate that cassava and food waste could be ideal substrates for bio-hydrogen production. And a two-step process combining dark fermentation and photo-fermentation was highly improving both bio-hydrogen production and removal of substrates and fatty acids.     

Biohydrogen production by anaerobic co-digestion of municipal food waste and sewage sludges

Food waste (FW), primary sludge (PS) and waste activated sludge (WAS) were characterized and found to be complementary in the concentrations of carbohydrates, total Kjeldahl nitrogen (TKN), PO₄–P and some metal for biological hydrogen production. Moreover, FW was found to have low pH buffering capacity while the values for PS and WAS were relatively higher. An anaerobic toxicity analysis (ATA) derived from a methanogenic ATA protocol showed that these waste materials had no toxicity to hydrogen production. Adding phosphate buffer to the FW significantly improved hydrogen production while initial pH was 7.0. Co-digestion of FW and sewage sludge was studied using a batch respirometric cultivation system. All combinations of the feedstocks (FW+PS, FW+WAS and FW+PS+WAS) showed enhanced hydrogen production potential as compared with the individual wastes. A mixing ratio of 1:1 was found to be the best among the ratios tested for all three co-digestion groups. A hydrogen yield of 112 mL/g volatile solid (VS) added was obtained from a combination of FW, PS and WAS. This yield was equivalent to 250 mL/g VS added if only FW contributed to hydrogen production. The reason for the enhancement of hydrogen production was postulated to be multifold in which the increase in buffer capacity in the co-digestion mixture was verified.     

Effects of sludge pre-treatment method on bio-hydrogen production by dark fermentation of waste ground wheat

Three different pre-treatment methods were applied on two different anaerobic sludge cultures and their mixtures in order to investigate the effects of pre-treatment methods on bio-hydrogen production from dark fermentation of waste ground wheat solution. Repeated heat, chloroform and combinations of heat and chloroform pre-treatment methods were applied to anaerobic sludges from different sources. Repeated heat treatment (2 × 5 h) was found to be more effective in selecting hydrogen producing bacteria compared to the other treatment methods tested on the basis of cumulative hydrogen production. The highest hydrogen formation (652 ml) and specific hydrogen production rate (SHPR = 25.7 ml H₂ g⁻¹ cells h⁻¹) were obtained with the anaerobic sludge pre-treated by repeated boiling. Both the type of anaerobic sludge and the pre-treatment method had considerable effects on bio-hydrogen production from wheat powder solution (WPS) by dark fermentation.     

Fermentative hydrogen production from lipid-extracted microalgal biomass residues

The conversion of lipid-extracted microalgal biomass residues (LMBRs) into hydrogen plays the dual role in renewable energy production and sustainable development of microalgal biodiesel industry. An anaerobic fermentation process to covert LMBRs into hydrogen was investigated in this work. Using batch experiments, the effects of pretreatment of inoculum (by acid, base, heat, and chloroform, respectively), initial pH (5.0–7.0), inoculum concentrations at 0.59–2.94 g VSS/l (volatile suspended solids, VSS) and substrate concentrations at 4.5–45 g VS/l (volatile solids, VS) were investigated, respectively. The results showed that the most effective hydrogen production was obtained from fermentation of LMBRs with a concentration of 36 g VS/l at the initial pH 6.0–6.5 using the heat-treated anaerobic digested sludge as inoculum. Acetate, propionate and butyrate were the main fermentation byproducts in the conversion of LMBRs into hydrogen.     

Effect of fermentation conditions on biohydrogen production from lipid-rich food material

Among the basic components of organic materials, such as carbohydrate, protein, and lipid, the hydrogen yield of carbohydrate fermentation has been reported to be significantly higher than that of lipid. This study used lard as a model organic matter for lipid and investigated its H₂ production potential in batch anaerobic fermentation experiments under various combinations of stirring and CO₂-scavenging conditions. A significant increase in the hydrogen yield was observed in both CO₂-scavenging and stirring conditions; the CO₂-scavenging condition yield was 2.9 times higher than the stirring condition (116.7 and 40.3 mL H₂/g volatile solid [VS], respectively), which was much greater than reported previously. A maximal hydrogen yield of 185.8 mL H₂/g VS was obtained in the presence of both CO₂-scavenging and stirring, and the H₂ content of the total biogas was as high as 99% (v/v). In addition, there was less H₂ and more CH₄ production in the absence of CO₂-scavenging and/or stirring, which suggests that the consumption of H₂ and CO₂ for methanogenesis was the major mechanism of the poor hydrogen yield from lipid. The volatile fatty acids in all the tests consisted primarily of valeric (47.2–54.9%) and propionic acids (26.6–30.3%), and higher concentrations of these acids remained in the fermentation liquid without CO₂ removal. These results suggest that lipid-rich food waste is a potential source for H₂ production if the fermentation process is optimized to minimize the partial pressure of CO₂ and H₂ and restrain the activities of H₂-consuming bacteria.