Bio-hydrogen production by photo-fermentation of dark fermentation effluent with intermittent feeding and effluent removal

Pure culture of Rhodobacter sphaeroides (NRRL- B1727) was used for continuous photo-fermentation of volatile fatty acids (VFA) present in the dark fermentation effluent of ground wheat starch. The feed contained 1950 ± 50 mg L⁻¹ total VFA with some nutrient supplementation. Hydraulic residence time (HRT) was varied between 24 and 120 hours. The highest steady-state daily hydrogen production (55 ml d⁻¹) and hydrogen yield (185 ml H₂ g⁻¹ VFA) were obtained at HRT = 72 hours (3 days). Biomass concentration increased with increasing HRT. Volumetric and specific hydrogen formation rates were also maximum at HRT = 72 h. High extent of TVFA fermentation at HRT = 72 h resulted in high hydrogen gas production.     

Photo-fermentative hydrogen gas production from dark fermentation effluent of ground wheat solution: Effects of light source and light intensity

Dark fermentation effluent of wheat powder solution was subjected to light fermentation for bio-hydrogen production using different light sources and intensities. Tungsten, fluorescent, infrared (IR), halogen lamps were used as light sources with a light intensity of 270 Wm⁻² along with sunlight. Pure culture of Rhodobacter sphaeroides-RV was used in batch light fermentation experiments. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (CHF, 252 ml) and yield (781 ml H₂ g⁻¹ TVFA). In the second set of experiments, light fermentations were performed at different light intensities (1–10 klux) using halogen lamp. The optimum light intensity was found to be 5 klux (approx. 176 Wm⁻²) resulting in the highest CHF (88 ml) and hydrogen yield (1037 ml H₂ g⁻¹TVFA). Hydrogen formation was limited by the availability of light at low light intensities below 5 klux and was inhibited by the excess light above 5 klux.     

Thermophilic dark fermentation of acid hydrolyzed waste ground wheat for hydrogen gas production

Batch dark fermentation experiments were performed to investigate the effects of biomass and substrate concentration on bio-hydrogen production from acid hydrolyzed ground wheat at 55 °C. In the first set of experiments, the substrate concentration was constant at 20 g total sugar L⁻¹ and biomass concentration was varied between 0.52 and 2.58 g L⁻¹. Total sugar concentration was varied between 4.2 and 23.7 g L⁻¹ in the second set of experiments with a 1.5 g L⁻¹ constant biomass concentration. The highest cumulative hydrogen formation (582 mL, 30 °C, 1 atm), formation rate (5.43 mL h⁻¹) and final total volatile fatty acid (TVFA) concentration (6.54 g L⁻¹) were obtained with 1.32 g L⁻¹ biomass concentration. In variable substrate concentration experiments, the highest cumulative hydrogen (365 mL) and TVFA concentration (4.8 g L⁻¹) were obtained with 19.25 g L⁻¹ initial total sugar concentration while hydrogen gas formation rate (12.95 mL h⁻¹) and the yield (200 mL H₂ g⁻¹ total sugar) were the highest with 4.2 g L⁻¹ total sugar concentration.     

Photo-fermentative hydrogen gas production from dark fermentation effluent of acid hydrolyzed wheat starch with periodic feeding

Hydrogen gas production by photo-fermentation of dark fermentation effluent of acid hydrolyzed wheat starch was investigated at different hydraulic residence times (HRT = 1-10 days). Pure Rhodobacter sphaeroides (NRRL B-1727) culture was used in continuous photo-fermentation by periodic feeding and effluent removal. The highest daily hydrogen gas production (85 ml d⁻¹) was obtained at HRT = 4 days (96 h) while the highest hydrogen yield (1200 ml H₂ g⁻¹ TVFA) was realized at HRT = 196 h. Specific and volumetric hydrogen formation rates were also the highest at HRT = 96 h. Steady-state biomass concentrations and biomass yields increased with increasing HRT. TVFA loading rates of 0.32 g L⁻¹ d⁻¹ and 0.51 g L⁻¹ d⁻¹ resulted in the highest hydrogen yield and formation rate, respectively. Hydrogen gas yield obtained in this study compares favorably with the relevant literature reports probably due to operation by periodic feeding and effluent removal.     

Photofermentative hydrogen production from volatile fatty acids present in dark fermentation effluents

In the present study, the growth and hydrogen production of Rhodobacter sphaeroides O.U. 001, was investigated in media containing five different volatile fatty acids (VFA) individually (malate, acetate, propionate, butyrate and lactate) and in media containing mixtures of these acids that reflect the composition of dark fermentation effluents. The highest hydrogen production rate was obtained in malate (24 ml_hydrogen/l_reactor h) and the highest biomass concentration was obtained in acetate containing media (1.65 g/l). The substrate conversion efficiencies for different volatile fatty acids were found to vary between 14 and 50%. The malate and butyrate consumption rates were first order with consumption rate constants of 0.026 h⁻¹ and 0.015 h⁻¹, respectively. In the case of substrate mixtures, it was observed that the bacteria consumed acetate first, followed by propionate and then butyrate. It was also found that the consumption rate of the main substrate significantly increased when the minor substrates were depleted.     

Hydrogen production from agricultural waste by dark fermentation: A review

The degradation of the natural environment and the energy crisis are two vital issues for sustainable development worldwide. Hydrogen is considered as one of the most promising candidates as a substitute for fossil fuels. In this context, biological processes are considered as the most environmentally friendly alternatives for satisfying future hydrogen demands. In particular, biohydrogen production from agricultural waste is very advantageous since agri-wastes are abundant, cheap, renewable and highly biodegradable. Considering that such wastes are complex substrates and can be degraded biologically by complex microbial ecosystems, the present paper focuses on dark fermentation as a key technology for producing hydrogen from crop residues, livestock waste and food waste. In this review, recent findings on biohydrogen production from agricultural wastes by dark fermentation are reported. Key operational parameters such as pH, partial pressure, temperature and microbial actors are discussed to facilitate further research in this domain.     

Fungal solid-state fermentation of food waste for biohydrogen production by dark fermentation

The dark fermentation process was evaluated for biohydrogen production from food waste through fungal solid-state fermentation (SSF). Three fungal cultures (one strain of Aspergillus tubingensis and two strains of Meyerozyma caribbica) were compared, being A. tubingensis the best hydrolyser culture for releasing soluble carbohydrates. The biochemical hydrogen potential of food waste hydrolysate (FWH) at different substrate-inoculum ratios obtained a lower hydrogen yield than untreated food waste (RFW). The highest hydrogen yield value corresponded to treatments RFW-20 and RFW-30 with 77.0 ± 2.6 and 76.9 ± 1.4 mL H₂ normalized by per gram volatile solid added (NmL H₂/gVS_added), respectively. The microbial community of food waste was analysed, being detected lactic-acid bacteria genera as Latilactobacillus and Leuconostoc. The presence of actively growing bacteria during the SSF could explain the lowest hydrogen yield (20.1–36.0 NmL H₂/gVS_added) in the FWH treatment due to the substrate competition between lactic-acid bacteria and hydrogen-producing bacteria, where the lactic-acid bacteria were favoured by their faster growth rate.     

Microbial culture selection for bio-hydrogen production from waste ground wheat by dark fermentation

Hydrogen formation performances of different anaerobic bacteria were investigated in batch dark fermentation of waste wheat powder solution (WPS). Serum bottles containing wheat powder were inoculated with pure cultures of Clostridium acetobutylicum (CAB), Clostridium butyricum (CB), Enterobacter aerogenes (EA), heat-treated anaerobic sludge (ANS) and a mixture of those cultures (MIX). Cumulative hydrogen formation (CHF), hydrogen yield (HY) and specific hydrogen production rate (SHPR) were determined for every culture. The heat-treated anaerobic sludge was found to be the most effective culture with a cumulative hydrogen formation of 560 ml, hydrogen yield of 223 ml H₂ g⁻¹ starch and a specific hydrogen production rate of 32.1 ml H₂ g⁻¹ h⁻¹.     

Effect of food to microorganism ratio on biohydrogen production from food waste via anaerobic fermentation

The effect of different food to microorganism ratios (F/M) (1–10) on the hydrogen production from the anaerobic batch fermentation of mixed food waste was studied at two temperatures, 35 ± 2 °C and 50 ± 2 °C. Anaerobic sludge taken from anaerobic reactors was used as inoculum. It was found that hydrogen was produced mainly during the first 44 h of fermentation. The F/M between 7 and 10 was found to be appropriate for hydrogen production via thermophilic fermentation with the highest yield of 57 ml-H₂/g VS at an F/M of 7. Under mesophilic conditions, hydrogen was produced at a lower level and in a narrower range of F/Ms, with the highest yield of 39 ml-H₂/g VS at the F/M of 6. A modified Gompertz equation adequately (R² > 0.946) described the cumulative hydrogen production yields. This study provides a novel strategy for controlling the conditions for production of hydrogen from food waste via anaerobic fermentation.     

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.     

Scaling-up bio-hydrogen production from food waste: Feasibilities and challenges

Hydrogen has potential as a renewable energy source due to its outstanding clean energy content. The production of hydrogen from food waste by dark fermentation gains attention from researchers across the world as it requires lower energy and chemicals compared to other chemical routes, not to mention that the use of food waste as raw material could help lessen the global waste dumping crisis. Currently, the knowledge of hydrogen production from food waste by dark fermentation is still limited in a laboratory scale. This article intends to provide up-to-date status quo on this technology. Factors affecting production potential, appropriate condition of production, feasibility of scaled-up production and economic value analysis of such technology is summarized and analyzed.     

Non-sterile bio-hydrogen fermentation from food waste in a continuous stirred tank reactor (CSTR): Performance and population analysis

Bio-hydrogen production from food waste by anaerobic mixed cultures was conducted in a continuous stirred tank reactor (CSTR). The hydraulic retention time (HRT) was optimized in order to maximize hydrogen yield (HY) and hydrogen production rate (HPR). The maximum hydrogen content (38.6%), HPR (379 mL H₂/L. d) and HY (261 mL H₂/g-VS_added) were achieved at the optimum HRT of 60 h. The major soluble metabolite products were butyric and acetic acids which indicated a butyrate-acetate type fermentation. Operation of CSTR at HRT 60 h could select hydrogen producing bacteria and eliminate lactic acid bacteria and acetogenic bacteria. The microbial community analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) revealed that the predominant hydrogen producer was Clostridium sp.     

An investigation on the dose-dependent effect of iron shaving on bio-hydrogen production from food waste

Bio-hydrogen production is of significant interest as it is capable of consuming waste material and synthesizing hydrogen which is a green gas. In this study, we examined the dose-dependent effect of iron shaving on bio-hydrogen production from an integrated dark and photo fermentation system from an artificial food waste. Overall, introduction of iron shaving enhanced the bio-gas production. Statistical analysis was performed on the extracted parameters obtained from fitting the experimental data to Gompertz function, revealing that the bio-gas production can be significantly enhanced by addition of iron shaving at concentrations up to 500 mg/L, with a maximum enhancement at 200 mg/mL. GC analysis showed that introduction of iron shaving at 200 mg/L also maximized the hydrogen percentage in the produced bio-gas. Based on the HPLC results, it was postulated that the dark-fermentation step was probably the step that was more affected by the introduction of iron shaving. Investigation of the pH showed that the acidification of the solution approximately coincided with the termination of the process. Our finding suggests that a more efficient buffer-assisted setup can significantly enhance the bio-hydrogen efficiency.     

Direct hydrogen production from cellulosic waste materials with a single-step dark fermentation process

Biohydrogen production from cellulosic waste materials using dark fermentation is a promising technology for producing renewable energy. The purpose of this study was to evaluate residual cellulosic materials generated from local sources for their H₂ production potential without any pretreatment. Clostridium thermocellum ATCC 27405, a cellulolytic, thermophilic bacterium that has been shown to be capable of H₂ production on both cellobiose and α-cellulose substrates, was used in simultaneous batch fermentation experiments with dried distillers grain (DDGs), barley hulls (BH) and fusarium head blight contaminated barley hulls (CBH) as the carbon source. Overall, the dried distillers grain produced the highest concentration of hydrogen gas at 1.27 mmol H₂/glucose equivalent utilized. CBH and BH produced 1.18 and 1.24 mmol H₂/glucose equivalent utilized, respectively. Overall, this study indicates that hydrogen derived from a variety of cellulosic waste biomass sources is a possible candidate for the development of sustainable energy.     

Effects of light source,intensity and lighting regime on bio-hydrogen production from ground wheat starch by combined dark and photo-fermentations

Combined dark and photo-fermentation of ground wheat starch was carried out by using different light sources, intensities and lighting regime. A mixture of heat treated anaerobic sludge and Rhodobacter sphaeroides-RV with a certain light/dark bacteria ratio was used in batch experiments. Tungsten, fluorescent, infrared (IR), tungsten + infrared, halogen lamps were used as light sources with a light intensity of 270 Wm⁻² along with sunlight. Halogen lamp was found to be the most suitable light source yielding the highest cumulative hydrogen formation (178 ml) and yield (218 ml g⁻¹ starch). Combined fermentations were performed at different light intensities (1–10 klux) using the halogen lamp in the second set of experiments. The optimum light intensity was found to be 10 klux (approx. 352 Wm⁻²) resulting in the highest cumulative hydrogen (111 ml) and hydrogen yield (139 ml H₂ g⁻¹ starch). Hydrogen formation was limited by the availability of light at low light intensities below 10 klux. Durations of dark/light cycles were changed to determine the most suitable lighting regime. Hydrogen gas formation increased with increasing cycle time and continuous lighting resulted in the highest cumulative hydrogen formation and hydrogen yield.     

Kinetic study of biological hydrogen production by anaerobic fermentation

The growth kinetics of hydrogen producing bacteria using three different substrates, namely sucrose, non-fat dry milk (NFDM), and food waste were investigated in dark fermentation through a series of batch experiments. The results showed that hydrogen production potential and hydrogen production rate increased with an increasing substrate concentration. The maximum hydrogen yields from sucrose, NFDM, and food waste were 234, 119, and 101 mL/g COD, respectively. The low pH (pH<4)$(\mathrm{pH}<4)$ inhibited hydrogen production and resulted in lower carbohydrate fermentation at high substrate concentration. Michaelis–Menten equation was employed to model the hydrogen production rate at different substrate concentrations. The equation gave a good approximation of the maximum hydrogen production rate and the half saturation constant (_Ks)$(K_{\mathrm{s}})$ with correlation coefficient (R²)$(R^2)$ over 0.85. The _Ks$K_{\mathrm{s}}$ values of sucrose, NFDM, and food waste were 1.4, 6.6, and 8.7 g COD/L, respectively. Based on _Ks$K_{\mathrm{s}}$ values, the substrate affinity of the enriched hydrogen producing culture was found to depend on carbohydrate content of the substrate. The substrate containing high carbohydrate showed a lower _Ks$K_{\mathrm{s}}$ value. The maximum hydrogen production rate was governed by the complexity of carbohydrates in the substrate.     

Dark fermentative hydrogen production from food waste: Effect of biomass ash supplementation

This work aimed to investigate the effects of supplementing two distinct types of ash, namely fly ash (FA) and bottom ash (BA) on the dark fermentation (DF) process of food waste (FW) for H₂ production. Both types of biomass combustion ash (BCA) were collected in an industrial bubbling fluidized bed combustor, using residual forest biomass as fuel. Results indicated that adding BCA at different doses of 1, 2 and 4 g/L could effectively enhance H₂ generation when compared to the control test without BCA addition. This stimulatory effect was attributed to the crucial role of metal elements released from BCA such as sodium, potassium, calcium, magnesium, and iron in the provision of buffering capacity and inorganic nutrients for the functioning of hydrogen-forming bacteria. The highest H₂ yield of 169 mL per g of volatile solids (VS) were obtained by adding only a small amount of BA (1 g/L) to the reactive system, representing a significant increment of 1070% compared to the control reactor. Furthermore, a significant decrease in the bacterial lag phase time from 26 h to 2.7 h, as well as about a 12-fold increase in the energy recovery as H₂ gas was observed at BA dosage of 1 g/L in comparison with the control reactor. Overall, this study suggested that a proper addition of BCA could promote the DF process of FW and enhance biohydrogen production.     

Development of a simple bio-hydrogen production system through dark fermentation by using unique microflora

In order to ensure efficient functioning of hydrogen fermentation systems that use Clostridium as the dominant hydrogen producer, energy-intensive process such as heat pretreatment of inoculum and/or substrate, continuous injection, and control of anaerobic conditions are required. Here, we describe a simple hydrogen fermentation system designed using microflora from leaf-litter cattle-waste compost. Hydrogen and volatile fatty acid production was measured at various hydraulic retention times, and bacterial genera were determined by PCR amplification and sequencing. Although hydrogen fermentation yield was approximately one-third of values reported in previous studies, this system requires no additional treatment and thus may be advantageous in terms of cost and operational control. Interestingly, Clostridium was absent from this system. Instead, Megasphaera elsdenii was the dominant hydrogen-producing bacterium, and lactic acid-producing bacteria (LAB) were prevalent. This study is the first to characterize M. elsdenii as a useful hydrogen producer in hydrogen fermentation systems. These results demonstrate that pretreatment is not necessary for stable hydrogen fermentation using food waste.     

Dark fermentative hydrogen gas production from waste peach pulp by intermittent feeding: Effects of hydraulic residence time and substrate loading rate

Peach has a big share of the world fruit market, with significant annual waste production. This study reports dark fermentative hydrogen gas production from waste peach pulp using intermittent feeding. In this context, the effects of hydraulic residence time (HRT) and substrate loading rate (SLR) on hydrogen production were determined in two sets of experiments. All experiments were performed in 310 mL serum bottles. During the first set of experiments, HRT was varied between 1 and 6 days and hydrogen production was more favorable at short HRTs. In the second set of experiments, SLR was varied between 9 and 90 gTOC/L.d, and more efficient hydrogen formation was observed by increasing the SLR. The most convenient HRT and SLR resulting in maximum hydrogen formation rate (931.8 mLH₂/L.d) was obtained at 1 day and 90 gTOC/L.d, respectively.