Effect of hydraulic retention time on biohydrogen production from palm oil mill effluent in anaerobic sequencing batch reactor

The feasibility of hydrogen generation from palm oil mill effluent (POME), a high strength wastewater with high solid content, was evaluated in an anaerobic sequencing batch reactor (ASBR) using enriched mixed microflora, under mesophilic digestion process at 37 °C. Four different hydraulic retention times (HRT), ranging from 96 h to 36 h at constant cycle length of 24 h and various organic loading rate (OLR) concentrations were tested to evaluate hydrogen productivity and operational stability of ASBR. The results showed higher system efficiency was achieved at HRT of 72 h with maximum hydrogen production rate of 6.7 LH₂/L/d and hydrogen yield of 0.34 LH₂/g COD_feeding, while in longer and shorter HRTs, hydrogen productivity decreased. Organic matter removal efficiency was affected by HRT; accordingly, total and soluble COD removal reached more than 37% and 50%, respectively. Solid retention time (SRT) of 4-19 days was achieved at these wide ranges of HRTs. Butyrate was found to be the dominant metabolite in all HRTs. Low concentration of volatile fatty acid (VFA) confirmed the state of stability and efficiency of sequential batch mode operation was achieved in ASBR. Results also suggest that ASBR has the potential to offer high digestion rate and good stability of operation for POME treatment.     

Biohydrogen production from hydrolyzed waste wheat by dark fermentation in a continuously operated packed bed reactor: The effect of hydraulic retention time

The aim of the study is biohydrogen production from hydrolyzed waste wheat by dark fermentation in a continuously operated up-flow packed bed reactor. For this purpose, the effect of hydraulic retention time (HRT) on the rate (R_H2) and yield (Y_H2) of hydrogen gas formation were investigated. In order to determine the most suitable hydraulic retention time yielding the highest hydrogen formation, the reactor was operated between HRT = 1 h and 8 h. The substrate was the acid hydrolyzed wheat powder (AHWP). Waste wheat was sieved down to 70 μm size (less than 200 mesh) and acid hydrolyzed at pH = 2 and 90 °C in an autoclave for 15 min. The sugar solution obtained from hydrolysis of waste wheat was used as substrate at the constant concentration of 15 g/L after neutralization and nutrient addition for biohydrogen production by dark fermentation. The microbial growth support particle was aquarium biological sponge (ABS). Heat-treated anaerobic sludge was used as inoculum. Total gas volume and hydrogen percentage in total gas, hydrogen gas volume, total sugar and total volatile fatty acid concentrations in the feed and in the effluent of the system were monitored daily throughout the experiments. The highest yield and rate of productions were obtained as Y_H2 = 645.7 mL/g TS and R_H2 = 2.51 L H₂/L d at HRT = 3 h, respectively.     

Feedback control strategy for optimizing biohydrogen production from organic solid waste in a discontinuous process

The use of control strategies for the biological process of hydrogen (H₂) production can increase productivity, stability, and robustness, increasing the viability of the implementation of these systems at the industrial level. A feedback control strategy for optimizing biohydrogen production from organic solid waste in a discontinuous process was proposed and pragmatically tested. The control strategy, which is based on recursively fitting a modified Gompertz model to gathered online data of the cumulative H₂ volume, could eventually stabilize the system at an optimal reaction time. The control strategy was evaluated during 140 degradation cycles maintaining a stable H₂ production with a reproducible form in the cumulative H₂ production curve. Independent of the changes in the microbial population dynamics in the reactor, the control strategy maintained a stable H₂ production avoiding the presence of methanogenic archaea. With the proposed controller, a compromise between the needed HRT and the H₂ production was obtained.     

Effect of pre-treatment and hydraulic retention time on biohydrogen production from organic wastes

This study investigated the effect of pre-treatment and hydraulic retention time (HRT) on biohydrogen production from organic wastes. Various pre-treatments including thermal, base, acid, ultrasonication, and hydrogen peroxide were applied alone or in combination to enhance biohydrogen production from potato and bean wastewater in batch tests. All the pre-treated samples showed higher hydrogen production than the control tests. Hydrogen peroxide pre-treatment achieved the best results of 939.7 and 470 mL for potato and bean wastewater, respectively. Continuous biohydrogen production from sucrose, potato and bean wastewater was significantly influenced by reducing the HRT as 24, 18 and 12 h. Sucrose and potato showed similar behavior, where the hydrogen production rate (HPR) increased with decreasing the HRT. Optimum hydrogen yield results of 320 mL-H₂/g-VS (sucrose) and 150 mL-H₂/g-VS (potato) were achieved at HRT of 18 h. Bean wastewater showed optimum HPR of 0.65 L/L.d with hydrogen yield of 80 mL-H₂/g-VS at 24 h HRT.     

The use of acidified palm oil mill effluent for thermophilic biomethane production by changing the hydraulic retention time in anaerobic sequencing batch reactor

The feasibility of thermophilic biomethane production from acidified palm oil mill effluent (POME) was assessed in a 5 L anaerobic sequencing batch reactor (ASBR). The effects of various hydraulic retention time (HRT) (10-1 d) on methane production performance and the stability of ASBR in treating acidified POME were evaluated herein. It was found that the highest methane productivity of 5.65 L CH₄/L/d could be attained at HRT of 2 d. However, the removal of chemical oxygen demand (COD) and volatile fatty acid (VFA) at this HRT is rather low (65-62%) hence making it inefficient to operate at HRT 2 d since most of the contaminants remained in the liquid streams. Thus the most recommended HRT was 3 d with maximum methane productivity of 3.96 L CH₄/L/d with corresponding methane yield of 260.3 L CH₄/kgCOD_removed. The COD removal efficiency at 3 d HRT was 71%, and the VFA consumption was more than 80%. The correlation of total VFA: total alkalinity (TVFA: TA) at HRT of 3 d was found to be 0.1. This recommended HRT of 3 is equally shorter than any previously reported application of POME as a substrate for thermophilic biomethane.     

Catalytic biohydrogen production from organic waste materials: A literature review and bibliometric analysis

Global population growth and accelerated urbanisation have resulted in massive amounts of fossil fuel use and waste production. Because of its high energy content, pure nature, and fuel quality, hydrogen fuel is a viable option to fossil fuels. Biohydrogen from agricultural waste, in particular, piques concern because it generates hydrogen while still disposing of waste. This review conducted a bibliometric analysis of biohydrogen production from organic waste to trace the research trends and hotspots based on the literature in the Web of Science (WOS) database from 1970 to 2020. The present review article also focuses on highlighting various processes for converting organic waste into hydrogen, raw materials for biohydrogen production, and catalysts that could distil the latest perceptions that could shed light on a route advancing for successful catalyst design. It also seems that some intentions have been paid on studying waste materials such as pure polysaccharides, disaccharides, and monosaccharides. Among all the catalysts used, non-noble and low-cost active metals over reduced graphene oxide (rGO) support can significantly affect the activity of fermentative hydrogen production from organic waste materials. However, researches focusing on developing anaerobic membrane bioreactors for these technologies are still needed.     

Biohydrogen production in the two-stage process of anaerobic bioconversion of organic matter of liquid organic waste with recirculation of digister effluent

At present, hydrogen energy is gaining immense popularity in the world due to the problem of depletion of non-renewable energy sources, hydrocarbons, and environmental pollution caused by their growing consumption. Of particular interest is the dark process of producing hydrogen-containing biogas in the processing of organic waste under anaerobic conditions which allows to take advantage of both energy production and solving the problem of recycling organic waste. The article describes in detail an experimental plant for investigating a two-stage process of anaerobic bioconversion of organic matter of liquid organic waste and setting up an experiment to study the effect of recirculation of the methantenk effluent into an anaerobic bioreactor for the production of biohydrogen. Moreover, experimental studies were carried out in a continuous mode in reactors with increased volume. The average specific yield of biohydrogen (per kilogram of initial organic matter (OM)) during recirculation of the methantenk effluent increased by 4% (from 0.1046 to 0.1087 m³/(day 1 kg of OM_in)). In addition, recirculation of the methantenk effluent to the biohydrogen production reactor during two-stage anaerobic bioconversion allowed us to reduce fluctuations in the output of biohydrogen from the reactor. At the same time, there was no methanogenic activity in the anaerobic bioreactor for the production of biohydrogen. The self-stabilizing pH level in the anaerobic bioreactor for producing biohydrogen was less than 4.5 (3.94 without effluent recirculation and 3.88 with recirculation), however, there was no inhibition of hydrogen formation. Thus, the use of recirculation of the methantenk effluent into the anaerobic bioreactor for producing biohydrogen can enhance the efficiency of the two-stage anaerobic bioconversion of organic waste while maintaining the stability of the process.     

Effect of bioaugmentation on hydrogen production from organic fraction of municipal solid waste

In the present study, the effect of bioaugmentation with three bacterial species (i.e. E. coli, Bacillus subtilis and Enterobacter aerogenes) on the hydrogen production from organic fraction of municipal solid waste was evaluated at different bacteria/sludge ratios (0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35 and 0.40). Cumulative hydrogen production, lag phases, and maximum hydrogen production rates were analyzed using modified Gompertz model. The highest cumulative and volumetric hydrogen production of 564.4 ± 10.9 mL and 1.61L_H2/L_substrate respectively was achieved for bioaugmentation with Bacillus subtilis at bacteria/sludge ratio of 0.25. The corresponding highest hydrogen yield was 43.68 mLH₂/gCarbo. For bioaugmentation with E. coli and Enterobacter aerogenes, the maximum cumulative hydrogen production of 423.4 ± 10.6 mL and 486.3 ± 10.6 mL respectively was obtained from bacteria/sludge ratio of 0.20. Corresponding highest hydrogen yields were 32.9 mLH₂/gCarbo and 37.1 mLH₂/gCarbo respectively. Bioaugmentation shortened the lag phases and improved COD removal. Volatile fatty acid generation was also improved with the bioaugmentation.     

Biohydrogen production in anaerobic fluidized bed reactors: Effect of support material and hydraulic retention time

This study evaluated two different support materials (polystyrene and expanded clay) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L⁻¹). The AFBRs contained either polystyrene (R1) or expanded clay (R2) as support materials were inoculated with thermally pre-treated anaerobic sludge and operated at a temperature of 30 °C and a pH of approximately 5.5. The AFBRs were operated with a range of hydraulic retention times (HRTs) between 1 and 8 h. For R1 with an HRT of 2 h, the maximum hydrogen yield (HY) was 1.90 mol H₂ mol⁻¹ glucose, with 0.805 mg of biomass (as total volatile solids, or TVS) attached to each g of polystyrene. For R2 operated at an HRT of 2 h, the maximum HY was 2.59 mol H₂ mol⁻¹ glucose, with 1.100 mg of attached biomass (as TVS) g⁻¹ expanded clay. The highest hydrogen production rates (HPR) were 0.95 and 1.21 L h⁻¹ L⁻¹ for R1 and R2, respectively, using an HRT of 1 h. The H₂ content increased from 16–47% for R1 and from 22–51% for R2. No methane was detected in the biogas produced throughout the period of AFBR operation. These results show that the values of HY, HPR, H₂ content, and g of attached biomass g⁻¹ support material were all higher for AFBRs containing expanded clay than for reactors containing polystyrene.     

Biohydrogen and biomethane production from cassava wastewater in a two-stage anaerobic sequencing batch biofilm reactor

The objective of the present study was to determine the energetic potential from cassava starch wastewater in a two-stage system (BioH₂ + BioCH₄) composed by anaerobic sequencing batch biofilm reactors (AnSBBR). Included in this general objective, the behavior of the methanogenic AnSBBR regarding organic matter removal and biomethane production will be investigated. The acidogenic AnSBBR was operated with organic loading rate (OLR) of 14 gCarb.L⁻¹.d⁻¹, influent concentration of 5 gCarb.L⁻¹ and cycle time of 4 h. The methanogenic AnSBBR was submitted to OLR increase (3.7–12 gCOD.L⁻¹.d⁻¹), provided by arrangements between influent concentration (2.8; 4.0 and 6.0 gCOD.L⁻¹) and cycle time (6; 8 and 12 h). For the evaluated condition, the acidogenic reactor presented productivity of 0.7 LH₂.L⁻¹.d⁻¹ and yield of 1.1 molH₂.kg⁻¹Carb. The methanogenic reactor presented stable methane production (%CH₄ > 78) during the 260-days operating period. The maximum methane productivity (2.71 LCH₄.L⁻¹.d⁻¹) and yield (0.263 LCH₄.g⁻¹COD) were obtained at OLR of 12 gCOD.L⁻¹.d⁻¹ and cycle time of 6 h. The estimated energy production rate in the two-stage system (BioH₂ + BioCH₄) was 105.2 kJ.L⁻¹.d⁻¹.     

Biohydrogen production from food waste in batch and semi-continuous conditions: Evaluation of a two-phase approach with digestate recirculation for pH control

The research investigated the production of Biohythane in a two-phase anaerobic digestion process treating food waste as substrate. Preliminary batch assays were carried out at initial organic loadings of 15, 20, 25 and 30 kg TVS m⁻³, in stirred 1.5-l reactors at 55 °C. The results showed all hydrogen was produced within the first 24 h after feeding and the highest load tested gave the maximum hydrogen production (0.047 m³ H₂ kg⁻¹VS, H₂ 30%). Similar loadings were then tested in a two-phase system. Hydraulic retention times of 3 and 12 days were applied to the first and second reactor respectively. In order to keep the pH at ∼5.5, either supernatant or whole digestate from the methanogenic reactor was recirculated to the first phase. Results showed that hydrogen was produced (0.117 Nm³ kg⁻¹ VS, 47.7%) when recirculating whole digestate with an organic loading rate of 20 kg TVS m⁻³ day⁻¹.     

Hydrogen production via in-line pyrolysis-reforming of organic solid waste enhanced by steel slags

Steel slag derivates prepared from waste steel slag using acid leach method, are employed to promote hydrogen production from organic solid waste by in-line pyrolysis-steam reforming of Chinese medicine residues (CMR). The optimum pyrolysis conditions are determined during the fast pyrolysis experiment of CMR (T_prolysis = 800 °C, F_N2 = 200 mL_STP/min). During in-line pyrolysis-reforming of CMR with steel slag derivates, for example CaO(SS)-50 wt%LR compounds, as reforming catalyst, the hydrogen yield is profoundly increased from 7.57 mmol/g_CMR (pyrolysis operation) to 11.49 mmol/g_CMR, while tar yield has been reduced 30.50%. FeO_x in LR remarkably increases lattice oxygen and adsorption oxygen in NCA-LR or NCA-LR-CaO(SS) compounds, so tar and CO conversion are efficiently improved while coke deposition on catalyst surface is significantly reduced. LR is demonstrated to be able to act as or partially alternate nickel-based catalyst during steam reforming of pyrolysis gas, which would greatly reduce the cost of hydrogen production from OSWs.     

Effect of hydraulic retention time on the hydrogen production in a horizontal and vertical continuous stirred-tank reactor

Hydraulic retention time (HRT) is the main process parameter for biohydrogen production by anaerobic fermentation. This paper investigated the effect of the different HRT on the hydrogen production of the ethanol-type fermentation process in two kinds of CSTR reactors (horizontal continuous stirred-tank reactor and vertical continuous stirred-tank reactor) with molasses as a substrate. Two kinds of CSTR reactors operated with the organic loading rates (OLR) of 12kgCOD/m3•d under the initial HRT of the 8 h condition, and then OLR was adjusted as 6kgCOD/m3•d when the pH drops rapidly. The VCSTR and HCSTR have reached the stable ethanol-type fermentation process within 21 days and 24 days respectively. Among the five HRTs settled in the range of 2–8 h, the maximum hydrogen production rate of 3.7LH₂/Ld and 5.1LH₂/Ld were investigated respectively in the VCSTR and HCSTR. At that time the COD concentration and HRT were 8000 mg/L and 5 h for VCSTR, while 10000 mg/L and 4 h for HCSTR respectively.Through the analysis on the composition of the liquid fermentation product and biomass under the different HRT condition in the two kinds of CSTR, it can found that the ethanol-type fermentation process in the HCSTR is more stable than VCSTR due to enhancing biomass retention of HCSTR at the short HTR.     

Biohydrogen production,sludge granulation,and microbial community in an anaerobic inner cycle biohydrogen production (AICHP) reactor at different hydraulic retention times

This study investigated the continuous biohydrogen production in an anaerobic inner cycle biohydrogen production (AICHP) reactor fed with synthetic molasses wastewater as the model substrate under mesophilic conditions (37 ± 1 °C). The hydraulic retention times (HRTs) were set as 6.12, 4.90, 4.08, 3.50, and 3.06 h. Both maximum hydrogen production rate (HPR) (8.08 ± 0.48 L/L/d) and maximum granule formation were achieved at the HRT of 3.50 h. Acetic acid and butyric acid were the dominant metabolites in all tested HRTs throughout the experiment. Microbial community analysis showed that shortening the HRT promoted hydrogen production. This was mainly achieved by enhancing the growth of acetogenic bacteria in the AICHP reactor, rather than the growth of hydrogen-producing bacteria.     

Hydrogen-rich syngas production from municipal solid waste gasification through the application of central composite design: An optimization study

This study aims to investigate the influence and interaction of experimental parameters on the production of optimum H₂ and other gases (CO, CO₂, and CH₄) from gasification of municipal solid waste (MSW). Response surface method in assistance with the central composite design was employed to design the fifteen experiments to find the effect of three independent variables (i.e., temperature, equivalence ratio and residence time) on the yields of gases, char and tar. The optimum H₂ production of 41.36 mol % (15.963 mol kg-MSW⁻¹) was achieved at the conditions of 757.65 °C, 0.241, and 22.26 min for temperature, ER, and residence time respectively. In terms of syngas properties, the lower heating value and molar ratio (H₂/CO) ranged between 9.33 and 12.48 MJ/Nm³ and 0.45–0.93. The predicted model of statistical analysis indicated a good fit with experimental data. The gasification of MSW utilizing air as a gasifying agent was found to be an effective approach to recover the qualitative and quantitate products (H₂ and total gas yield) from the MSW.     

Supercritical water gasification of organic solid waste: H2 yield and cold gas efficiency optimization considering modeling uncertainties

Supercritical water gasification (SCWG) is one of the typical hydrothermal treatment technologies for organic solid waste. However, the current SCWG optimization methods perform deterministic optimization without considering the uncertainty of the model for calculating the objective function, which leads to low reliability of the optimization results. Therefore, an optimization framework that considers the prediction uncertainties of SCWG data-driven models is proposed to optimize the H₂ yield and cold gas efficiency of organic solid waste SCWG. An ensemble prediction model integrating random forest, gradient boosting regression, and K-nearest neighbor algorithms by the stacking learning method are built to predict SCWG gas yields. The cold gas efficiency prediction model is constructed based on the gas yield prediction models. The SCWG optimization models are constructed by combining the H₂ yield and cold gas efficiency prediction models. The uncertainties in the H₂ yield and cold gas efficiency prediction models are analyzed and integrated into the optimization models. The case studies were conducted to test the proposed framework. The optimization results were verified by the results of similar experimental conditions. It demonstrates that the proposed framework can obtain the robust results of the organic solid waste SCWG optimization, which can provide a reference for SCWG optimization.     

Effects of inoculum and indigenous microflora on hydrogen production from the organic fraction of municipal solid waste

Biological production of hydrogen (H₂) by dark fermentation is an exciting scientific area for the conversion of low-cost residues and waste into biofuel. The main requirement for an efficient H₂ production process is the availability of efficient microbial consortia in which H₂-utilizing and non-H₂-producing bacteria are suppressed. This study was performed to evaluate the H₂ production potentials from the organic fraction of municipal solid waste (OFMSW) with and without addition of inoculum. The results showed that hydrogen productions from OFMSW without addition of inoculum were comparable to those obtained with inoculum but a latency phase of about 6 days occurred. On the contrary, addition of inoculum resulted in higher H₂ production potentials without any latency phase. The use of a properly pre-treated inoculum confirmed to be an interesting and improvable tool to obtain high H₂ yields from organic waste. However the indigenous OFMSW microbiota showed promising hydrogen yields especially toward the development of efficient hydrogen producing microbial inoculants.     

Selective adaptation of an anaerobic microbial community: Biohydrogen production by co-digestion of cheese whey and vegetables fruit waste

The co-digestion process of crude cheese whey (CCW) with fruit vegetable waste (FVW) for biohydrogen production was investigated in this study. Five different C/N ratios (7, 17, 21, 31, and 46) were tested in 2 L batch systems at a pH of 5.5 and 37 °C. The highest specific biohydrogen production rate of 10.68 mmol H₂/Lh and biohydrogen yield of 449.84 mL H₂/g COD were determined at a C/N ratio of 21. A pyrosequencing analysis showed that the main microbial population at the initial stage of the co-digestion consisted of Bifidobacterium, with 85.4% of predominance. Hydrogen producing bacteria such as Klebsiella (9.1%), Lactobacillus (0.97%), Citrobacter (0.21%), Enterobacter (0.27%), and Clostridium (0.18%) were less abundant at this culture period. The microbial population structure was correlated with the lactate, acetate, and butyrate profiles obtained. Results demonstrated that the co-digestion of CCW with FVW improves biohydrogen production due to a better nutrient balance and improvement of the system's buffering capacity.     

A multivariable evaluation of biohydrogen production by solid substrate fermentation of organic municipal wastes in semi-continuous and batch operation

This work focused on the hydrogen production from the organic fraction of municipal solid waste (OFMSW) in solid substrate fermentation (SSF) with a double purpose: (i) to evaluate the effect of the total solids content (20.9 and 35% TS), temperature (35 and 55 °C) and mass retention time (MRT, 21 and 14 d) on semi-continuous fermentation, and (ii) to test the supplementation of OFMSW with nutrient nitrogen in the form of waste activated sludge in batch mini-reactors.