Anaerobic digestion of skim latex serum (SLS) for hydrogen and methane production using a two-stage process in a series of up-flow anaerobic sludge blanket (UASB) reactor

A series of up-flow anaerobic sludge blanket (UASB) reactors operated under thermophilic conditions was used to investigate the two-stage anaerobic process for continuous hydrogen and methane production from skim latex serum (SLS). The first reactor for producing hydrogen was operated by feeding 38 g-VS/L-SLS at various hydraulic retention times (HRTs) of 60, 48, 36, and 24 h. The optimum hydrogen production yield of 2.25 ± 0.09 L-H₂/L-SLS was achieved at a 36 h HRT. Meanwhile, the effluents containing mainly with acetate was fed to the second UASB reactor for methane production at 9-day HRT and could be converted to methane with the production yield of 6.41 ± 0.52 L-CH₄/L-SLS. The efficiency of organic matters removal obtained from this two-stage process was 62%. The present study shows high value fuel gases in a form of hydrogen and methane can be potentially generated by using a continuous two-stage anaerobic process, in which available organic matters is simultaneously degraded.     

A pilot study of biohythane production from cornstalk via two-stage anaerobic fermentation

This study aimed to study the feasibility and stability of biohythane production from cornstalk via two-stage anaerobic fermentation without hydrolysis step in a semi-continuous pilot scale system. The present study applied a 1 m³ continuous stirred tank reactor for biohydrogen production and a 0.5 m³ up-flow anaerobic sludge bed for biomethane production. During the entire operation, a hydrogen production yield of 25.02 L/kg TS and hydrogen production rate of 0.46 L/L/d was achieved in first-stage. In addition, a methane yield of 95.38 L/kg TS and methane production rate of 4.06 L/L/d was achieved in second-stage by using the liquid effluent after first-stage. The percentage of hydrogen in the biohythane gas was 18.47% which suitable for vehicle fuel. Moreover, it was feasible to use the solid residue as a growth medium in seedlings to improve energy and carbon recovery. The results suggest that biohythane production from cornstalk could be a promising biofuel avenue.     

Hydrogen and methane production via a two-stage processes (H2-SBR + CH4-UASB) using tequila vinasses

The feasibility of producing hydrogen and methane via a two-stage fermentation of tequila vinasses was evaluated in sequencing batch (SBR) and up-flow anaerobic sludge blanket (UASB) reactors. Different vinasses concentrations ranging from 500 mg COD/L to 16 g COD/L were studied in SBR by using thermally pre-treated anaerobic sludge as inoculum for hydrogen production. Peak volumetric hydrogen production rate and specific hydrogen production were attained as 57.4 ± 4.0 mL H₂/L-h and 918 ± 63 mL H₂/gVSS-d, at the substrate concentration of 16 g COD/L and 6 h of hydraulic retention time (HRT). Increasing substrate concentration has no effect on the specific hydrogen production rate. The fermentation effluent was used for methane production in an UASB reactor. The higher methane composition in the biogas was achieved as 68% at an influent concentration of 1636 mg COD/L. Peak methane volumetric, specific production rates and yield were attained as 11.7 ± 0.7 mL CH₄/L-h, 7.2 ± 0.4 mL CH₄/g COD-h and 257.9 ± 13.8 mL CH₄/g COD at 24 h-HRT and a substrate concentration of 1636 mg COD/L. An overall organic matter removal (SBR + UASB) in this two-stage process of 73–75% was achieved.     

Pre-treatment study on two-stage biohydrogen and biomethane productions in a continuous co-digestion process from a mixture of swine manure and pineapple waste

This study involves continuous co-digestion of swine manure and pineapple waste mixture using two-stage anaerobic reactors and examines hydraulic retention time (HRT) and substrate heat pre-treatment. The maximum hydrogen and methane production rates of 1488.62 and 991.57 mL/L/d, respectively, reached optimal HRTs of 4.5 h in the hydrogen production fermenter (HPF) and 9 d in the methane production fermenter (MPF) using heat pre-treatment. Acetic acid is a dominant volatile fatty acid of the soluble metabolites with values 70%–73% under all the tested conditions and increased values under heat pre-treatment and high HRT. Firmicutes and Euryarchaeota are the main bacteria species detected in HPF and MPF, respectively. The optimal total energy of 196.47 kJ/L/d and chemical oxygen demand (COD) removal efficiency of 90% were obtained by a complete anaerobic co-digestion process at a high substrate concentration of 105 g COD/L and low HRT of 4.5 h. This shows that the two-stage co-digestion process could increase the COD removal efficiency, hydrogen production rate, and net energy gains and produce high quality biogas and significantly reduce fermentation time.     

Optimization of hydrogen production in a granule-based UASB reactor

Hydrogen production from sucrose in a granule-based upflow anaerobic sludge blanket (UASB) reactor was optimized through employing response surface methodology (RSM) with a central composite design in this study. The individual and interactive effects of influent sucrose concentration (S_in) and hydraulic retention time (HRT) on anaerobic hydrogen production were elucidated. Experimental results show that a maximum hydrogen yield of 1.62 mol-H₂/mol-hexose was obtained under the optimum conditions of S_in 14.5 g/L and an HRT 16.4 h. The hydrogen yield was individually dependent on S_in and HRT, while their interactive effect on the hydrogen yield was not significant. Throughout the experiments the hydrogen content fluctuated between 25.9% and 50.0%, but free of methane. Ethanol, acetate and butyrate were the main aqueous products and their yields all correlated well with S_in and HRT, indicating a mixed-type fermentation in this UASB reactor.     

Biohydrogen production with fixed-bed bioreactors

An investigation on anaerobic hydrogen production was conducted in fixed-bed bioreactors containing hydrogen-producing bacteria originated from domestic sewage sludge. Three porous materials, loofah sponge (LS), expanded clay (EC) and activated carbon (AC), were used as the support matrix to allow retention of the hydrogen-producing bacteria within the fixed-bed bioreactors. The carriers were assessed for their effectiveness in biofilm formation and hydrogen production in batch and continuous modes. It was found that LS was inefficient for biomass immobilization, while EC and AC exhibited better biomass yields. The fixed-bed reactors packed with EC or AC (denote as EC or AC reactors) were thus used for continuous hydrogen fermentation at a hydraulic retention time (HRT) of 0.5–5 h. Sucrose was utilized as the major carbon source. With a sucrose concentration of ca. 20 g COD/l in the feed, the EC reactor (workingvolume=300 ml) was able to produce H₂ at an optimal rate of 0.415 l/h/l at HRT=2 h. In contrast, the AC reactor (300 ml in volume) exhibited a better hydrogen production rate of 1.32 l/h/l, which occurred at HRT=1 h. When the AC reactor was scaled up to 3 l, the hydrogen production rate was nearly 0.53–0.68 l/h/l for HRT=1–3 h, but after a short thermal treatment (75°C, 1 h) the rate rose to ca. 1.21 l/h/l at HRT=1 h. The biogas produced with EC and AC reactors typically contained 25–35% of H₂ and the rest was mainly CO₂, while production of methane was negligible (less than 0.1%). During the efficient hydrogen production stage, the major soluble metabolite was butyric acid, followed by propionic acid, acetic acid, and ethanol.     

Bio-hydrogen production during acidogenic fermentation in a multistage stirred tank reactor

The objective of this study was to evaluate the production of hydrogen in a two-stage CSTR system – both reactors having the same volume – and compare its performance with a conventional one-stage process. The lab-scale two-stage and one-stage systems were operated at five pHs and five hydraulic retention time (HRTs). The maximum volumetric hydrogen productivity and yield obtained with the two-stage system were 5.8 mmol L⁻¹ h⁻¹ and 2.7 mol H₂ mol glucose⁻¹, respectively, at an HRT of 12 h and pH 5.5. Overall, the two-stage system showed, at steady state, a better performance that the one-stage system for all the evaluated pHs. However, a comparison between the one-stage system, operating at 6 h of HRT, and the first reactor of the two-stage system at the same HRT did not show any significant difference, highlighting the positive impact of having a two-stage process. The determination of the ratio between the experimental measured H₂ in the gas phase and the theoretical H₂ generated in the liquid phase (discrepancy factor) indicated that an important part of the hydrogen produced in the first reactor was transferred into the second reactor instead of being desorbed in the headspace. Therefore, the improving of hydrogen production in the two-stage system is rather attributed to the increased transfer of hydrogen from liquid to gas than an actual total hydrogen production increase.     

Biological hydrogen production from sweet sorghum syrup by mixed cultures using an anaerobic sequencing batch reactor (ASBR)

Continuous biological hydrogen production from sweet sorghum syrup by mixed cultures was investigated by using anaerobic sequencing batch reactor (ASBR). The ASBR was conducted based on the optimum condition obtained from batch experiment i.e. 25 g/L of total sugar concentration, 1.45 g/L of FeSO₄ and pH of 5.0. Feasibility of continuous hydrogen fermentation in ASBR operation at room temperature (30 ± 3 °C) with different hydraulic retention time (HRT) of 96, 48, 24 and 12 hr and cycle periods consisting of filling (20 min), settling (20 min), and decanting (20 min) phases was analyzed. Results showed that hydrogen content decreased with a reduction in HRT i.e. from 42.93% (96 hr HRT) to 21.06% (12 hr HRT). Decrease in HRT resulted in a decrease of solvents produced which was from 10.77 to 2.67 mg/L for acetone and 78.25 mg/L to zero for butanol at HRT of 96 hr-12 hr, respectively. HRT of 24 hr was the optimum condition for ASBR operation indicated by the maximum hydrogen yield of 0.68 mol H₂/mol hexose. The microbial determination in DGGE analysis indicated that the well-known hydrogen producers Clostridia species were dominant in the reacting step. The presence of Sporolactobacillus sp. which could excrete the bacteriocins causing the adverse effect on hydrogen-producing bacteria might responsible for the low hydrogen content obtained.     

UASFF start-up for biohydrogen and biomethane production from treatment of Palm Oil Mill Effluent

A start-up study was conducted to produce biohydrogen and biomethane from Palm Oil Mill Effluent (POME) using a two-stage up-flow anaerobic sludge fixed-film (UASFF) bioreactor. 100% molasses was used to start the system, and POME was added at 10% increments until it reached 100% after 59 days. During this period of continuous operation, the HRT and temperature were adjusted in order to optimize the condition for biogas production. Hydrogen and methane gas production fluctuated between 53–70% and 90–95%, respectively, in the last four days of operation (days 56–59), with POME percentage being increased from 70% to 100% (30%–0% molasses). Using 100% raw POME led to a total COD removal of 83.70%, average gas production rates of 5.29 L H₂ d⁻¹ (57.11% H₂) and 9.60 L CH₄ d⁻¹ (94.08% CH₄), in their respective units. This output is comparable to, if not better than using 100% molasses as substrate. This work concludes that based on the relative consistency of biogas production on days 56–59, the two-stage UASFF bioreactor operating at a final HRT of 4 h and temperature of 43 °C has taken a period of two months for start-up.     

Direct fermentation of Laminaria japonica for biohydrogen production by anaerobic mixed cultures

A few studies have been made on fermentative hydrogen production from marine algae, despite of their advantages compared with other biomass substrates. In this study, fermentative hydrogen production from Laminaria japonica (one brown algae species) was investigated under mesophilic condition (35 ± 1 °C) without any pretreatment method. A feasibility test was first conducted through a series of batch cultivations, and 0.92 mol H₂/mol hexose_added, or 71.4 ml H₂/g TS of hydrogen yield was achieved at a substrate concentration of 20 g COD/L (based on carbohydrate), initial pH of 7.5, and cultivation pH of 5.5. Continuous operation for a period of 80 days was then carried out using anaerobic sequencing batch reactor (ASBR) with a hydraulic retention time (HRT) of 6 days. After operation for approximately 30 days, a stable hydrogen yield of 0.79 ± 0.03 mol H₂/mol hexose_added was obtained. To optimize bioenergy recovery from L. japonica, an up-flow anaerobic sludge blanket reactor (UASBr) was applied to treat hydrogen fermentation effluent (HFE) for methane production. A maximum methane yield of 309 ± 12 ml CH₄/g COD was achieved during the 90 days operation period, where the organic loading rate (OLR) was 3.5 g COD/L/d.     

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.     

Two-stage anaerobic process for bio-hydrogen and bio-methane combined production from biodegradable solid wastes

A two-stage anaerobic digestion process intended for biohydrogen and bio-methane combined production from organic fraction of municipal solid wastes was investigated. In thermophilic conditions blocking of methanogenesis at the first stage of the anaerobic fermentation was achieved at pH 9.0. Cumulative hydrogen production made 82.5 l/kg volatile solids. Pretreatment of organic fraction of municipal solid wastes and exploitation of mixed cultures of anaerobic thermophilic cellulolytic and saccharolytic bacteria of Clostridia sp resulted in the increase of hydrogen cumulative production up to 104 l/kg volatile solids. Content of methane in biohydrogen didn’t exceed 0.1%. Cumulative bio-methane production made 520 l/kg volatile solids. Methane percentage in produced biogas was 78.6%. Comparison of energy data for two-stage anaerobic digestion with those for solely methane production shows the increase in energy recovery from biodegradable fraction of municipal solid wastes. Results obtained make a foolproof basis for the development of cost-effective technological process providing hydrogen and methane combined production from solid organic wastes. Technology can be implemented at large scale biogas plants improving economical and ecological characteristics of the overall process.     

An approach of auxiliary carbohydrate source on stabilized biohythane production and energy recovery by two-stage anaerobic process from swine manure

In this study, a two-stage biohythane production system was used to treat swine manure to solve the high Chemical Oxygen Demand (COD) concentration and verify the total energy recovery between the two-stage and a traditional single-stage system. Experiments were carried out in single-stage methane production, two-stage biohythane production in long Hydraulic Retention Time (HRT), and short HRT. The COD removal efficiency and energy recovery were finally compared between single-stage (CH₄ fermenter) and two-stage (H₂+ CH₄ fermenter) systems. The results showed that the methane production rate of 53.2 ± 2.7 mL/d.L, the COD removal efficiency of 29.6 ± 5.8%, and total energy recovery of 2.9 ± 0.1 kJ/L.d was obtained in the single-stage of methane production system with HRT 11.08 d, pH 7, and temperature 55 °C, respectively. In the two-stage of hydrogen and methane productions system, the hydrogen production rate of 1.8 ± 0.7 mL/d.L, the methane production rate of 65.7 ± 2.5 mL/d.L, the COD removal rate was 97.8 ± 1.7%, and the total energy recovery of 3.6 ± 0.1 kJ/L.d was obtained and stabilized when the sugary wastewater content gradually reduced to 0%. This study shows that the methane production rate increases 20%, COD removal efficiency increases to 97.8 ± 1.7%, and total energy recovery increases 30%. At the same time, the single-stage (CH₄ fermenter) switched to a two-stage (H₂+ CH₄ fermenter) system. The two-stage anaerobic biohythane production system successfully treated the high organic swine manure and obtained a higher energy recovery against the traditional single-stage of the biomethane production system.     

Hydrogen and methane production in extreme thermophilic conditions in two-stage (upflow anaerobic sludge bed) UASB reactor system

Two-stage hydrogen and methane production in extreme thermophilic (70 °C) conditions was demonstrated for the first time in UASB-reactor system. Inoculum used in hydrogen and methane reactors was granular sludge from mesophilic internal circulation reactor and was first acclimated for extreme thermophilic conditions. In hydrogen reactor, operated with hydraulic retention time (HRT) of 5 h and organic loading rate (OLR) of 25.1 kg COD/m³/d, hydrogen yield was 0.73 mol/mol glucose_added. Methane was produced in second stage from hydrogen reactor effluent. In methane reactor operated with HRT of 13 h and OLR of 7.8 kg COD/m³/d, methane yield was 117.5 ml/g COD_added. These results prove that hydrogen and methane can be produced in extreme thermophilic temperatures, but as batch experiments confirmed, for methane production lower temperature would be more efficient.     

Anaerobic fermentative system based scheme for green energy sustainable houses

The green energy sustainable house based on bio-hydrogen and bio-methane energy technologies proposed in this study employs dark fermentation technology to complete a scheme for green energy sustainable house that includes energy production, storage, distribution control, load applications, recycling, waste treatment, and reuse. In order to resolve the problem of wastewater discharge from hydrogen production in green energy sustainable houses, this study proposes wastewater chemical oxygen demand (COD) treatment research, and suggests the use of two-stage anaerobic treatment to produce two types of bio-energy i.e. hydrogen and methane, while simultaneously reducing COD levels.Methane production employed a condensed molasses fermentation solubles (CMS) and hydrogen fermentation tank effluent as a substrate to test the COD reducing efficiency and overall efficiency of methane production. It was found that if CMS is used during the hydrolysis and acidogenesis stages, the maximum carbohydrate degradation rate will be approximately 70% (F/M ratio of 1.9-2.3), and the COD removal rate will increase from 15 to 20% (F/M ratio of 1.9-2.3) to 68% (F/M ratio of 0.5). This study showed that the total gas (H₂ and CH₄) production yield from effluent of hydrogen fermentation tank (56.2 KJ/mol substrate) is greater than the value for CMS.In this study, a 3.2 m³ anaerobic hydrogen reactor is evaluated to provide a family with 3-4 kW of power. When acclimatization is performed under conditions of 20 g COD/L substrate and hydraulic retention time (HRT) of 8 h, the COD removal rate can reach approximately 50%. If a methane-generating reactor with a 95% COD removal rate is used to degrade effluent from the hydrogen reaction tank, it will be possible to reduce the COD of organic effluent to under 500 mg/L. Since this water quality is not far from that of ordinary untreated household wastewater (approximately 300-500 mg COD/L), the effluent can be discharged into a community sewer system and treated in a community sewage treatment facility.     

Hydrogen and methane production from lipid-extracted microalgal biomass residues

A two-stage process to produce hydrogen and methane from lipid-extracted microalgal biomass residues (LMBRs) was developed. The biogas production and energy efficiency were compared between one- and two-stage processes. The two-stage process generated 46 ± 2.4 mL H₂/g-volatile solid (VS), and 393.6 ± 19.5 mL CH₄/g-VS. The methane yield was 22% higher than the one in the one-stage process. Energy efficiency increased from 51% in the one-stage process to 65% in the two-stage process. Additionally, it was found that repeated batch cultivation was a useful method to cultivate the cultures to improve the methane production rate and reduce the fermentation time. In the repeated batch cultivation, the methane yield slightly decreased if the ammonia levels rose, suggesting that the accumulation of ammonia could affect methane production.     

Simultaneous coproduction of hydrogen and methane from sugary wastewater by an “ACSTRH–UASBMet” system

A two-phase “ACSTR_H–UASB_Met” system has been investigated at the stepwise decreased HRT for the simultaneous production of hydrogen and methane in this study. Hydrogen could be continuously produced from the two-phase hydrogen fermentation of sugary wastewater in ACSTR and effluents from hydrogen fermentation were converted into methane in UASB reactor. At optimum conditions (HRT_H: 5 h, HRT_Met: 15 h), the highest hydrogen production rate of 5.69 (±0.06) mmol L⁻¹ h⁻¹ was obtained from sugary wastewater and methane was continuously produced from effluents of hydrogen fermentation with a production rate of 3.74 (±0.13) mmol L⁻¹ h⁻¹. The total bioenergy recovery by coproduction of hydrogen and methane from sugary wastewater reached 19.37 W and a total of 92.41% of substrate was converted to the biogas (hydrogen and methane) with two-phase anaerobic fermentation.     

Biohydrogen production from soluble condensed molasses fermentation using anaerobic fermentation

Using anaerobic micro-organisms to convert organic waste to produce hydrogen gas gives the benefits of energy recovery and environmental protection. The objective of this study was to develop a biohydrogen production technology from food wastewater focusing on hydrogen production efficiency and micro-flora community at different hydraulic retention times. Soluble condensed molasses fermentation (CMS) was used as the substrate because it is sacchariferous and ideal for hydrogen production. CMS contains nutrient components that are necessary for bacterial growth: microbial protein, amino acids, organic acids, vitamins and coenzymes. The seed sludge was obtained from the waste activated sludge from a municipal sewage treatment plant in Central Taiwan. This seed sludge was rich in Clostridium sp.A CSTR (continuously stirred tank reactor) lab-scale hydrogen fermentor (working volume, 4.0 L) was operated at a hydraulic retention time (HRT) of 3–24 h with an influent CMS concentration of 40 g COD/L. The results showed that the peak hydrogen production rate of 390 mmol H₂/L-d occurred at an organic loading rate (OLR) of 320 g COD/L-d at a HRT of 3 h. The peak hydrogen yield was obtained at an OLR of 80 g COD/L-d at a HRT of 12 h. At HRT 8 h, all hydrogenase mRNA detected were from Clostridium acetobutylicum-like and Clostridium pasteurianum-like hydrogen-producing bacteria by RT-PCR analysis. RNA based hydrogenase gene and 16S rRNA gene analysis suggests that Clostridium exists in the fermentative hydrogen-producing system and might be the dominant hydrogen-producing bacteria at tested HRTs (except 3 h). The hydrogen production feedstock from CMS is lower than that of sucrose and starch because CMS is a waste and has zero cost, requiring no added nutrients. Therefore, producing hydrogen from food wastewater is a more commercially feasible bioprocess.     

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.     

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.