Thermophilic hydrogen and methane production from sugarcane stillage in two-stage anaerobic fluidized bed reactors

This study evaluated the feasibility of H₂ and CH₄ production in two-stage thermophilic (55 °C) anaerobic digestion of sugarcane stillage (5,000 to 10,000 mg COD.L⁻¹) using an acidogenic anaerobic fluidized bed reactor (AFBR-A) with a hydraulic retention time (HRT) of 4 h and a methanogenic AFBR (AFBR-S) with HRTs of 24 h–10 h. To compare two-stage digestion with single-stage digestion, a third methanogenic reactor (AFBR-M) with a HRT of 24 h was fed with increasing stillage concentrations (5,000 to 10,000 mg COD.L⁻¹). The AFBR-M produced a methane content of 68.4 ± 7.2%, a maximum yield of 0.30 ± 0.04 L CH₄.g COD⁻¹, a production rate of 3.78 ± 0.40 L CH₄.day⁻¹.L⁻¹ and a COD removal of 73.2 ± 5.0% at an organic loading rate (OLR) of 7.5 kg COD.m⁻³.day⁻¹. In contrast, the two-stage AFBR-A system produced a hydrogen content of 23.9 ± 5.6%, a production rate of 1.30 ± 0.16 L H₂.day⁻¹.L⁻¹ and a yield of 0.34 ± 0.08 mmol H₂.g CODap⁻¹. Additionally, the decrease in the HRT from 18 h to 10 h in the AFBR-S favored a higher methane production, improving the maximum methane content (74.5 ± 6.0%), production rate (5.57 ± 0.38 L CH₄.day⁻¹.L⁻¹) and yield (0.26 ± 0.06 L CH₄.g COD⁻¹) at an OLR of 21.6 kg COD.m⁻³.day⁻¹ (HRT of 10 h) with a total COD removal of 70.1 ± 7.1%. Under the applied COD of 10,000 mg L⁻¹, the two-stage system showed a 52.8% higher energy yield than the single-stage anaerobic digestion system. These results show that, relative to a single-stage system, two-stage anaerobic digestion systems produce more hydrogen and methane while achieving similar treatment efficiencies.     

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.     

Biohythane production from swine manure and pineapple waste in a single-stage two-chamber digester using gel-entrapped anaerobic microorganisms

A mixture of swine manure and pineapple waste was used to check the feasibility of producing biohythane in a newly-developed single-stage anaerobic fermentation system that having immobilized H₂ and CH₄-producing microbes in a two-chamber digester. Tested hydraulic retention times (HRT) were from 96 h to 6 h. HRT 6 h resulted in peak gas production performance with hydrogen production rate 1240 and methane production rate 812 mL/L-d. Besides, the synergistic function of generation and consumption of volatile fatty acids in this hybrid biosystem had a significant impact on biohythane composition with acetate and butyrate being the dominant liquid metabolites. Chemical oxygen demand and ammonium removal efficiencies were 52.4 and 78.8%, respectively during steady-state conditions. Based on the experimental findings, prospects for field applications of single-stage biohythane fermentation were suggested.     

Biohythane production in two-stage anaerobic digestion system

Hydrogen (H₂) and methane (CH₄) are the potential alternative energy carriers with autonomous extensive and viable importance. These fuels could complement the advantages, and discard the disadvantages of each other, if produced simultaneously. Considering their complementary properties, co-production of a mixture of H₂ and CH₄ in the form of biohythane in two-stage anaerobic digestion (AD) process is gaining more interest than their individual production. Biohythane is a better transportation fuel than compressed natural gas (CNG) in terms of high range of flammability, reduced ignition temperature as well as time, without nitrous oxide (NOx) emissions, improved engine performance without specific modification, etc. Other than production of biohythane, performing two-stage AD is advantageous over one-stage AD due to short HRT, high energy recovery, high COD removal, higher H₂ and CH₄ yields, and reduced carbon dioxide (CO₂) in biogas. For improved biohythane production, various aspects of two-stage AD need to be emphasized. Keeping the facts in mind, the process of two-stage AD along with microbial diversity in comparison to one-stage AD has been discussed in the previous sections of this review. For large scale commercial production, and utilization of biohythane in automobile sector, its execution needs evaluation of process parameters, and problems associated with two-stage AD. Hence, the later part of this review describes the production process of biohythane, concerned microbial diversity, operational process parameters, major challenges and their solutions, applications, and economic evaluation for enhanced production of biohythane.     

Pilot-scale of biohythane production from palm oil mill effluent by two-stage thermophilic anaerobic fermentation

The pilot-scale of two-stage thermophilic (55 °C) for biohythane production from palm oil mill effluent (POME) was operated at hydraulic retention time (HRT) of 2 days and organic loading rate (OLR) of 27.5 gCOD/L⋅d) for first stage and HRT of 10 days and OLR of 5.5 gCOD/L⋅d for second stage. Biohythane production rate was 1.93 L-gas/L⋅d with biogas containing 11% H₂, 37% CO₂, and 52% CH₄. Recirculation of methane effluent mixed with POME at a ratio of 1:1 can control pH in the first stage at an optimal range of 5.0–6.5. Microbial community in hydrogen stage dominated by Thermoanaerobacterium sp., while methane stage dominated by Methanosarcina sp. The H₂/CH₄ ratio of biohythane was 0.13–0.18 which suitable for vehicle fuel. Biohythane production from POME could be promising cleaner biofuel with flexible and controllable H₂/CH₄ ratio.     

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.     

Effect of pH shock on single-stage biohythane production using gel-entrapped anaerobic microorganisms

A novel single-reactor system having entrapped anaerobic microorganisms has been developed to co-produce H₂ and CH₄. pH is one of the key operating and environmental parameters affecting the performance of a bio-system. This work aimed to investigate the pH shock effects on the novel biohythane system. The experiments were suddenly changing the original cultivation pH value of 6 into 4, 5, 7 or 8 for 4 h. The results indicate that a short pH shock could be used to regulate H₂/CH₄ composition without notably affecting biogas yield and chemical oxygen demand (COD) removal. Peak biohythane production was obtained after the pH shock to 8, having H₂/CH₄ yields of 11.5 ± 1.6/44.8 ± 3.1 mL/g COD. During pseudo steady-state conditions of effective cultivation periods, the values of H₂ content in biohythane and COD removal efficiency were in ranges of 20–39% and 71–79%, respectively. The significances and applications of the experimental results have been discussed. The novelty of this work is elucidating a less-discussed field-operation problem of pH perturbances for a newly-developed biohythane system.     

Anaerobic hydrogen and methane production from low-strength beverage wastewater

In this study, the low-strength effluent from an equalization tank of the wastewater treatment plant in a beverage factory was used for the production of hydrogen and methane. The COD concentration of this low-strength wastewater was 2.9 ± 2.0 g COD/L. In a two-phase anaerobic fermentation system, the hydrogen-producing bioreactor was operated at HRT 8 h, while the methane-producing reactor operated at HRT 24 h. The maximum MPR, methane yield (MY), methane content and COD removal were 72 ± 31 mL/L-d, 58 ± 12 mL/g COD, 92 ± 2% and 78%, respectively. Energy efficiency in this study was calculated as follows, the maximum heating value was 2.2 × 10⁸ kcal/y. The annual carbon-emission reduction was 8.8 × 10⁴ kg CO₂/y, 5.2 × 10⁴ kg CO₂/y, 7.2 × 10⁴ kg CO₂/y when energy-equivalent coal, natural gas or fuel was used, respectively.     

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.     

Effect of pH control on biohythane production and microbial structure in an innovative multistage anaerobic hythane reactor (MAHR)

An innovative multistage anaerobic hythane reactor (MAHR) which combines an internal biofilm (M_H) and an external up-flow sludge blanket (M_M) was proposed to produce biohythane from wastewater. The effect of pH on its biohythane production and microbial diversity was performed. Results showed that the maximum hydrogen production rate (4.900 L/L/d) was achieved at a pH of 6.0, in comparison to a maximum methane production rate of 10.271 L/L/d at a pH of 6.5. In addition, a suitable hythane (H₂/(H₂+CH₄) of 16.06%) production can be achieved in M_H after the initial pH was adjusted from 7.0 to 6.5, and a relatively high methane yield (271.34 mL CH₄/gCOD) was obtained in M_M. Illumina Miseq sequencing results revealed that decreasing pH led to an increase of the acidogenesis families (Eubacteriaceae, Ruminococcaceae) in M_H and an increase of hydrogenotrophic methanogens (Methanobacteriaceae) in M_M. The Methanosaetaceae gradually occupied a major portion after a long period of recovery. This work demonstrated the unique advantages of MAHR for the biohythane production under optimal pH conditions.     

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.     

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.     

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.     

Enhanced biogas production from anaerobic co-digestion of municipal wastewater treatment sludge and fat,oil and grease (FOG) by a modified two-stage thermophilic digester system with selected thermo-chemical pre-treatment

Anaerobic co-digestions with fat, oil and grease (FOG) were investigated in two-stage thermophilic (55 °C) semi-continuous flow co-digestion systems. One two-stage co-digestion system (System I) was modified to incorporate a thermo-chemical pre-treatment of pH = 10 at 55 °C, which was the best pre-treatment condition for FOG co-digestion identified during laboratory-scale biochemical methane potential (BMP) testing. The other two-stage co-digestion system (System II) was operated without a pre-treatment process. The anaerobic digester of each digestion system had a hydraulic retention time (HRT) of 24 days. An organic loading rate (OLR) of 1.83 ± 0.09 g TVS/L·d was applied to each digestion system. It was found that System I effectively enhanced biogas production as the thermo-chemical pre-treatment improved the substrate hydrolysis including increased COD solubilization and VFA concentrations. Overall, the modified System I yielded a 25.14 ± 2.14 L/d biogas production rate, which was substantially higher than the 18.73 ± 1.11 L/d obtained in the System II.     

Trace metals supplementation enhanced microbiota and biohythane production by two-stage thermophilic fermentation

The effect of trace metals supplementation into palm oil mill effluent on biohythane production and responsible microbial communities in thermophilic two-stage anaerobic fermentation was investigated. High biohythane yields were linked to Ni/Co/Fe supplementation (10, 6 and 20 mg L⁻¹, respectively) with maximum H₂ and CH₄ yields of 139 mL H₂ gVS⁻¹ and 454 mL CH₄ gVS⁻¹, respectively. The Ni/Co/Fe supplementation resulted in higher numbers of Bacillus sp., Clostridium sp. and Thermoanaerobacterium sp. together with increasing hydrogenase expression level leading to increasing hydrogen yields of 90.4%. The numbers of Methanosarcina, Methanomassiliicoccus, and Methanoculleus were enhanced by Ni/Co/Fe addition, accompanied by 21.7% higher methane yields. No correlation between methyl coenzyme-M reductase expression level and methane yields was observed. The Ni/Co/Fe supplementation improved gas production in the two-stage biohythane process via enhancing a number of viable hydrogen-producing bacteria together with hydrogenase activity in H₂ stage and enhancing number methanogens in the CH₄ stage.     

Two-stage UASB reactor converting coffee drink manufacturing wastewater to hydrogen and methane

In this study, the feasibility of a continuous two-stage up-flow anaerobic sludge blanket (UASB) reactor system, consisted of thermophilic (55 °C) dark fermentative H₂ production and mesophilic (35 °C) CH₄ production from coffee drink manufacturing wastewater (CDMW), was tested. A recently proposed operational strategy was used to overcome a major drawback of the long start-up period of the UASB reactor. Firstly, a completely stirred tank reactor (CSTR) was operated for 8 days to prepare seeding. The seed was then directly transferred to the UASB reactor. Microbial aggregation took place in the initial period, and the floc size was gradually increased over time. In UASB reactor, the maximum H₂ yield of 2.57 mol H₂/mol hexose_added and a stable H₂ production rate of 4.24 L H₂/L/h were observed at a hydraulic retention time (HRT) of 6 h and substrate concentration of 20 g Carbo. COD/L. In this novel method using CDMW, thermophilic H₂-producing granules with an average particle size of 1.3 mm was successfully developed after 100 days. The more bioenergy recovery was attempted in a post-treatment process using a mesophilic UASB reactor for CH₄ production from the H₂ fermented effluent. The maximum CH₄ yield of 325 mL of CH₄/g COD was achieved with removing 93% of the COD at an organic loading rate of 3.5 g COD/L/d. The developed two-stage UASB reactor system achieved biogas conversion by 88.2% (H₂ 15.2% and CH₄ 73%) and COD removal by 98%.     

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.     

Improvement of biohythane production from Chlorella sp. TISTR 8411 biomass by co-digestion with organic wastes in a two-stage fermentation

The suitability of molasses, Napier grass (Pennisetum purpureum), empty fruit bunches (EFB), palm oil mill effluent (POME), and glycerol waste as a co-substrate with Chlorella sp. TISTR 8411 biomass for biohythane production was investigated. Mono-digestion of Chlorella biomass had hydrogen and methane yield of 23–35 and 164–177 mL gVS⁻¹, respectively. Co-digestion of Chlorella biomass with 2–6% TS of organic wastes was optimized for biohythane production with hydrogen and methane yield of 17–75 and 214–577 mL gVS⁻¹, respectively. The hydrogen and methane yield from co-digestion of Chlorella biomass with molasses, POME, and glycerol waste was increased by 8–100% and 80–264%, respectively. The biohythane production of co-digestion of Chlorella was 6–11 L L-mixed waste⁻¹ with an optimal C/N ratio range of 19–41 and H₂/CH₄ ratio range of 0.06–0.3. Co-digestion of Chlorella biomass was significantly improved biohythane production in term of yield, production rate, and kinetics.     

Optimizing energy harvest in wastewater treatment by combining anaerobic hydrogen producing biofermentor (HPB) and microbial fuel cell (MFC)

This study focused on the optimization of energy harvest from wastewater treatment by integrating two novel biotechnologies: anaerobic hydrogen production and microbial fuel cell (MFC). The simultaneous production of hydrogen and electricity from wastewater was examined at continuous flow at different organic loading rates (OLR) by changing chemical oxygen demand (COD) and hydraulic retention time (HRT). The experimental results showed that the specific hydrogen yield (SHY, mole H₂/mole glucose) increased with the decrease in OLR, and reached at the maximum value of 2.72 mol H₂/mole glucose at the lowest OLR of 4 g/L.d. The effluent from hydrogen producing biofermentor (HPB) was fed to a single chamber MFC (SCMFC), obtaining the highest power density and coulombic efficiency (CE) of 4200 mW/m³ and 5.3%, respectively. The energy conversion efficiency (ECE) increased with OLR and reached the peak value of 4.24% at the OLR of 2.35 g/L.d, but decreased with higher OLR. It was demonstrated that the combination of HPB and MFC improved the ECE and COD removal with the maximum total ECE of 29% and COD removal of 71%. The kinetic analysis was conducted for the HPB-MFC hybrid system. The maximum hydrogen production was projected to be 2.85 mol H₂/mole glucose. The maximum energy recovery and COD removal efficiency from MFC were projected to be 559 J/L and 97%, respectively.     

Effect of hydraulic retention time on hydrogen production and chemical oxygen demand removal from tapioca wastewater using anaerobic mixed cultures in anaerobic baffled reactor (ABR)

This study evaluated hydrogen production and chemical oxygen demand removal (COD removal) from tapioca wastewater using anaerobic mixed cultures in anaerobic baffled reactor (ABR). The ABR was conducted based on the optimum condition obtained from the batch experiment, i.e. 2.25 g/L of FeSO₄ and initial pH of 9.0. The effects of the varying hydraulic retention times (HRT: 24, 18, 12, 6 and 3 h) on hydrogen production and COD removal in a continuous ABR were operated at room temperature (32.3 ± 1.5 °C). Hydrogen production rate (HPR) increased with a reduction in HRT i.e. from 164.45 ± 4.14 mL H₂/L.d (24 h HRT) to 883.19 ± 7.89 mL H₂/L.d (6 h HRT) then decreased to 748.54 ± 13.84 mL H₂/L.d (3 h HRT). COD removal increased with reduction in HRT i.e. from 14.02 ± 0.58% (24 h HRT) to 29.30 ± 0.84% (6 h HRT) then decreased to 21.97 ± 0.94% (3 h HRT). HRT of 6 h was the optimum condition for ABR operation as indicated.