Hydrogen (H2) is considered a clean source of energy and an ideal substitute for fossil fuel owing to its high energy content (122kJ/g), recyclability and non-polluting nature. The conventional ...physicochemical methods for hydrogen production are costly owing to high energy input requirements. Hydrogen production by means of biological processes is considered the most environmental friendly and relatively easy to operate, with successful operation under ambient conditions and promising techniques, and having significant advantages compared with conventional chemical processes. The major bottlenecks in biological processes are the low hydrogen yield and production rates at a large scale. The target is improvement of the biological method for hydrogen production and devising path even better in comparison to the conventional methods. The present review article aims to highlight various techniques such as pretreatment, cell immobilization, sequential fermentation, combined fermentation that have been used in biological processes for enhancing hydrogen production. Future developments on these techniques are also outlined.
The present study investigates the technical possibilities of hydrogen and methane production from palm oil mill effluent (POME). The production was carried out in two stage (thermophilic and ...mesophilic) continuous phase with recirculation of the digestate sludge. The reactors used for the present study, up-flow anaerobic sludge blanket reactor (UASB) and continuous stirred tank reactor (CSTR) were operated under thermophilic and mesophilic conditions, respectively. The UASB reactor was operated at 2 days hydraulic retention time (HRT) and 75 kgCOD m3 d−1 organic loading rate (OLR) for hydrogen production. The effluents from UASB reactor containing mainly with acetate and butyrate were directly fed into CSTR for methane production and 5 days HRT was maintained. Both UASB and CSTR reactors were operated for 120 days continuously, and a stable production of the hydrogen and methane was obtained in the separate reactors. The maximum hydrogen and methane production rate achieved was 1.92 L H2 L−d−1 and 3.2 L CH4 L−1 d−1, respectively. The cumulative hydrogen and methane yields were 215 L H2/kgCOD−1 and 320 L CH4/kgCOD−1, respectively with the total COD removal efficiency of 94%. Thermoanaerobacterium species was dominant in hydrogen reactor, while methane reactor was dominated with Methanobrevibacter sp.
•Assessment of hydrogen production potential and methane production potential in batch experiments.•Evaluation of continuous hydrogen and methane production by digestate sludge recirculation without the addition of pH buffers.•Investigation of the polypropylene for the enhancement of methane production at short HRT in CSTR.
This paper investigates the production of hydrogen (H2) and methane (CH4) from palm oil mill effluent (POME) using an integrated approach of thermophilic continuous stirred tank reactor (CSTR) and ...mesophilic microbial electrolysis cell (MECs). CSTR reactor was operated at pH 5.5, 80 rpm, 2 days HRT, 60 g COD L-1 d-1 organic loading rate (OLR) and 55 °C temperature with the given hydrogen yield of 205 ml H2 gCOD-1 along with acetic, butyric, propionic, and lactic acid as by-products. Continuous, single-chambered MECs fed with dark fermentation effluents were operated at an applied voltage of 0.5 V at 37 °C to obtain methane yield and production rate (MPR) of 290 ml CH4 gCOD-1 and 2700 ml CH4 L-1 at 8 days of hydraulic retention times (HRT). The overall process led to total energy recovery of 92.72% with 91% COD removal efficiency. Microbial community analysis reveals Thermoanerobacterium sp dominated in CSTR whereas exoelectrogens of Methanobacterium formicicum and Methanobacterium beijingense were found to be the chief dominant microbial species on anodic electrode of MECs.
•Sequential hydrogen and methane production were produced from palm oil mill effluent via two-stage bioprocess.•CSTR and MEC were operated at different HRT, OLR, and temperature for optimal gas production.•Microbial Electrolysis Cell reactor showed a maximum methane production rate of 2700 ml CH4 L-1 at HRT of 8 days.•The Anodic electrode of MEC was dominated by Methanobacterium formicicum and Methanobacterium beijingense.
This contribution presents the technical possibilities for continuous hydrogen and methane production using an optimum organic loading rate of palm oil mill effluent in a two-stage reactor at a ...thermophilic temperature of 55 °C. The influence of four organic loading rates, namely, 30, 40, 50, and 60 kg COD/(m3 d) for hydrogen production and 8.3, 10.2, 13.1, 15.8 kg COD/(m3 d) for methane production, were investigated. Hydrogen production was controlled in an up-flow anaerobic sludge blanket reactor at a constant hydraulic retention time of 12 h. The maximum hydrogen content, volumetric hydrogen production rate and hydrogen yield were found to be 45%, 2.5 L H2/d and 33.48 mL H2/g COD, respectively, at the organic loading rate of 50 kg COD/(m3 d). The effluent from the hydrogenogenic reactor was further digested into methane in the continuous stirred tank reactor at a hydraulic retention time of 5 d. The maximum volumetric methane production rate and methane yield were 10.58 L CH4/d. and 0.11 m3 CH4/kg COD, respectively, at an organic loading rate of 13.1 kg COD/(m3 d). A total chemical oxygen demand removal of 91% was achieved in this two-stage process. The scientific contribution of this two-stage technology with an optimized organic loading rate may play a significant role in degrading palm oil mill effluent and developing an energy-efficient strategy for waste management.
•Two stage reactors were developed at 55 °C for the hydrogen and methane generation.•Palm oil mill effluent was used as the effective carbon substrate.•Organic loading rate of 40–60 kg COD/(m3 d) were explored for bioenergy production.•High chemical oxygen demand removal of 91% was achieved at 50 kg COD/(m3 d).
► PEG was used to entrap Clostridium sp. LS2 for hydrogen production from POME. ► Various amount of PEG immobilized cells were tested in UASB reactor for hydrogen production. ► Evaluate the ...efficiency of immobilized UASB reactor for hydrogen production at different HRT. ► Effect of different OLR on hydrogen production in immobilized UASB reactor.
A novel polyethylene glycol (PEG) gel was fabricated and used as a carrier to immobilize Clostridium sp. LS2 for continuous hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. Palm oil mill effluent (POME) was used as the substrate carbon source. The optimal amount of PEG-immobilized cells for anaerobic hydrogen production was 12% (w/v) in the UASB reactor. The UASB reactor containing immobilized cells was operated at varying hydraulic retention times (HRT) that ranged from 24 to 6h at 3.3g chemical oxygen demand (COD)/L/h organic loading rate (OLR), or at OLRs that ranged from 1.6 to 6.6 at 12h HRT. The best volumetric hydrogen production rate of 336mL H2/L/h (or 15.0mmol/L/h) with a hydrogen yield of 0.35L H2/g CODremoved was obtained at a HRT of 12h and an OLR of 5.0g COD/L/h. The average hydrogen content of biogas and COD reduction were 52% and 62%, respectively. The major soluble metabolites during hydrogen fermentation were butyric acid followed by acetic acid. It is concluded that the PEG-immobilized cell system developed in this work has great potential for continuous hydrogen production from real wastewater (POME) using the UASB reactor.
Cell immobilization techniques were adopted to bio-hydrogen production using immobilized anaerobic sludge as the seed culture. Palm oil mill effluent (POME) was used as the substrate carbon source. ...It was found that with a POME concentration of 20g COD/l in the feed, the suspended-cell containing reactor was able to produce hydrogen at an optimal rate of 0.348l H2/(l POME h) at HRT 6h. However, the immobilized-cell containing reactor exhibited a better hydrogen production rate of 0.589l H2/(l POME h), which occurred at HRT 2h. When the immobilized-cell containing reactor was scaled up to 5l, the hydrogen production rate was 0.500–0.588l H2/(l POME h) for HRT 2–10h, but after a thermal treatment (60°C, 1h) the rate increase to 0.632l H2/(l POME h) at HRT 2h. The main soluble metabolites were butyric acid and acetic acid, followed by propionic acid and ethanol.
► PEG was used to entrap Clostridium butyricum EB6 for H2 production from POME. ► Acclimation of immobilized cells improved the H2 production. ► Repeated tests showed the strength of immobilized ...cells for stable and high H2 production. ► Optimal PEG beads dosage and size were tested.
A novel polyethylene glycol (PEG) gel was fabricated and used as a carrier to immobilize Clostridium butyricum EB6 to improve biohydrogen (bio-H2) production from palm oil mill effluent (POME). POME is used as a substrate that can act as a carbon source. The resulting PEG-immobilized cells were found to yield 5.35 LH2/L-POME, and the maximum H2 production rate was 510mL H2/L-POMEh (22.7mmol/Lh). The Monod-type kinetic model was used to describe the effect of substrate (POME) concentration on the H2 production rate. The acclimation of immobilized cells greatly improved H2 production. Batch experiments demonstrated that particle size of PEG-immobilized cells for efficient H2 production 3mm. It is significant that this is the first report on whole-cell immobilization in PEG for H2 production from POME.
Polyethylene glycol (PEG) gel was used to immobilize hydrogen producing Clostridium LS2 bacteria for hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. The UASB reactor with a ...PEG-immobilized cell packing ratio of 10% weight to volume ratio (w/v) was optimal for dark hydrogen production. The performance of the UASB reactor fed with palm oil mill effluent (POME) as a carbon source was examined under various hydraulic retention time (HRT) and POME concentration. The best volumetric hydrogen production rate of 365 mL H2/L/h (or 16.2 mmol/L/h) with a hydrogen yield of 0.38 L H2/g CODadded was obtained at POME concentration of 30 g COD/L and HRT of 16 h. The average hydrogen content of biogas and COD reduction were 68% and 65%, respectively. The primary soluble metabolites were butyric acid and acetic acid with smaller quantities of other volatile fatty acid and alcohols formed during hydrogen fermentation. More importantly, the feasibility of PEG-immobilized cell UASB reactor for the enhancement of the dark-hydrogen production and treatment of wastewater is demonstrated.
► PEG was used to entrap Clostridium LS2 for hydrogen production from POME. ► Effect of packing ratio of PEG immobilized cells was tested in UASB reactor for hydrogen production. ► Evaluate the efficiency of immobilized UASB reactor for hydrogen production at different HRT. ► Effect of different POME concentration on hydrogen production in immobilized UASB reactor.
