Application of polyethylene glycol immobilized Clostridium sp. LS2 for continuous hydrogen production from palm oil mill effluent in upflow anaerobic sludge blanket reactor

► 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.