Biohydrogen production from palm oil mill effluent using polyethylene glycol immobilized cells in upflow anaerobic sludge blanket reactor

The demand for improvement of the hydrogen production by dark hydrogen fermentation is increasing. Recently, a number of cell-immobilization systems were used to improve dark hydrogen production. The main objective of this research was to examine the polyethylene glycol immobilized cells system in enhancing hydrogen production and treatment of palm oil mill effluent (POME). During this research five experiments were performed. In the first experiment, PEG gel was fabricated and used as a carrier to immobilize Clostridium sp. for biohydrogen production using POME. POME was diluted and used as a substrate. The resulting PEG-immobilized cells were found to yield 5.35 L H /L-POME, and the maximum hydrogen production rate was 0.5 L H 2 2 /L-POME/h (22.7 mmol/L h). The Monod-type kinetic model was used to describe the effect of substrate (POME) concentration on the hydrogen production rate. Furthermore, PEG- immobilized cell was examined for H production in comparison to suspended cell reactor. The suspended-cell containing reactor was able to produce hydrogen at an optimal rate of 0.348 L H /L-POME/h at HRT 6 h. However, the immobilized-cell containing reactor exhibited better hydrogen production rate of 0.589 LH 2 2 / L-POME/h which occurred at HRT 2 h. When the immobilized-cell containing reactor was scaled up to 5 L, the hydrogen production rate was 0.553–0.589 L H / L-POME/h. Another study addressed the application of a PEG-immobilized upflow anaerobic sludge blanket (UASB) reactor using Clostridium sp. for enhancing continuous hydrogen production from POME. The UASB reactor containing immobilized cells was operated at varying hydraulic retention times (HRT) that ranged from 24 to 6 h at 3.3 g chemical oxygen demand (COD)/L/h organic loading rate (OLR), or at OLRs that ranged from 1.6 to 6.6 at 12 h HRT. The maximum volumetric hydrogen production rate of 0.336 LH 2 /L/h (15.0 mmol/L/h) with a hydrogen yield of 0.35 LH 2 /g COD was obtained at a HRT of 12 h and an OLR of 5.0 g COD/L/h. The effect of immobilized cell packing ratio, HRT and POME concentration on continuous hydrogen production and treatment efficiency of palm oil mill effluent was studied. 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 highest volumetric hydrogen production rate of 0.365 L H removed /L/h (16.2 mmol/L/h) with a hydrogen yield of 0.38 LH 2 /g COD 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 66%, respectively. In the final study, optimization of the hydrogen production capability of the immobilized cells, including PEG concentration, cell loading, curing times as well as effects of temperature and different inorganic components concentrations on hydrogen production rate were studied. Result showed that with an optimal PEG concentration (10 % w/v), cell loading (2.4 g dry wt.), curing time (80 min) and inorganic components (NiCl 2 1 mg/L , FeCl 2 300 mg/L removed and MgSO 100 mg/L), attaining an excellent hydrogen production rate of 7.3 L/L-POME/d and a hydrogen yield of 0.31 L H /g COD in continuous operatio