Relative effectiveness of substrate-inoculum ratio and initial pH on hydrogen production from palm oil mill effluent: Kinetics and statistical optimization

The present study has enabled to establish an appropriate kinetic and operational condition for hydrogen production using ultrasonicated palm oil mill effluent (POME). The kinetic analysis was performed corresponds to cumulative hydrogen (H₂) production by varying substrate-inoculum ratio (COD/VS) from 0.2 to 0.6. The maximum H₂ production potential (P) of 448 mL H₂ with lag-time (ρ) of 8.2 h and H₂ production rate (R_m) of 14.62 mL H₂ h⁻¹ was achieved using the substrate-inoculum ratio of 0.6. However, the R_m of 17.979 mL H₂ h⁻¹ with the ρ of 16.84 h, which is almost double than the substrate-inoculum ratio of 0.6 was observed at a substrate-inoculum ratio of 0.4. Furthermore, response surface methodology (RSM), including experimental design, regression analysis, was successfully applied to achieved optimum substrate-inoculum ratio and initial pH for biological H₂ production from ultrasonicated POME. The maximum yield of 0.416 L H₂/g-COD_removal was observed at the optimum conditions of substrate-inoculum ratio of 0.5 and an initial pH of 5.0. The linear, quadratic and interactive effect of substrate-inoculum ratio and initial pH on H₂ yield were significant.