Optimization of the operational parameters for mesophilic biohydrogen production from palm oil mill effluent using enriched mixed culture

Improvements in biohydrogen production from palm oil mill effluent (POME) has been achieved by optimizing the physicochemical conditions, using an enriched sludge as inoculum. Enrichment of biohydrogen-producing communities in the sludge was first carried out by heat treatment and acclimatization to POME. Response surface methodology (RSM) was then used for optimizing the operational parameters. The factors investigated were temperature, initial pH, and inoculum concentration. The output responses were evaluated based on the biohydrogen yield (YH2), biohydrogen production rate (RH2), and COD removal efficiency. Microbial analysis of the enriched sludge at 100% POME concentration revealed the abundance of the Firmicutes phylum (98%) among the Bacteria population, with Clostridiaceae as the most abundant family. Archaea were inhibited at both 30% and 100% POME concentration. The optimum operational parameters generated by the RSM model were 34.7 °C, pH 5.81, and inoculum size of 14.22% (v/v), with the following predicted outcomes: YH2 of 42.29 mL H2 gCOD−1, RH2 of 106.09 mL L−1 h−1, and COD removal efficiency of 23.66%. Meanwhile, the experimental data generated were as follows: YH2 of 41.18 mL H2 gCOD−1, RH2 of 109 mL L−1 h−1, and COD removal efficiency of 25.96%. The process reliability was further demonstrated in a larger (2.5 L) continuously stirred-tank reactor, with the maximum biohydrogen yield obtained of 282 mL H2 gCOD−1 and COD removal efficiency of 35%. Butyric and acetic acids were the dominant soluble metabolites produced. These findings suggest that the RSM model generated was successfully used to optimize biohydrogen production from POME using enriched anaerobic digested sludge.