Utilisation of raw palm oil mill effluent (POME) as a renewable substrate for fermentative H2 production: Optimisation using statistical approach

Fermentative H-2 production was studied using raw POME as the substrate with heat-shock pre-treated POME anaerobic sludge acted as the inoculum. The effect of crucial operating variables (initial pH of medium, incubation temperature, and inoculum size) on H-2 production was studied using Box-Behnken Design. A second-order polynomial regression model was generated to evaluate H-2 production trend under conditions tested. The model analysis revealed the high significance of linear effects of initial pH, incubation temperature, and inoculum size (P < 0.01) towards H-2 production. Similar results indicated that the interaction effect between initial pH and inoculum size, and interaction effect between incubation temperature and inoculum size were highly significant (P < 0.01). The regression model suggested that the optimum conditions were set to a pH value, incubation temperature and inoculum size of 6.4, 58.0 degrees C and 8.0% v/v, respectively. In order to validate the optimum conditions determined by the model, heat-shock pre-treated POME anaerobic sludge was incubated with raw POME under optimum conditions. Validation experiment showed that a cumulative H-2 volume of 239.0 mL was produced. Microbial community analysis of inoculum showed that mixed consortia between Clostridium sp. and other obligate anaerobic non-spore forming bacteria, mostly belonging to the Firmicutes and Bacteroidetes phyla were identified as the major H-2-producers and were hugely responsible towards fermentative H-2 production.