Biochemical Methane Potential Assay Using Single Versus Dual Sludge Inocula and Gap in Energy Recovery from Napier Grass Digestion

Abstract

Potential energy recovery from Napier grass biomass was evaluated in batch mode and later compared with different digestion techniques, i.e., theoretical calculation and anaerobic digester operations. In the first part, different anaerobic digester sludges from pig farm, palm oil mill, and concentrated rubber latex factory, designated as PIG, PALM, and RUB in order, were evaluated for their ability as inoculant for biochemical methane potential (BMP) study. Using the first-order and Gompertz models, PIG and RUB were found to possess highest hydrolysis and methanogenesis activities, respectively. Prior to full BMP test on real biomass, suitable inoculum to substrate ratio (ISR) was identified, where ISR ≥1 g VSinoculum per g VSsubstrate was found statistically equivalent for the Napier grass substrate. Results from a series of BMP assays revealed a far more superior digestibility performance of the dual sludge inoculum over the individual PIG and RUB at 32% and 49%, respectively. The protocol proposed in this study could be used as an evaluation and selection guideline for BMP inoculum. In the second part, these BMP results were compared and contrasted with the theoretical methane potential and methane yields from wet and dry Napier grass digester operations in reference to the recoverable energy of this biomass. Gap between different methods suggests rooms for improvement and utilization of the residue.