The effect of ISR on OFMSW during acidogenic fermentation for the production of AD precursor: kinetics and synergies

Abstract

Acidogenic fermentation of the organic fraction of municipal solid waste (OFMSW) and its components (food waste, paper waste) was studied in a batch percolator reactor without artificial pH adjustment. The effect of inoculum to substrate ratio on process performance, in terms of pH, hydrolysis and volatile fatty acid (VFA) production, has been investigated. The inoculum to substrate ratio (ISR) was varied from 0 to 0.36 VS/VS and at optimized conditions for fermentation of OFMSW, with ISR 0.23, pH, hydrolysis and acidification yield were 5.5, 625 mg sCOD per g BD VS and 408 mg g⁻¹ BD VS respectively. Due to the uplift of pH from 4 to 5.5 because of addition of ISR, the VFA composition was dominated mostly by butyric, acetic acids and propionic acid. Kinetics regarding rate of hydrolysis and acidification were calculated and reported. A significant synergistic effect was noticed in the acidification and hydrolysis, which were 1.76 and 1.35 fold higher than individual components (paper waste and food waste) of OFMSW, respectively and approximately 70% of biodegradable solid carbon solubilized into the liquid carbon within a short retention time of 78 h.