Performance evaluation of methanogenic digester using kitchen waste for validation of optimized hydrolysis conditions for reduction in ammonia accumulation

Abstract Ammonia accumulation above the inhibitory level is the major cause of failure of anaerobic digesters (AD) treating kitchen waste (KW). In the present investigation a biphasic system (hydrolysis and methanogenesis) was evaluated for validation of previously optimized hydrolysis conditions [pH 7.2–7.5, Aeration 0.19–0.22 vvm (volume of air per unit volume of media per minute), Temperature 44 - 48 °C] for reduction in ammonia accumulation in the methanogenic digester. The pre hydrolyzed KW was fed to methanogenic reactor with the organic loading 1.16 gVS/L - 2.97 gVS/L. Specific biogas and methane yield were 0.589 L biogas/gVS feed and 0.321 L methane/gVS feed under mesophilic condition, and 0.633 L biogas/gVS feed and 0.329 L methane/gVS feed under thermophilic condition, respectively. The ammonia concentration in the methanogenic phase remained below 250 ppm and 550 ppm under mesophilic and thermophilic conditions, respectively, validate the optimized conditions for hydrolysis of KW for reduction in ammonia accumulation in methanogenesis phase. The Microbial diversity analysis of methanogenic phase was carried out to monitor the shifting of microbial population under mesophilic and thermophilic conditions. Results on these aspects have also been presented and discussed in this paper.