Two-stage (liquid-solid) anaerobic mono-digestion of ammonia-rich chicken manure at low-temperature: Operational strategy and techno-economic assessment

This study investigated mono-digestion of ammonia-rich chicken manure (CM) in a high-solids anaerobic-digester (HSAD) at low-temperature (20±1°C) adopting the recirculation-percolation mode of operation using liquid-inoculum. HSAD was operated for about 282 days in batch-runs under different organic loading rates (4.3-8.7 gVS/L.d), total solids (65-70%) and total kjeldahl nitrogen (TKN) (23.3- 32.8 g/L) concentrations. It was noted that acclimation of the liquid inoculum to a high concentration of TKN (6.9 g/L) facilitated CM digestion, thereby reducing the start-up phase. The maximum cumulative biogas production rate and specific methane yield were found to be 20 L/d and 0.80±0.12 LCH₄g/VS_fed, respectively with a methane content over 60% without any signs of inhibition. Operating HSAD at low temperature prevented the accumulation of free-ammonia, which is toxic to methanogens. A techno-economic analysis was also conducted as part of this study to determine the profitability of the system and a 9-year tentative payback period was estimated.