Keywords: high–solids anaerobic digestion, distillery grains, stillage, cassava ethanol production, start–up, thermophilic condition, horizontal reactors, environmental technology, ammonia inhibition, methane yield
Feasibility of high solid anaerobic digestion: option for treatment of distillers grains from cassava ethanol production
This research article mainly focused on the feasibility and management of distillers grains produced from ethanol industries using high solid anaerobic digestion systems. A significant barrier for distillers grains in the anaerobic process are its low pH (3.80–4.16) and high C/N ratio (37/1–42/1). According to distillers grains characteristics, the stillage investigated was in dry form (TS 23% to 26%) and contained high organic matter (76% to 83%). The biochemical methane potential (BMP) studies revealed that the distillers grains had a methane potential of 144 NmLCH4/gVS. Four substrate to inoculum ratio (S/I) ratios were studied namely; 0:1, 0.35:1, 1:1 and 7:1 with organic loading rate (OLR) of 2 kgVS/m³.day. The optimum (substrate to inoculums ratio) S/I ratio for high solid anaerobic digestion was found at < 1:1, indicated by reactor performance. Furthermore, four OLR, 2, 3, 3.5, 4 KgVS/m³.day were studied and methane yield during start–up phase were in the range of 0.25–0.28 m³ CH4/kgVSadded for all four loading rates. Ammonia inhibition was not observed in the reactor which indicated that high solid anaerobic digestion for distillers grains is feasible. However, after longer run (60 days), the methane yield decreased to 0.20 m3 CH4/kgVadded due to a lack of nitrogen.