Anaerobic Co-Digestion of Kitchen and Animal Wastes at Varying Mixing Ratios

Abstract

The treatments of potato:chicken dung (POP:CHD), yam peel:cow dung (YP:CD) and unripe plantain peel:cow dung (PP:CD) wastes by anaerobic co-digestion were studied. This study was carried out to examine the attractiveness of these wastes at various mixing ratios as a source of biogas production. A hydraulic retention time (HRT) of 30 days was applied for the digestion process. Biogas production was collected by downward displacement of water. The maximum volume of biogas production from POP: CHD co-digestion was obtained as 5,705 ml at 20% POP:CHD mixing ratio. The maximum volume of biogas production from YP:CD and PP:CD co-digestions were obtained as 1,375 and 1,305 ml at the mixing ratio of 20:80. The parameters analyzed (pH, temperature, total suspended solids (TSS), carbon oxygen demand (COD), etc.) fell within the prescription limits of WHO (World Health Organization). The initial COD values for all the varying mixing ratios ranged between 77.33 - 226.67 mg/l while the COD values at the end of the digestion process ranged between 168 – 280 mg/l respectively. The initial TSS values for all the varying mixing ratios ranged between 10.85 - 37.55 mg/l while the TSS values at the end of the digestion process ranged between 11.15 – 28.80 mg/l respectively. The WHO standard values for COD and TSS are 200 mg/l and 30 mg/l respectively. The kinetics of anaerobic digestion of the wastewater was described by first-order kinetic model. This study showed that biogas can be successfully produced from POP:CHD, YP:CD and PP:CD co-digestions. The slurries obtained can be applied as manure because their improved flow properties would enable the digestate to penetrate faster in the soil.