Assessment of Inoculum to Substrate Ratio to Recover Energy from Cassava Wastes Through Anaerobic Digestion

Abstract

The proliferation of cassava agro-food industries leads serious environmental problems due to the pollutants organic wastes discharge into the environment and heavy pressure put on forest resources to meet their internal energy needs. Biogas generated by anaerobic digestion is a versatile renewable energy vector regarding to the methane content which can be used to replace firewood and provide cassava factories with cost-effective energy. Cassava wastes show high biodegradables carbohydrates content against low nitrogen content. Due to the sugars content, cassava waste failed rapidly in inhibition during anaerobic digestion process. This paper focused on optimization of cassava wastes anaerobic digestion by using some chemical and adjusting the inoculum to substrate (I/S) ratio. The I/S = 1 is optimal to reach the maximal methane yield from cassava wastes. The biochemical methanogenic potential (BMP) showed 368 ± 26 mL/gVS; 156 ± 63 mL/gVS; 309 ± 75 mL/gVS respectively for untreated cassava wastewater (CWW), cassava peels treated with sodium bicarbonate (CP-Na) and cassava peels treated with potash locally (CP-P) called «akanwu». Untreated cassava peels (U-CP) yielded biogas with no methane content. The average methane content of the vial was at 71% (v/V) after 15 days of solid retention time (SRT) of CWW, 47% (v/V) and 58% (v/V) respectively for CP-Na and CP-P after 7 days of residence time.