Comparative study of the effect of chemical treatments on cassava (Manihot utilissima) peels for biogas production

Abstract

A comparative study of biogas production from cassava peels treated with different chemicals namely; potassium hydroxide (KOH, 50% w/v) and locally available potash (“akanwu” 50% w/v) was investigated. The untreated peels formed the control. The fresh cassava peels were degraded aerobically for 4 months before the chemical treatment, waste stabilization and charging of digesters took place. The different variants from the treated peels were charged into 50 L metal prototype biodigesters in the ratio of 2:1 of water to waste. The moisture content of the wastes determined the water to waste ratio. They were charged as; Cassava peels treated with KOH (CP-K), Cassava peels treated with potash (CP-P) and untreated cassava peels (CP-U). They were all subjected to anaerobic digestion under a 30 days retention period and mesophilic temperature range of 25 - 37°C. Results obtained showed that while the untreated cassava peels had cumulative gas yield of 68.7 ± 1.03 L/Total mass of slurry (TMS), the peels treated with potash had highest cumulative gas yield of 124.1 ± 2.67 L/TMS, whereas cassava peels treated with KOH had 111.3 ± 2.44 L/TMS. The flash point for the untreated cassava peels was on the 58th day, while that for the CP-K and CP-P were 10 and 7 days, respectively. The general results showed that the biogas yield from cassava peels can be enhanced by chemical treatment. Results further indicated that locally available potash (“akanwu”) is a better chemical treatment to be employed in the biogas production of cassava peels. Key words: Cassava peels, biogas production, cumulative gas yield, onset of gas flammability, lag period.