Interval Analysis of Volatile Solid (VS) and Biochemical Oxygen Demand (BOD) in Batch Anaerobic Fermentation of Selected Agrowaste

Abstract

This study investigated the degradation of volatile solids (VS) and biochemical oxygen demand (BOD) during the anaerobic digestion of selected agro-waste, specifically cassava peels, maize husks, pig slurry, and the composite. The objective was to evaluate the biodegradability of these feedstocks, in line with their potential for biogas production. The Research was conducted at the National Centre for Energy Research and Development (NCERD) laboratory, University of Nigeria Nsukka (UNN). Batch reactors were used to conduct experiments over a period of 45 days. The digesters were operated under controlled conditions, and samples were analyzed at three (3) different points: 24 hours, peak of gas production (day 30), and at the end of the digestion (day 45). The results demonstrated that all the substrates exhibited a reduction in VS and BOD in the course of digestion. However, the most significant reduction in VS and BOD occurred around the peak of gas production. This entails that this period is critical for microbial activity and biogas yield. Corn husks had high initial VS and BOD values of 4.73±0.22 % and 92.80±3.26 mg/L respectively. However, that did not translate to higher biogas production compared with the composite that had initial values of 4.34±0.19 % and 88.00±5.50 mg/L respectively. By the end of the digestion, an average VS reduction of 65% and a BOD reduction of 70% were observed across all substrates, indicating a substantial degradation of organic material. Biogas production was better in the composite (72.580±4.53 %), an indication that higher VS and BOD do not automatically translate to higher gas yield. Thus, factors like multiple substrate interaction affect gas yield and process efficiency.