Production of biogas from sized cotton yarn wastes

Abstract

Solid waste management is among the environmental challenges facing many industries in the world today. Biogas production is one of the most cost-efficient renewable energy technologies that use biodegradable wastes as feedstock. Furthermore, it is one of the methods for reducing greenhouse gas emission. Cotton Yarn Wastes (CYW) is among the biodegradable wastes that are commonly managed by dumping onto the open land or disposing in sanitary landfills where they undergo anaerobic decomposition. However, CYW could be used as substrate to generate energy in the form of biogas that can be utilized in other activities like powering textiles production. The aim of this study was to investigate the use of CYW as a substrate for biogas production using anaerobic batch reactor. The experiment was carried out in reactors of two-liter capacity. The CYW and inoculum were characterized before and after digestion. The CYW contained 93.18% total solids, 82.48% total volatile solids and 6.82% moisture content while the respective values for digested sludge were 21.61%, 23.61% and 78.38%, respectively. The carbon to nitrogen (C/N) ratio of inoculum was 20.5, which is in the suitable range to keep the anaerobic digestion in a stable condition. However, the CYW had high carbon content; resulting in a C/N ratio of 42.5. The effect of TS concentration at different ratios of CYW on biogas volume produced was investigated. The reactors loading was differentiated using a mixture with concentration corresponding to R 1 (1:1), R 2 (1:1.5), R 3 (1:2), R 4 (1:2.5), R 5 (1:3), R 6 (1:3.5), R 7 (1:4), R 8 (1:5), R 9 (1:6), and R 10 (1:10) on TS content basis i.e. 50%, 40%, 33%, 28%, 25%, 22%, 20%, 18%, 14%, and 10% respectively. The total biogas yield was 6307 mL, 6519 mL, 6711 mL, 7178 mL, 4878 mL, 3868 mL, 3720 mL, 3306 mL, 1164 mL, and 932 mL respectively after 36 days. The results indicated that biogas production increased with increase in TS content. The ratio that provided 28% of TS content had the highest biogas yield. The average reduced TVS at the end of digestion was 88.49%. The results of this test indicated that CYW is a suitable substrate for AD due to its high biodegradability. Therefore, the reactors should run at 28% TS, for maximum biogas generation.