Potential of biogas production from sized cotton yarn waste from textile manufacturing process at Rivatex. Eldoret, Kenya

Abstract

Biogas production is one of the most cost-efficient renewable energy technologies that use biodegradable wastes as feedstock. Sized 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. Nevertheless, CYW could be used as the substrate to generate energy in the form of biogas that can be utilized in other activities like powering textiles production. This research aimed to investigate the potential of biogas production from CYW through the solid anaerobic digestion process. The CYW was collected from Rivatex East Africa Limited, Eldoret, Kenya. The specific objectives were to characterize the substrate for biogas production, determine the optimum ratio of total solids (TS) concentration at different ratios of the substrate on biogas volume yield, and analyse the biogas produced to determine its fractional composition. The experiment was carried out in ten reactors of two-litre capacity. The reactors were loaded with varying concentrations from the highest (50%TS) to the lowest (10%TS). The physicochemical characteristics of materials were determined using standard methods. The biogas produced was measured on daily basis (37 days) using the water displacement method. The analysis of CYW before digestion showed that TS, total volatile solids (TVS), and moisture content (MC) were 93.18 ± 0.21%, 82.48 ± 0.51%, and 6.82 ± 0.48% respectively. Analysis of digested sludge showed that TS, TVS, and MC were 16.78 ± 2.66%, 52.84 ± 2.42%, and 83.58 ± 2.72% respectively. The carbon to nitrogen (C/N) ratio of inoculum was 20.5:1, which is in a suitable range to keep the anaerobic digestion (AD) in a stable condition. However, the CYW had high carbon content; resulting in a C/N ratio of 42.5:1. The reactors presented the different biogas yields with 667.57 ± 4.29 mL per g-TVS, 698.88 ± 1.34 mL per g- TVS, 731.87 ± 2.15 mL per g-TVS, 782.87 ± 3.59 mL per g-TVS, 695.93 ± 3.68 mL per g-TVS, 597.14 ± 3.14 mL per g-TVS, 513.40 ± 2.70 mL per g-TVS, 355.41 ± 3.48 mL per g-TVS, 278.72 ± 4.05 mL per g-TVS, and 203.01 ± 3.34 mL per g-TVS respectively. Reactor four (R4) was the one that presented the highest methane (53.98 ± 0.03%) from biogas produced. The average reduced TS and TVS at the end of digestion were 33.35 ± 3.50% and 36.67 ± 3.87%. Based on the degradation characteristics, R4 had the most significant degradation rates of TS (57.78 ± 0.92%) and TVS (62.96 ± 0.40%) respectively while reactor ten had the lowest one (18.41 ± 0.40% TS and 20.83 ± 0.29% TVS). In conclusion, CYW is a suitable substrate for AD due to its high organic matter. Moreover, biogas yield from CYW has a significant positive relationship with the %TS concentration (p<0.05). The C/N ratio of CYW reported in this study is higher than the optimal value for AD, therefore, the co-digestion of treated CYW with a nitrogen-rich substrate is recommended to help balance the feed nutrients for higher biogas yield. Further studies are recommended to check for ammonium composition in the residues to determine their suitability for application as fertilizer.