Enhancing Biodegradability of Coffee Husk and Water Hyacinth using Food Waste: Synergistic and Kinetic Evaluation under Co-digestion

Abstract

Abstract Coffee husk (CH) and water hyacinth (WH) are seen as environmental challenges causing eutrophication of water streams and infestation of water bodies. These biomass resources, available in plenty with high organic content can be considered for anaerobic digestion. However, their high lignin content poses a challenge to their biodegradability in which case co-digestion with easily degradable food waste (FW) could alleviate this problem. Thus, the synergistic effect with co-digestion of CH and WH employing increasing FW levels on biogas yield, biodegradability (BDfpc), and biodegradation rate (ηBD) were investigated in this work. Experimental studies were conducted with a varied mixtures of CH/WH/FW (100:0:0, 0:100:0, 35:35:30, 30:30:40, 25:25:50, 20:20:60 and 0:0:100) at constant temperature (38 ± 1°C). The results indicated that addition of FW significantly enhanced WH and CH digestion performance, with the maximum biogas yield of 572.60 ml/gVS, highest BDfpc of 89.22% and ηBD of 57.82% obtained at a mix ratio of 25:25:50, which was improved by 194.98% compared to CH mono-digestion. The co-digestion tests exhibited strong synergy due to their nutritional balance and other interactive effects promoting stability. Maximum synergy was 1.72 for a mix of 20:20:60. The modified Gompertz, logistic, and first-order kinetic models were used to simulate the experimental data to portray the biodegradation and kinetics involved. The modified logistic equation was seen to be the best fit to elucidate biogas production. The current findings highlighted the importance of increasing the easily biodegradable waste fractions in the co-digestion of lignocellulosic biomass for enhanced biodegradability.