The effects of Trichoderma atroviride pretreatment on the biogas production from anaerobic digestion of water hyacinth

Water hyacinth is an invasive alien plant with several impacts on the environment, economy and society. The plant’s high degree of proliferation makes its mitigation difficult and sometimes complex. However, existing evidence suggests that water hyacinth is a sustainable substrate for biogas production. Using the pretreatment processes for the optimisation conditions for biogas production from water hyacinth, this study analysed the effects of moisture content (60%, 70% and 75%) on Trichoderma atroviride pretreatment of water hyacinth and the impact of the pretreatment on biogas production. Anaerobic digestion of the water hyacinth process was performed at 35°C for 35 days. The modified Gompertz model was used to analyse and predict the appropriate kinetic variables of the digestion process. Biogas yields from untreated, pretreated-60%, pretreated-70% and pretreated-75% were optimal at 135, 210, 217 and 223.4 mL/g of volatile solids (VS). These results suggest the pretreatment of water hyacinth enhanced the degradability of water hyacinth by breaking down the cell wall structure and facilitating its use by microorganisms. Furthermore, the results also confirmed that the higher the moisture content, the easier the biodegradation rate and, consequently, the higher the biogas yield. The model predicted maximum methane production potential ranging from 91.84 to 201 mL/g VS, and the maximum methane yield rate was within 10.12–15.12 mL/day. The lag phase varied between 2.46 and 6.94 days. The percentage error between experimental and model outcomes for untreated, pretreated-60%, pretreated-70% and pretreated-75% are 17.96%, 16.67%, 14.20% and 4.68%, respectively, while the coefficients of determination of the model varied between 0.905 and 0.975, demonstrating significant reliability on attained factors.