Enhancing biogas production from food waste and water hyacinth: effect of co-substrates and inoculum ratios

Waste to energy conversion from invasive species like water hyacinth can lead to multitudinal benefits such as renewable energy generation, fresh water body protection, greenhouse gas emission reduction, and organic fertilizer production. Water hyacinth (WH) is creating havoc by affecting most of the Ethiopian fresh water bodies via disrupting ecosystem processes. Despite the high organic content, biodegradability of WH is a problematic issue due to its high lignin content. In this regard, co-digestion with easily degradable food waste (FW) might alleviate this problem. Hence, this study investigated the effects of feedstock mix ratio and inoculum-feedstock ratio (IFR) on the co-digestion performance of WH (major feedstock) with FW at 37 +/- 1 degrees C, while varying WH to FW ratios (100:0, 50:50, 40:60, and 0:100%), at constant IFR of 1.5, and IFR levels (0.5, 0.75, 1, and 2) at WH: FW mix ratio of 50:50. Biogas production was observed to be the maximum at WH/FW of 40:60% with 495.45 ml/gVSadded and a biodegradability (BD) of 89.3%. While varying IFR biogas production peaked at 462.5 ml/gVSadded with a BD of 86.5% at IFR 2. Moreover, the co-digestion of these substrates resulted in a maximum methane content of 60.06% with a maximum synergy of 122.30%. Additionally, biogas production kinetics were studied using modified Gompertz and first-order kinetic equations with the co-digestion experimental data suggesting a more accurate fit with the modified Gompertz equation. In order to enhance biogas production from WH, the present study findings point out the need to increase the biodegradable fraction in co-digestion as well as IFR. The study's results highlight the potential of co-digestion as an effective approach for enhancing biogas yields from WH to support effective bioenergy recovery approaches.