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

Considering the difficulty of digesting coffee husk (CH) and water hyacinth (WH) due to the lignin content, the present study investigated the influence of feedstock mixing ratios on the co-digestion performance of CH and WH with food waste (FW) at 38 ± 1 °C and its kinetics. Food waste was considered as co-substrate due to its ease of digestion. Batch experiments were conducted using CH/WH/FW ratios (100:0:0, 0:100:0, 35:35:30, 30:30:40, 25:25:50, 20:20:60, and 0:0:100 w/w) with total solids (TS) content of about 9.5% (w/v). The results indicated that the addition of FW significantly enhanced WH and CH digestion performance, with the maximum biogas yield of 572.60 \(\pm\) $\pm$ 2.30 mL/gVS, best synergistic effect of 1.5, highest biodegradability of 89.22%, and a biodegradation rate of 57.82% obtained at a mix ratio of 25:25:50, which was improved by 179.71% compared to CH mono-digestion. In addition, the organic conversion efficiency of TS and volatile solids reached 69.86 and 81.48%, respectively. Conversely, CH mono-digestion yielded the lowest biogas yield of 204.71 ± 10.74 mL/g VS, highlighting its unfeasibility. The modified logistic equation showed the best fit to the experimental data. The optimum CH/WH/FW ratio of 25:25:50 demonstrated the highest biogas yield and methane content at 66.30 ± 0.76%.