Enhancing biogas production from water hyacinth juice through biochar addition in an upflow anaerobic sludge blanket reactor

BACKGROUND Recently, sequential crushing and compression pretreatment of water hyacinth has gained attention for its ability in removing recalcitrant lignocellulose components and extract easily from biodegradable water hyacinth juice, facilitating rapid anaerobic digestion (AD) systems. In this work, AD experiments were performed in lab‐scale upflow anaerobic sludge blanket (UASB) reactors using water hyacinth juice as a substrate. To ensure the stability and enhance performance of AD, a batch experiment was performed to select the carbonization temperature and biochar size. The selected biochar was then added to the reactor and compared with the control reactor. The reactors were continuously operated for 65 days to evaluate the treatment efficiency under different hydraulic retention times (HRTs) (4, 2, and 1 days). RESULTS A carbonization temperature of 800 °C with a particle size of 1.58 mm was found to have a higher specific surface area of 519.538 m 2 g −1 and a better pore size of 0.078 mL g −1 . Biogas yields were similar between reactors with and without biochar: 208 ± 86, 370 ± 93, and 393 ± 73 mL g‐ VS −1 (with biochar) and 218 ± 88, 375 ± 107, and 400 ± 74 mL g‐ VS −1 (without biochar) at 4, 2, and 1‐day HRTs, respectively. However, biochar addition improved methane quality, increasing methane content from 78.11% to 81.64% and reducing CO 2 from 21.89% to 18.54%. Both systems achieved high soluble chemical oxygen demand (COD) removal at 1 day HRT: 87.1% with biochar and 85.9% without. CONCLUSION The results indicate that addition of biochar into AD systems offers multiple benefits in enhancing stability and producing a high‐quality methane yield.