Enhancement of biogas production and nutrient recovery from water hyacinth juice in an upflow anaerobic sludge blanket reactor

Abstract Water hyacinth is an invasive aquatic plant that poses significant environmental and water management challenges. Converting this abundant biomass into bioenergy through anaerobic digestion offers a sustainable solution; however, limited studies have evaluated its performance in liquid form under short hydraulic retention times (HRTs), particularly with different inoculum sources. This study examined energy production and nutrient recovery from water hyacinth juice through anaerobic digestion, comparing activated sludge and digested cow dung as inocula. Experiments were carried out in a lab-scale upflow anaerobic sludge blanket (UASB) reactor at HRTs of 6, 4, and 2 days under mesophilic conditions (37°C) and near-neutral pH. Performance was evaluated by measuring biogas and methane production, solids content, nutrient levels, and chemical oxygen demand (COD). Activated sludge produced a higher biogas yield (0.278 L/g VS) compared to digested cow dung (0.109 L/g VS), with COD reductions from approximately 3377 mg/L to 1195 mg/L and 1369 mg/L, respectively. Methane content was similar, at 73.4% and 72.0%. Nitrate levels declined, while phosphate levels increased in both systems. These results show that water hyacinth juice can be effectively treated in a UASB reactor at short HRTs, producing measurable biogas and nutrient changes, with activated sludge offering better performance.