Optimization of Anaerobic Codigestion Process for Biogas Production by Treating Food Waste with Water Hyacinth

Abstract

Sri Lanka faces increasing challenges in waste management and renewable energy due to rising food waste generation and the proliferation of invasive Water Hyacinth (Eichhornia crassipes). This study investigated the optimization of biomethane production through co-digestion of food waste and pretreated water hyacinth, using cow dung as inoculum. Laboratory-scale experiments were conducted in 500mL batch digesters under mesophilic conditions (37◦C) with agitation at 200rpm. Biomethane volume was measured using the water displacement method, with carbon dioxide (CO2) absorbed using 9N sodium hydroxide (NaOH). Four trials were performed: cow dung alone, cow dung with food waste, cow dung with water hyacinth, and cow dung with food waste and water hyacinth. Cumulative biomethane production in the trials was 115, 158, 216, and 240mL, respectively. The highest methane yield of 11.04mL/gVS and maximum production rate of 1.288mL/gVS/h were observed in the co-digestion of all three substrates, with 21.74gVS added. Pretreatment of water hyacinth contributed to increased biomethane production. The Modified Gompertz model closely fitted the experimental data (R2 = 0.8847–0.9952), with minor deviations attributed to substrate heterogeneity and microbial adaptation. These results demonstrate that co-digestion enhances biomethane yield, production rate, process stability, and organic waste conversion efficiency. This study recommends adopting this approach in existing biogas systems to support sustainable energy recovery, effective control of invasive water hyacinth, and improved organic waste management in Sri Lanka.