Systematic Replacement of Freshwater With Aquaculture Effluents for Enhanced Anaerobic Digestion of Food Waste

This research examined the replacement of freshwater in dry anaerobic digestion (AD) of food waste (FW) with brood stock effluent (BSE). A laboratory experiment was conducted in unstirred single phase anaerobic digestion (U-SPAD) system with five different mix-ratios of BSE to tap water (TW): BSE100%, BSE75%:TW25%, BSE50%:TW50%, BSE25%:TW75%, and TW100%. A retention time of 30 days was maintained under mesophilic conditions. Biogas was measured daily, while other parameters including pH, temperature, chemical oxygen demand (COD), and C/N ratio were determined every five (5) days interval. Biogas composition and calorific values were determined at the end of the 30-days. All parameters were measured using standard methods. The biogas yield ranged from 0.38 – 0.52 m3/kg VS while COD reduction ranged from 61 – 68%. Biogas yield correlated strongly with %COD reduction ( . However, ANOVA analysis showed no significant difference in biogas yield among mix-ratios (P = 0.86, F = 0.3234 at p < 0.05). Methane percentage of 64.62 – 85.48% and caloric value of 13.96 – 27.44 MJ/kg were obtained for the various mix-ratios. BSE100% with the highest biogas yield did not produce the most biomethane. BSE75%:TW25% showed the highest methane and calorific value due to lower concentrations of non-combustible gases (nitrogen 4.36% and water vapour 3.64%) compared to BSE100% (nitrogen 6.64 % and water vapour 5.1%). The results demonstrate that BSE can substitute freshwater in AD, reducing fresh water consumption while enhancing methane yield and energy recovery. This aligns with Sustainable Development Goals 6 (Clean Water and Sanitation), 7 (Affordable Energy), and 13 (Climate Action).