World Journal of Engineering Research and Technology

*Erewari Ukoha-Onuoha, Ngozi Faith Udenze

ABSTRACT

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 (r=0.88). 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).

[Full Text Article] [Download Certificate] https://doi.org/10.5281/zenodo.20454666