Sustainable Biogas Production using Food Waste and Animal Excreta

Abstract

The rising fossil fuel dependence and organic waste generation increase the need for sustainable energy such as biogas. In Sri Lanka, food waste and animal manure remain underutilized despite their potential for renewable energy and nutrient recovery. This study aimed to assess the feasibility of biogas production through co-digestion using food waste and animal excreta. Experiments were conducted in four separate trials for both substrates using a 500 mL batch anaerobic digester operated at mesophilic temperature (35–37 °C) with constant agitation at 200 rpm. Biogas volume was quantified by the water displacement method, with 9 N Sodium Hydroxide (NaOH) used as a Carbon Dioxide (CO2) scrubber to allow direct measurement of methane. Substrate quality was analyzed before and after digestion, including Total solids, Volatile solids, pH, COD removal efficiency, and C/N ratio. Methane yields were further modeled using the Modified Gompertz equation to assess kinetic performance. The results revealed that co-digestion significantly enhanced methane generation compared to mono-digestion. Buffalo dung with food waste in 2:1 ratio achieved the highest cumulative methane yield, with experimental values of 8.99 mL/g VS and a Gompertz fit of 9.03 mL/g VS (R2 =0.9893). The higher yield may result from buffalo dung’s stable buffering and rich microbial content. Followed by cow dung with food waste, yielding 7.25 mL/g VS experimentally and 6.85 mL/g VS by Gompertz fit (R2 = 0.9790), dung-only trials produced lower methane volumes. These findings confirm the superior biogas potential and stability of buffalo dung-based co-digestion. Future research is recommended to scale up biogas production systems using the ratio of buffalo dung with food waste in 2:1 and to improve slurry utilization, and expand large-scale applications to reduce food waste and animal manure while addressing local energy demands.