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.
