Biogas production from piggery waste at abattoirs

Abstract

Growth in the pig value chain is associated with a proportionate increase in the energy required and waste generated at abattoirs. At Ugandan abattoirs, there is already a deficit in the energy required for mandatory electrical appliances as well as utilization of conventional heating methods. This trend can be reversed through successful implementation of waste to energy conversion technologies. It is against this background that this study sought to determine the techno-economic viability of waste to energy conversion from piggery abattoirs in Uganda using Wambizzi abattoir as a case study. Energy requirements and waste generated at the abattoir were monitored for three weeks. Pig manure (PM) and gastrointestinal tract contents (GC) samples were characterized and five treatments in duplicate were set up in batch experiments for production of biogas in the ratios of 1:0 (S1), 1:1 (S2), 1:2 (S3),1:3 (S4) and, 0:1 (S5) for PM: GC respectively. The quantity and quality of biogas were determined after the retention time of 30 days. Based on the results from experiments and data collected from the abattoir, an appropriate biogas digester was designed for the abattoir, its economic performance and carbon emissions saved were determined. Results showed that treatment S4 had the highest quantity (471 mL/gVS) and quality (63.8% methane) of biogas compared to other ratios after the retention time. A fixed - dome digester of capacity 26 m3, capable of producing 1.3 m3 biogas/day was sized as the appropriate digester for the abattoir. The potential of biogas produced was found to meet 48% and 18% of the current daily electrical, and thermal energy demands at the abattoir respectively. Utilization of biogas at the abattoir was evaluated, and resulted into a saving of 5 tons of wood fuel per year or a saving of 6,500 ton CO2. The investment required for implementing the biogas digester technology was calculated as USD 5,000. The NPV of the biogas digester was found to be USD 39,000 with an IRR of 179% and a B/C of 8.8, hence a worthwhile investment by the abattoir management. The capital recovery period for the digester at an interest rate of 20% was found to be 8 months. In general, it was found technically and economically viable to convert waste to energy at piggery abattoirs in Uganda using anaerobic digestion. The waste to energy technology also reduces carbon emissions and treats the waste generated at the abattoir.