Scaling Multi Substrate Biogas Systems for National Energy Security and Circular Economy Transition in Sri Lanka: A Case Study

Abstract

: This Case study is structured research of the effectiveness of biogas production and environmental cleanup ability of optimized Slaughterhouse wastes with multi-substrate anaerobic co-digestion systems within a Sri Lankan emerging design of a circular economy model. The five 1L working volume laboratory-scale fixed bed batch reactors were managed to act in the mesophilic environment (35 +/- 2 o C) and with the 21 days of hydraulic retention time. The combinations of substrates that were used involved, poultry manure-fish waste- chicken waste (50:20:30), poultry manure-fish waste (50:50), quaternary mixture (25:25:25:25), beef-centric blend (40:30:30) and plant-animal hybrid (50:50). As a whole, an extensive physicochemical characterization was done using reflux colorimetric closed reflux COD analysis, gas chromatography featuring biogas composition, and volumetric analysis using precision syringe displacement methodology. The combination of 3 substrates (50:20:30) displayed very high methanogenic activity (55 % CH4) that was significantly higher than in binary (52% CH4), quaternary (53 % CH4) and beef-based-predominant (50 % CH4) and lignocellulose-based systems (48% CH4). All the treatment run at 59.94- 60.05 % efficiency rate in the reduction of COD, which was uniformly achieved via mineralization of all organic matter (Initial COD: 4.38-10.98 g/L; Final COD: 1.75-4.39 g/L). The results showed that the biogas was of the correct balance (55:40) of CH4 and CO2 low content of inhibitory complex (H2S: 0.5-2%; NH3: 0.5-1%). Extrapolating to the national level, an estimate of the potential biogas production of 245106 m3 per year that is worth 1348 GWh capacity of renewable power is obtained. This is a great step towards the Sri Lankan government requirement of 70% renewable energy target by 2030. The economic modelling depicts the recapture of the capital in 2-3 years with operating cost of USD 0.702.50 m-3. Significant pollution abatement (10% organic load reduction) and green- house gas mitigation (reduction of GWP or green-house gas emissions most comparable to 25x CO2) is shown to be done by environmental impact assessment on methane capture. An anaerobic co-digestion is technologically feasible and economically sustainable solution to integrated waste-to-energy systems which provides simultaneous environmental cleanup of the contaminated sites and renewable energy production whilst the co-digestion is within the sustainable development goals of Sri Lanka and sustainable transition towards a circular bioeconomy.