Optimization of the startup phase of semi-continuous biogas reactors through co-digestion of Organic Solid Waste (OSW)

This study evaluates biogas production from co-digested organic waste in a bench-scale semi-continuous Continuous Stirred Tank Reactor (CSTR). The use of organic waste in anaerobic digestion (AD) enables sustainable practices that help diversify the energy portfolio and reach decarbonization goals. However, the challenges associated with the operation of anaerobic reactor require studies and guidelines aimed at strategies for establishing biogas plants. This study assesses the production potential at the start of the operation of a Continuous Stirred Tank Reactor (CSTR), using a mixture of organic solid waste (OSW) that includes food waste, olive oil and pasta, selected for their high organic load and lipid-rich composition-was used to assess biogas production potential at startup. Essays were performed to determine biogas production and Biochemical Methane Potential (BMP) for progressive Organic Loading Rates (OLR) added to the semi-continuous reactor. The maximum biogas yield, based on the value obtained in the BMP assay occurred at an OLR of 4.49 gVS/L, while higher rates led to system instability and a significant drop in performance to 22% Volatile Solids (VS) removal remained above 70% and the methane content achieved excellent levels throughout the operation. This study shows the feasibility of using co-digestion of organic waste to produce biogas with excellent methane and highlights the innovative application of progressive OLR ramping as a start-up strategy that stabilizes anaerobic reactor performance, addressing common challenges in biogas plant implementation. Additionally, the results underscore the contribution of biogas to achieving energy sustainability goals and reducing greenhouse gas emissions.