From waste to resource: A system-dynamics analysis of biogas and water reuse synergies in coconut-processing wastewater treatment

Industrial expansion and increasing water scarcity in Southeast Asia are pushing agro-industrial facilities to adopt wastewater solutions that recover both energy and water at a reasonable cost. Unlike prior theoretical or static techno-economic studies, this study develops a system-dynamics economic model calibrated with five years of operational data from three full-scale coconut-processing membrane bioreactor (MBR) plants. The model explicitly couples influent variability, aeration demand, and load-dependent capital and operating expenditure to monthly cost and revenue flows. Four operational configurations were evaluated: baseline treatment, biogas-to-electricity recovery, treated-water reuse, and a combined pathway, together with stress tests that doubled hydraulic and organic loads. The central contribution is the introduction of deterministic economic threshold maps, which identify the exact load conditions at which decentralized wastewater systems transition from stable operation to financial stress. Across all plants, the combined recovery configuration delivered the strongest performance, reducing net treatment cost by up to 70% while maintaining stability under fluctuating loads and utility tariffs. By integrating long-term industrial data with dynamic simulation and threshold mapping, this work provides a validated, decision-oriented framework for designing decentralized wastewater systems as resilient, resource-positive infrastructure rather than cost centres.