Sustainable Wastewater Treatment Through Anaerobic Digestion in the Instant Coffee Industry: A Techno-Economic and Environmental Assessment

The coffee industry generates wastewater with high organic loads, which represents both an environmental challenge and a potential resource. This study proposes a novel, integrated solution for an instant coffee plant in Ecuador by incorporating anaerobic digestion into the treatment train. The approach uniquely combines rigorous kinetic analysis with a comprehensive techno-economic and sustainability assessment. Long-term operation of upflow anaerobic filters confirmed the superior stability and performance of the mesophilic regime. Under these conditions, the process achieved a methane yield of 200.5 mLCH4 g−1COD and a chemical oxygen demand (COD) removal efficiency of 64.1%. The experimental data fitted to the modified Stover–Kincannon and Grau second-order kinetic models (R2 > 0.95) validating the robustness of the mesophilic operation. For the technological proposal, a hydraulic retention time of 7.3 days and an organic loading rate of 1.03 kgCOD m−3 d−1 were established. The economic evaluation confirms that a minimum price of USD 171 per 60 kgbag is required to achieve a positive net present value with a payback period of 5.47 years. Furthermore, the system transitions the facility’s energy profile to net-positive status, with an energy recovery ratio of 1.67, and strengthens the environmental sustainability of the proposal. It is concluded that anaerobic digestion is a viable technology from technical, economic, and environmental perspectives, enhancing the performance of the instant coffee industry and generating added value from highly polluting waste.