Decentralized Vermi-Biofiltration System for Urban Wastewater Valorization: A Techno-Ecological Approach to Household Sewage Management

Urban sanitation in developing economies faces the dual pressures of water scarcity and inadequate sewage infrastructure. This study introduces a decentralized vermi-biofiltration system that integrates anaerobic digestion, vermicomposting (Eisenia fetida), and multi-stage sand/gravel filtration to treat household blackwater and greywater for safe agricultural reuse. The system achieved a 92.3% reduction in chemical oxygen demand (COD) and a 1.4-log removal of Escherichia coli, producing effluent compliant with  World Health Organization irrigation standards (≤1,000 CFU/100 mL). Nutrient recovery analysis revealed concentrations of 4.2 mg/L phosphate (PO43−), 7.8 mg/L ammonium nitrogen (NH4+-N), and 50.5 mg/L potassium (K+), sufficient to offset approximately 35% of synthetic fertilizer demand in urban gardening applications. A techno- economic assessment demonstrated 90% water recovery—equivalent to 12,000 liters per month— with a projected payback period of 2.3 years at scale. System reproducibility was confirmed through modular design (2.5 m3 biodigester volume, 0.15–0.25 mm sand grain size) and adaptive flow regulation via open-source control algorithms. These findings advance the case for low-cost, closed-loop sanitation systems aligned with Sustainable Development Goal 6 and circular economy principles. The results support broader adoption of biodigester toilet technologies in urban and peri-urban communities, offering a safe, scalable, and resource-efficient solution to wastewater management.