A bench-scale assessment of enhanced coagulation-filtration for greywater in decentralized system

• Synthetic greywater served as a model for greywater reuse research. • Enhanced coagulation outperforms simple process, verified by statistical analysis. • Optimized coagulation with filtration meets regulatory requirements for water reuse. • Accurate analysis of greywater samples and legal reuse framework is presented. • Greywater reuse improves urban water system adaptability and resilience. This study evaluates the effectiveness of an enhanced coagulation-filtration (CF) process with post-filtration for treating bathroom greywater (BGW) for non-potable reuse applications. A bench-scale experiment assessed two cost-effective inorganic coagulants, ferric chloride (FeCl₃) and hydrated lime (Ca(OH)₂), as well as their combination, using synthetic bathroom greywater (SBGW) to determine optimal treatment conditions. The CF process, with an optimal combined concentration of FeCl₃ at 250 mgL -1 and Ca(OH)₂ at 148 mgL -1 achieved an ideal zeta potential range of -5 mV to 5 mV for SBGW, resulting in superior impurities removal. Jar tests under varying conditions (mixing speed, contact time, and sedimentation) confirmed these findings, and optimized conditions were validated with real bathroom greywater (RBGW) samples, exhibiting slight variations due to BGW quality differences. The FeCl₃ dosage was adjusted (220-250 mgL -1 ), while the Ca(OH) 2 dose was kept constant (148 mgL -1 ) for all RBGWs. The tested enhanced CF process demonstrated high removal efficiencies for turbidity (99±0.5%), chemical oxygen demand (COD) (96±3.4%), biochemical oxygen demand (BOD 5 ) (98±1.3%), and anionic detergents (99±0.5%) values of BGW samples, as well as reducing the number of colonies for Escherichia coli (99%), and Coliforms/Total Count TTC (99%), meeting EU Regulation 2020/741 requirements for water reuse in irrigation. Statistical analysis supports the novelty of enhanced CF, proving its superior effectiveness compared to single ferric chloride coagulation method, making it a promising decentralized greywater treatment solution for European countries.