Greywater filtration using water treatment sludge: optimization of operating parameters

The growing demand for water, driven by rapid urbanization and industrialization, necessitates sustainable wastewater management solutions. Greywater, comprising 50–80% of domestic wastewater, presents a valuable opportunity for reuse due to its relatively low pollutant load. This study evaluates the operational performance and applicability of a greywater filtration system employing water treatment sludge (WTS) as a filter medium. The effects of three parameters, namely hydraulic loading rate (HLR), WTS media depth, and WTS particle size were evaluated through long-term column experiments treating real settled greywater. Response Surface Methodology (RSM) based on the Box–Behnken Design was employed to analyse and optimize the system performance. The filters achieved significant pollutant removal, with effluent turbidity, COD, BOD, NH₄⁺-N, and PO₄³−-P reduced to 2.2 NTU, 74, 56, 3.88, and 0.08 mg/L, respectively, and a cumulative filtered volume of 460 L under optimum conditions – HLR 6 m³/m²/day, WTS depth 18 cm, and WTS size 0.98 mm. Better performance was observed at lower HLRs, finer media sizes, and moderate to greater media depths. This study demonstrates that WTS-based filters offer a cost-effective, resource-efficient, and sustainable solution for decentralized greywater treatment, supporting circular economy principles and improving access to water reuse technologies in resource-limited settings.