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.