Pilot-scale study on direct ultrafiltration of raw water for drinking water production and its operating parameter optimization

This study， conducted at the Haikou Jiangdong Water Plant， applied a direct ultrafiltration process to treat the Nandu River water for potable use. Pilot-scale experiments were performed to optimize key operational parameters， including filtration cycle， backwash regime， and chemical-enhanced backwash （CEB） dosing and frequency. Under the optimized condition， the study comprehensively evaluated treatment performance， membrane-fouling characteristics， and techno-economic outcomes. The results showed that with a filtration cycle of 90 min and a high-intensity， short-duration backwash regime （170 L/（m2·h） flux， 150 s air scouring， 10 s combined air-water top backwash， 10 s combined air-water bottom backwash）， together with CEB using 500 mg/L sodium hypochlorite at a frequency of 7 days， the system exhibited robust adaptability and stable performance across varying raw-water qualities. The system maintained regulatory-compliant effluent even when raw-water CODMn reached 7.01 mg/L during high-turbidity periods （≥50 NTU）. However， when raw-water CODMn approached 3.6 mg/L during low-turbidity periods （Mn exceeding the applicable drinking-water standard. Over 42 days of operation， the transmembrane pressure increased by a cumulative 8.48 kPa but stabilized following a short-term high-turbidity perturbation. Membrane-fouling analyses confirmed that the optimized operating conditions effectively limited fouling and identified siliceous-aluminous inorganic residues as the primary irreversible foulant fraction. A techno-economic assessment indicated water production costs of RMB 0.226/m³ （low-turbidity） and RMB 0.243/m³ （high-turbidity）， both lower than the RMB 0.261/m³ estimated for a conventional coagulation-sedimentation-filtration-disinfection process. The operational-parameter framework established in this study provides experimental evidence and technical support for applying direct ultrafiltration as a primary pretreatment unit in engineering practice.