Operating parameters optimization of combined UF/NF dual-membrane process for brackish water treatment and its application performance in municipal drinking water treatment plant

As an important water resource, brackish water has been extensively utilized in the industry. However, there are few cases of municipal potable water treatment plants that use low chloride content brackish water as the source. In this paper, the brackish water treatment efficiency of ultrafiltration (UF)/nanofiltration (NF) dual-membrane process was evaluated in a municipal potable water treatment plant, combining with a pilot optimization experiment. Results showed that UF guaranteed the inlet water quality of NF and NF could efficiently reject organics and salts, with a chloride removal over 95 %. Pilot experiment showed that the UF membrane flux decreased only 12 % after continuously 30-days operation under the optimized UF operation conditions, effectively extending the chemical cleaning interval. Response surface method was adopted in the NF removal efficiency and energy consumption optimization. With the increase of feed water conductivity, the influences of pressure and recovery on the removal efficiency were strengthened, and the removal efficiency could be regulated over a wider range. When the conductivity was less than 3500 μS/cm, NF could perform high treatment efficiency under the operation pressure of 0.65−0.85 MPa and recovery of 55–70 % . Besides, as feed conductivity increased, it was necessary to increase the pressure and reduce the recovery within this range to maintain efficient operation. This paper will provide a guidance for the UF/NF dual-membrane process design and operational optimization.