A field study of desalination of high-salinity surface brackish water via an RO-NF hybrid system

Abstract

In this work, a pilot-scale membrane desalination demonstration system for producing drinking water from surface brackish water with a total dissolved solids (TDS) of ≤ 10 g/L was designed and constructed. The production capacity and water recovery were at least 1 m3/h and 50%, respectively. Brackish water was pretreated with microflocculation – precision filtration – ultrafiltration, and the quality of the produced water met the feed water requirements of nanofiltration (NF)/reverse osmosis (RO). The performances of various design configurations, including single NF, single RO, and NF-RO hybrid systems, were evaluated and compared in terms of water recovery and product water TDS. The hybrid RO-NF systems were found to be more effective than either NF or RO alone, and the 4RO-4NF design configuration was most favorable. At a TDS of 10 g/L in the feed, the processing capacity and product water TDS of the 4RO-4NF hybrid system was able to meet the design specs at a feed flow rate of 2 m3/h and an operating pressure of 1.5 MPa. Its long-term stability was examined as well, and it was demonstrated that the desalination performance of the system was mainly affected by seasonal temperature changes and rainfall. The total process cost was estimated to be $1.56/m3, which is considered economically suitable for remote areas where safe drinking water cannot be provided centrally.