Pilot testing of outside-in UF pretreatment prior to RO for high turbidity seawater desalination

Seawater desalination has become an important way to solve the crisis of fresh water resource. Due to the new developments in membrane technology, reverse osmosis (RO) has gained momentum over the last decade for the desalination of seawater. Proper pretreatment is the most critical factor for successful long-term performance of seawater reverse osmosis plants. The purpose of this pilot testing was to assess the potential of ultrafiltration (UF) prior to RO for high turbidity seawater desalination. The UF systems were set up at the seaside in Yuhuan, Zhejiang province, in China. The Omexell™-SFP was the one of the membranes used. Pilot testing results were obtained on Yuhuan seawater using the outside-in hollow-fiber Omexell™-SFP UF module in dead-end mode. The testing was fed directly by high turbidity seawater for about 50 days, and then turned to use coagulation seawater. The study showed that the UF system provided the permeate water with high and constant quality no matter regardless of feed water; the SDI15 was maintained below 3, meeting the demand for intake water quality of RO. The suitable NaClO concentration dose was beneficial to a filtrate SDI decrease. Other parameters such as total Fe, COD, colloidal Si and total bacterial count were also measured. The pilot rig was operated at different fluxes ranging from 50–100 L/m2.h with and without coagulant addition. Coagulation of raw seawater could help to increase the flux of the UF membrane and provide filtered seawater in a steady-state condition.