Lixin Xie

Dual-stage nanofiltration seawater desalination: water quality, scaling and energy consumption

AbstractA dual-stage nanofiltration (NF) seawater desalination process was investigated as a novel seawater desalination technology, focusing not only on the permeate water quality, but also on the scaling possibility and energy consumption. Dow FilmtecTM NF90 was used in the experiment for its high rejection of total dissolved solids (TDS). The results show that the permeate TDS from the second stage could be as low as 200 mg/L under an optimized condition. The operating pressures were only 3.5 MPa in the first stage and 2.0 MPa in the second stage. Operation pressure had the most significant effects on water permeate flux and TDS. Several indices were calculated to investigate scaling probability. The results indicate that scaling could occur in the first stage. Thus, a prevention method would be needed. The effects of the operating parameters on the energy consumption were also examined. The results indicate that dual-stage NF seawater desalination is a feasible technology in the view of water quality ...

Complexation-Enhanced Boron Removal in a Dual-Stage Nanofiltration Seawater Desalination Process

A complexation-enhanced boron removal method in a dual-stage nanofiltration (NF) seawater desalination process was investigated. A comparative experiment of five different polyols was carried out. Sorbitol was chosen as the complexation additive because of its higher equilibrium constant. The reaction between boron and sorbitol was rapid and only slightly affected by the other ions. Due to the complexation reaction, boron rejection of dual-stage NF seawater desalination process was increased from 35% to 62% in the first stage and from 42% to 55% in the second stage. Boron concentration reached 0.1 mg/L by adjusting the complexation and pH value. Molecular structures were simulated using the molecular simulation technology. The results indicated that molecular structure and molecular size played significant roles in enhancing boron removal. Meanwhile, NaOH and sorbitol had no evident effect on the chemical structure of the membrane surface. The results indicated that complexation is an effective method to reduce boron concentration in a dual-stage NF seawater desalination process.