High Total Dissolved Solids Water Treatment by Charged Nanofiltration Membranes Relating to Power Plant Applications.

Selective desalination through nanofiltration (NF) is of great interest for many industrial applications including reuse of power plant scrubber wastewater and treatment of water containing high concentrations of TDS (total dissolved solids). This work seeks to understand the effect ion interactions at the membrane interface have on rejection and flux performance of charged NF membranes. NF membranes were also effective for low energy desalination of scrubber wastewater from Georgia Power Plant Bowen, composed primarily of Ca2+, Mg2+, Cl-, and SO4 2-. As NF membranes have the capability for selective separations, 80% water recovery was achieved experimentally while maintaining an overall rejection of over 60% for Ca2+ and Cl-. The occurrence of CaSO4 precipitation at high water recovery was observed. The effect of precipitation on osmotic pressure and the effect of Cl- counterions on increasing gypsum solubility were explored for water recovery operation. This work expands on a previous work on the topics of desalination of multi-ionic solutions by incorporating the use of large scale membrane modules (0.59 m2) with several synthetic solutions as well as actual scrubber water containing precipitating elements, Ca2+ and SO4 2-. It was observed that the spiral wound membrane modules maintained a stable water permeability over the 144 day course of tests.