Surface water reverse osmosis permeate remineralization via minerals recovery from brines: Insights from a long-term industrial pilot study

Abstract

Application of Assisted-Reverse Electrodialysis (A-RED) technology following low-pressure Reverse Osmosis (LPRO) for permeate remineralization from minerals recovered from the brine was evaluated at the pilot scale. A 3.6 m³/h pilot was tested using brine and permeate streams produced from a three-stage LPRO unit applied to treated water from a surface water drinking water treatment plant. The process presented viable results with permeate mineral content increasing from 6 mg/L CaCO₃ up to values of 1060 mg/L CaCO₃ and from 26 μS/cm up to 1906 μS/cm for hardness and conductivity respectively, allowing for a small footprint industrial system applied to a fraction of the permeate flow to reach the final treated water target hardness value of 90 mg/L CaCO₃. Microcontaminant breakthrough tests of 32 compounds highlighted low levels of micropollutant passage with an overall retention of 92 % while dissolved organic matter (DOM) breakthrough ranged from 12 % to 25 % with a limited impact on bacterial regrowth as measured by Assimilable Organic Carbon (AOC). Scaling up to full-scale plant highlighted a water remineralization cost of 1.56 c€/m³ and a favorable carbon footprint compared to lime and calcite units. Process performance was maintained stable despite changes in influent water quality and temperature over 2000 h of runtime.