ECONOMICAL AND ENVIRONMENTAL BENEFITS OF POINT-OF-USE NaCl BRINE REUSE BY NEW MEMBRANE TECHNOLOGY

Abstract

Cation exchange water softening is one of the most widely used technologies of water treatment. However, its environmental impact related to discharge of highly concentrated regeneration brine draws more attention as overall quality and availability of water resources decreases. Bearing in mind high levels of reusable NaCl in brine discharge, technology that will reduce the environmental impact and help reuse brine is required. To develop such technology composition of spent brine solution from Na-cation exchanger was investigated and conditioning of such solution with use of nanofiltration membranes of different types under different temperatures, pressures and recovery values was tested. Results show that optimal conditions for NaCl recovery include usage of DuPont (Dow) Filmtec Fortilife XC-N membrane elements at temperature 23-27 °С, pressure of 23-25 bar and recovery of 55-60 %. Under these conditions purity of NaCl in permeate over 90 % and productivity by NaCl of 13.1 kg/h were achieved. Principal technological scheme of the process of membrane conditioning of the spent regeneration solution was proposed that allows achieving reduction of NaCl consumption by 40 % and reduction of NaCl discharge into sewage by 72 % with corresponding economic and environmental benefits.