High recovery brackish water desalination process devoid of precipitation chemicals

The present paper describes pilot plant development of a novel process enabling increase of water recovery in brackish water desalination without using any chemicals. This is achieved by precipitating the scaling salts of a carbonate-rich concentrate by increasing the pH through air stripping of CO₂ from the solution. Additional permeate is extracted from the treated concentrate by a secondary RO unit. The pilot plant data confirmed that a precipitation conversion of CaCO₃ of at least 70% can be achieved by the aeration process at a retention time of about 2 h in the precipitation vessel. Integration of the concentrate treatment with the primary desalination process enabled increase of the overall water recovery from 78% to 90%. Higher recoveries exceeding 95% can be anticipated in processing concentrate solutions of sufficiently high carbonate content.