LAUSR

Abstract This study evaluated ‘high-pH precipitation treatment’ of a reverse osmosis (RO) concentrate followed by secondary RO treatment to increase overall water recovery in an existing inland desalination system. In contrast with previous studies that used calcium dominated surface waters, this study dealt with magnesium dominated groundwater. The high-pH process removed scale-forming precursors including magnesium, calcium, strontium, barium and SiO2 from primary RO concentrate by precipitation and adsorption/enmeshment. Lime and soda ash were determined to be the superior caustic agents when compared to sodium hydroxide for the high pH demineralization process. Following ‘high-pH precipitation treatment’, pH readjustment and antiscalant addition, the use of secondary RO enabled the overall water recovery to be increased from 80 to 97%. In addition, this study evaluated CaCO3 and CaO recovery from the precipitated sludge through CO2 gas injection to selectively dissolve magnesium.