Improved high recovery brackish water desalination process based on fluidized bed air stripping

Very high water recoveries can be achieved in brackish water RO desalination by air stripping of a carbonate-rich concentrate which provides high pH conditions for precipitating calcium hardness without necessitating the use of chemicals. The scale-free concentrate solution can be then processed with a secondary RO unit to recover additional product. Simple precipitation in an MSMPR crystallizer requires relatively high retention times of the order of 2. h. The present paper describes an improved high recovery process in which precipitation is carried out in a fluidized bed (FBR) air stripping system. Experimental results are presented, showing that FBR crystallization enables very high precipitation conversion of calcium carbonate reaching 90% at considerably reduced retention times of the order of 15. min.