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.

► The paper describes an improved high water recovery RO process. ► Scaling species are removed from the RO concentrate by a fluidized bed (FBR) air stripping system. ► Very high precipitation conversion of CaCO3 is achieved. ► Desalination of the scale-free concentrate enables an overall water recovery exceeding 95%.