Compact accelerated precipitation softening (CAPS) as a pretreatment for membrane desalination .1. Softening by NaOH

This study examines the application of compact accelerated precipitation softening (CAPS)-a previously developed process-as a pretreatment for membrane desalination. In this CAPS process, rapid precipitation of calcium carbonate is achieved by cake filtration. The importance of this pretreatment step lies in the fact that softening (by NaOH in this case) facilitates an increase of the recovery ratio in membrane desalination by decreasing the potential for scaling. In addition, CAPS serves as an effective filtration step, reducing both turbidity and the silt density index and hence the potential for membrane fouling.