SCALE FORMATION PROGNOSIS AND CLEANING PROCEDURE SCHEDULES IN REVERSE-OSMOSIS SYSTEMS OPERATION

Sparingly soluble salts scale control remains to be an important problem in many cases of RO brackish water desalination, influencing the feedwater pretreatment scheme selection. The conditions of crystal nucleation and scale formation in industrial modules are still unknown. The author's new conception of scaling mechanism in spiral wound modules has been presented. The driving force for crystal formation is considered to be a high supersaturation degree reached through concentration of bulk solution in the deadlocks i.e. the spots where the spacer contacts the membrane surface. The experimental results enable us to calculate CaSO4 and CaCO3 scale growth rates and estimate the inhibitors' effectiveness quantitatively for various brine compositions. The experimental relationships obtained can predict CaSO4 scale and membrane parameters decrease through scaling. The volume of cleaning solution needed for washing procedure can be also calculated. The experimental study conducted used spiral wound modules with cellulose acetate and composite membranes manufactured in the USSR. In order to achieve safe operational performance and economical membrane life the feedwater pretreatment (inhibitor dosage) should be combined with timely washing procedures.