What is particulate and colloidal fouling and how can it be measured?
Particulate or colloidal fouling of reverse osmosis (RO) elements can seriously impair performance by lowering productivity and sometimes salt rejection. An early sign of colloidal fouling is often an increased pressure differential across the system. The source of particulate or colloids in reverse osmosis feedwaters is varied and often includes bacteria, clay, colloidal silica, and iron corrosion products. Pretreatment chemicals used in clarification such as alum, ferric chloride, or cationic polyelectrolytes can also cause fouling if not removed in the clarifier or through proper media filtration. In addition, cationic polymers may coprecipitate with negatively charged antiscalants and foul the membrane. The tendency of a water for fouling is measured with the SDI.
