What Is Membrane Cleaning? A Wastewater Treatment Glossary

Membrane cleaning is an effective way to prevent membrane fouling and to restore the performance of fouled membranes. Cleaning methods fall into two categories: physical and chemical. Physical cleaning includes forward flushing, in which feed liquid is passed at low pressure and high flow rate during operation to scour contaminants off the membrane surface, and backflushing, in which the feed inlet and the concentrate outlet are reversed so that feed liquid at low pressure and high flow rate dislodges contaminants trapped in dead zones that forward flushing cannot reach. For hollow-fibre ultrafiltration modules, the feed inlet and the permeate outlet are reversed and pure solvent is flushed through at a pressure above the operating pressure. Chemical cleaning uses acids, alkalis, enzymes, complexing agents, surfactants or disinfectants to clean the membrane surface. Physical cleaning must be carried out first; then, once the nature of the foulant has been identified, the optimum cleaning agent, concentration, temperature, contact time and cleaning method that will not damage the membrane are selected. After cleaning, the membrane is rinsed with pure water until no chemical cleaning agent remains before it is put back into service.