Despite all efforts to protect the RO System from fouling and loss of flux, eventually the membranes will require chemical cleaning. A well-designed RO System will include provisions for a cleaning skid to facilitate the cleaning process. The skid should include a chemical tank, solution heater, recirculating pump, drains, hoses, and all other connection and fittings required accomplishing a complete chemical cleaning of the RO modules.

Various chemical cleaning agents are available for maintaining RO membranes. The type and amount of foulant will dictate the most effective cleaning agent. Acid cleaners’ best remove mineral scale deposits. Hydrogen peroxide is commonly used to clean and sanitize membranes to correct or prevent biofouling problems. In some cases, a mild solvent such as methanol is used. Because of the number of variables involved in the selection and application of these cleaning agents, contact the membrane manufacturer, equipment supplier, or a qualified chemical consultant for specific advice and recommendations on how to accomplish an effective cleaning.

The operation of the RO System should be carefully monitored to predict when the membranes would require cleaning. As a rule of thumb, cleaning is indicated when the normalized flux rate decreases by 10%. Under ideal condition, assuming that the RO pretreatment system is properly designed and operated, the frequency between membrane cleanings should be 3 months or more. Cleaning every 1 to 3 months is considered a fair performance, and suggests that some improvements in the pretreatment system should be considered. Cleaning frequencies every month or more indicate a change in raw water quality, a problem with the pretreatment system, or a problem with the operation of the RO unit.