What are the possible consequences of operating an RO system at a recovery rate that is too high?

Operating an RO system at a recovery rate that is too high can lead to several negative consequences, primarily related to increased fouling and scaling potential. The recovery rate is the percentage of feed water that is recovered as permeate (product water). A higher recovery rate means that less water is discharged as brine (concentrate). When the recovery rate is too high, the concentration of dissolved salts and other impurities in the remaining brine stream increases significantly. This leads to a higher risk of scaling, as the concentration of scale-forming ions, such as calcium, magnesium, and silica, exceeds their solubility limits. The increased concentration of impurities also increases the potential for fouling, as suspended solids, colloids, and organic matter accumulate on the membrane surface. Both scaling and fouling reduce permeate flux, increase pressure drop across the membranes, and shorten membrane life. High recovery rates can also lead to increased concentration polarization at the membrane surface, which is the accumulation of salts near the membrane, further exacerbating scaling and fouling. In severe cases, operating at an excessively high recovery rate can cause irreversible membrane damage, requiring premature membrane replacement. Therefore, it is important to operate the RO system within its design recovery rate and to carefully monitor water chemistry and membrane performance to prevent scaling and fouling.