Unlike reverse osmosis and nanofiltration, the recovery of the microfiltration process is not limited by the formation of _____ or the precipitation of _____.

• A. scale, salts
• B. iron fouling, calcium carbonate
• C. silica fouling, carbonates
• D. organic fouling, salts

Answer: (A)

The question is about what limits recovery in different membrane processes. In desalination-type membranes like reverse osmosis and nanofiltration, high pressure drives water through the membrane while salts are mostly rejected. The feed water near the membrane becomes highly concentrated, so sparingly soluble salts can reach their solubility limit and precipitate as scale on the membrane surface, which blocks pores and reduces flux. That mineral-scale formation and salt precipitation are major factors that cap how much water you can recover.

Microfiltration, on the other hand, uses much larger pores and operates at lower pressures, so it mainly acts as a barrier to suspended solids, bacteria, and some colloids. It doesn’t rely on rejecting dissolved salts, so the feedwater minerals are less likely to precipitate as scale on the membrane. Therefore, the recovery of microfiltration isn’t limited by scale formation or salt precipitation in the same way as RO/NF. The primary fouling risks for MF are organic, biofilm, and particulate fouling, not mineral scaling.