In many process and wastewater applications, reduction of dissolved ions is not required but efficient reduction of colloidal inorganic or organic molecules is.

Ultrafiltration (UF) membrane configurations and system designs are similar to those used in the single-stage RO process. Because the large molecules removed by UF exhibit negligible osmotic pressure, operating pressures are usually much lower than in RO systems. Typical applications include reduction of oil and grease and recovery of valuable contaminants in process waste streams.