*3.1.1.2 Ultrafiltration*

The performance of ultrafiltration (UF) processes are currently receiving increasing recognition as a pretreatment for desalination and membrane bioreactor applications. UF like MF uses physical sieving as a separation mechanism. The pore size, molecular weight cut-off (MWCO) and pressure for a UF membrane filtration ranges from 0.05 μm to 1 nm, 1–500 kDa and an operating pressure of 1–7 bar [47]. In effect, UF with a definite MWCO are impermeable to compounds with molecular weights exceeding the MWCO and have demonstrated a 3–6 log removal of chlorine resistant protozoan cysts, colloids, viruses, and coliform bacteria. The use of MF and UF as pretreatment to reverse osmosis (RO) has progressively arose at an industrial scale. Both could serve as pretreatment strategies for NF and RO processes for the reduction of membrane fouling, which is applied as a post treatment to chemical precipitation of organic chemical removal, pH adjustment, and phosphorus, hardness, and metal removal. Fouling is extremely distinguished in UF applications, due to the high molecular weight of fractions retained in relation with the small osmotic pressure differentials, and liquid phase diffusivity. However, this does not negatively influence the demand for UF's, as any design, configuration and application will be fouled [49, 50]. The configuration for application could be influenced by the mechanical stability, hydrodynamic requirement, and cost implications.
