About ultrafiltration: introduction

Combine with microfiltration, ultrafiltration (UF) is a low pressure membrane. UF is usually used for potable water treatment, biological wastewater treatment and also for ultrapure water production. The latter is common method for metal or electronic industries. UF typically operates within 40-1000 kPa (5.8-145 psi) (0.4-10 bar) having molecular weight cut off (MWCO) ranging from 1 kDa to 100 kDa (kilo Dalton).

MWCO is a term used to define 90% of molecular weight of a compound can be retained by the UF. Since UF have higher pore size or MWCO than reverse osmosis (RO), it usually produce higher flux. However, since RO has denser pore size, thus the rejection is become more excellent, even a virus may be filtered out to result a high ultrapure water.

Although in some countries the application of UF has become a priority, still in most countries, UF is considered to be an alternative treatment replacing conventional treatment such as conventional filtration, coagulation-flocculation. When UF takes charge, it is used to remove coarse particles, debris causing turbidity, microorganisms and mainly natural organic matter (NOM). Natural organic matter is usually a main subject when it talks UF research, including my research.

Some people, experts, industry practitioners like UF because of its simplicity in operation, and the opportunity for development and increasing flux and the removal of unwanted pollutants. Weimin Xi (2001) adds that MF as well as UF are simple to do since they do not involve a phase change or interphase mass transfer and may be the process that can be used for complete recovery of TiO₂ from water.

Of course one of the main drawbacks of UF which is fouling will also have to be covered in how mitigating as optimum as possible the fouling. Although several authors stated that membrane operation cost lower than conventional treatment, I am still not able to prove that in my own country.

One of the priority problem related to UF is fouling due to NOM. Thus it affects the flux. Generally, the ability of UF to remove NOM depends on several factors, MWCO of the membrane, physical and chemical properties of NOM, interaction between NOM and membrane surface.