Membrane Processes Classification
- 1. Micro-Filtration (MF)
-
Microfiltration removes particles higher than 0,08-2 ?m and operates within a range of 7-100 kPa.
Microfiltration is used to remove residual suspended solids (SS), to remove bacteria
in order to condition the water for effective disinfection and as a pre-treatment step for reverse osmosis.
Relatively recent developments are membrane bioreactors (MBR) which combine microfiltration and a bioreactor for biological treatment.
- 2. Ultra-Filtration (UF)
-
Ultrafiltration removes particles higher than 0,005-2 ?m and operates within a range of 70-700kPa.
Ultrafiltration is used for many of the same applications as microfiltration.
Some ultrafiltration membranes have also been used to remove dissolved compounds with high molecular weight,
such as proteins and carbohydrates. In addition, they are able to remove viruses and some endotoxins.
- 3. Nano-Filtration (NF)
-
Nano-filtration is also known as ˇ°looseˇ± RO and can reject particles smaller than 0,001 ?m.
Nano-filtration is used for the removal of selected dissolved constituents from wastewater.
NF is primarily developed as a membrane softening process which offers an alternative to chemical softening.
Likewise, nano-filtration can be used as a pre-treatment before directed reverse osmosis.
The main objectives of NF pre-treatment are: (1) minimize particulate and microbial fouling of the RO membranes by removal
of turbidity and bacteria, (2) prevent scaling by removal of the hardness ions,
(3) lower the operating pressure of the RO process by reducing the feed-water total dissolved solids (TDS) concentration.
- 4. Reverse Osmosis (RO)
-
Reverse osmosis is commonly used for desalination. As well, RO is commonly used for the removal
of dissolved constituents from wastewater remaining after advanced treatment with microfiltration.
RO excludes ions but requires high pressures to produce deionized water (850-7000 kPa).
