Membrane is a thin layer of material that is capable of separating compounds as a function of physical and chemical properties when a driving force is applied across the membrane, which has been widely used in a wide range of applications in water industry . Membrane can be classified by the range of compounds separated and the driving forces employed. For example, microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are four membrane processes that use pressure to transport water across the membrane. MF membranes are capable of removing suspended particles, colloids, and bacteria, while UF and NF membranes can remove macromolecules/natural organic matter and dissociated acids/divalent ions/sugars/pharmaceuticals, respectively. RO membranes retain many solutes as water permeates through the membrane.
Membrane History in Water in the US
- Prior to 1990 mostly RO in industrial applications
- Historically, smaller facilities (< 1 mgd)
- 1st Significant MF/UF System in North America in 1993 (Saratoga, CA – 3.6 mgd)
- Membrane bioreactor emerged in early 1990’s
- In-land brackish desalination in mid 1990’s
- Over 250 membrane WTP now on-line
- Trend is to more, and larger facilities ( Minneapolis – 70 and 95 mgd, Singapore – 72 mgd).