Full-scale polishing systems
Prior to the development of MBR technology, clarification and substantial disinfection of wastewater was achieved by employing microfiltration (MF) or, most often, ultrafiltration (UF) downstream of a classical activated sludge (CAS) process. This ‘non-integrated’ combination of membrane technology with biological treatment is widely used in water reuse applications, and is often preferred over MBR technology since the membrane component can simply be placed downstream of the secondary clarifier with no further modification of the existing infrastructure.
There are three types of water reuse applications, where wastewater is recovered and reused for some purpose:
- Non-potable reuse (NPR), where the recovered water is used for some purpose other than potable supply (e.g. irrigation, industrial process water, etc)
- Indirect potable reuse (IPR), where the recovered water passes through an ‘environmental buffer’ before being used as a supply of potable water, and
- Direct potable reuse (DPR), where the recovered water is used as a potable water supply without passing through an environmental buffer.
IPR and DPR systems employ municipal wastewater as the feed, and are subject to very high treated water quality standards. NPR can either be based on industrial effluents, where the product water is most often reused on site, or municipal wastewater.