Updated: July 2002

1. Purpose

Membrane Separation is a unit process to remove or recover dissolved matter or suspended matter in the wastewater by using porous high molecular weight membranes, ceramic membranes, etc. For this purpose, microfiltration (MF), ultrafiltration (UF) and reverse osmosis (RO) have practical application. In the field of industrial wastewater treatment, UF membranes have been often used to remove suspended matter from the wastewater, or separate biologically treated liquid without using a sedimentation tank. Also the RO membrane (loose RO membrane) process is being put into practical use for the purpose of removing COD and calorific components from the wastewater.

2. Types

The membranes used in the field of wastewater treatment are the microfiltration membrane, ultrafiltration membrane and the reverse osmosis membrane (specially the loose RO membrane). These are applied to the following range:

There are modules suitable for each application. For MF and UF, flat modules and tubular modules are used respectively, while, for RO, a tubular type, spiral type and hollow fiber type are put into practice. Materials practically used for membranes are high molecular weight materials such as cellulose, acrylonitrile and polysulfone as well as inorganic materials like ceramic.

3. Example

Refer to the photo given below for an example of the ultrafiltration facilities (4,000 m³/d) to separate and remove COD and calorific components in the waste-water discharged from the pulp and paper plant (pulp bleaching process).