The Physio-chemical methods used for treating Industrial waste water are:

1. Reverse Osmosis.
2. Electrodialysis.
3. Chemical oxidation.
4. Ion exchange.
5. Thermal reduction.
6. Air stripping.

When a permeable membrane separates a dilute and a concentrated solution, the osmotic pressure drives the water molecules from the dilute solution, through the membrane to establish an equilibrium. This natural response is reversed in reverse osmosis process, where the waste water containing dissolved salts as filtered through a semipermeable membrane such as cellulose acetate at a pressure higher than the osmotic pressure.

In electrodialysis, the flow of iconic substances is initiated by providing an electrical potential between two electrodes and the substances are filtered by using an ion-selective membrane ahead of the electrodes. The separation of substances in this process requires sets of alternate cation and anion permeable membranes in between the electrodes. Electrodialysis also requires some pre-treatment as in Reverse osmosis.

The chemical oxidation consists of addition of chemicals like chlorine and ozone to reduce the BOD loading on the subsequent biological process or to reduce substances like ammonia, cyanide etc.

Ion exchange involves similar passage of waste water through a fixed synthetic ion exchange resin bed, where some of the undesirable cations or anions of the waste are exchanged for Sodium or Hydrogen ions of the resin. Ion exchange bed requires regeneration and special care should be taken for the treatment of waste produced due to regeneration.

Thermal reduction involves the burning and thereby oxidation of some refractory and toxic substances(like organic cyanide).

Air stripping involves the passage of a liquid waste through a packed tower, which is equipped with an air blower at the bottom. This process is a modification of aeration process used for the removal of gases from the waste water.