purpose of oxidation-reduction treatments

Physical-chemical oxidation is used in the treatment of all types of water for a range of purposes:

• for disinfection before household or industrial using in order to avoid any danger of bacterial contamination;
• for precipitating dissolved compounds (iron, manganese, sulphides);
• for breaking down organic compounds and especially those responsible for colour, odour and taste in water, those that are toxic and, more generally, those that contribute to the water’s chemical oxygen demand;
• to eliminate ammonia nitrogen;
• to convert non-biodegradable pollution into substances that can be assimilated by bacteria in a subsequent biological treatment.

The choice of oxidant to be used for the different cases considered will be dictated by:

• the highest possible oxidising capacity;
• ability to select the targeted pollution;
• control over side-effects in terms of induced toxicity;
• cost of associated treatment must not be prohibitive.

Physical-chemical reduction is rarely used. It has very specific applications and, mainly:

• the removal of dissolved oxygen in order to limit the risk of corrosion in industrial water systems;
• converting hexavalent chromium into trivalent chromium;
• destruction residual oxidants.