Colored water is typically caused by a combination of dissolved organic matter, which absorbs visible light, and suspended colloidal and particulate matter, which scatters light. Apparent color is due to both light absorption and light scattering. True color is exclusively caused by dissolved matter. Typically these materials are organic in nature and contain aromatic rings. Typical organics falling into this classification include humic and fulvic acid.
Ozone effectively reduces true color.
By reacting the unsaturated groups and cleaving the carbon-carbon double bonds within organic compounds, ozone produces aldehydes, ketones and acids, depending on the groups affected, the ozone dosage and contact conditions. When oxidized, the resulting organics absorb light differently from the original material, resulting in a reduction of true color. Colloidal and particulate organic matter can be reduced by filtration to minimize light scattering. Ozone's microflocculation effect can aid in the coagulation of organic colloidal and particulate matter which, in turn, increases filtration efficiency. If the BDOC is not removed or the effluent sufficiently chlorinated to meet organic demand, biological regrowth can occur in the distribution system.