COLOR IN WATER
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. Dissolved matter exclusively causes true color. Organic matter, which absorbs light within the 300 to 400 nm wavelengths, and fluoresces in the range of 200 to 400 nm, creates the appearance of color in water. Typically, these materials are organic in nature and contain aromatic rings. Typical organics falling into this classification include humic and fulvic acid.
Ozone is most effective at reducing 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 than the original material, resulting in a reduction of true color.
Colloidal and particulate organic matter can bc 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.
Oxidation of organics can result in increased biodegradable organic carbon (BDOC) which is measured as assimilable organic carbon (AOC). If the BDOC is not removed or the effluent sufficiently chlorinated to meet organic demand, biological regrowth can occur in the distribution system.
In addition to oxidation, other technologies can be used to remove organic-related color from water supplies. These methods include coagulation (using hydrolyzing metals such as alum and metal salts, followed by flocculation and filtration), activated carbon adsorption, and membrane filtration technologies (including ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO)).