The use of ozone prior to bio filtration as the primary disinfectant leads to a more complete disinfection and a lower disinfectant concentration.
Ozone is an extremely strong oxidizing agent and acts much quicker than chlorine and any other chemical agent in eliminating inorganic matter. Both surface water and ground water tend to contain micro-pollutants like pesticides that ozone effectively eliminates by oxidation.
Ozone is however less potent in mineralization of natural organic matter (NOM) which is normally present in all water sources. Yet natural organic matter must be removed first in water treatment particularly to produce pure drinking water. Natural organic matter is what creates direct problems like odor and taste in water, plus indirect problems such as bacterial regrowth in water distribution systems and formation of organic disinfection byproducts.
Ozonation however, partly oxidizes organic matter making it more easily biodegradable. This way, ozone improves the process of removing natural organic matter when it is used as a pre-oxidant. Bio filtration may then follow ozonation to achieve complete removal of inorganic matter since oxidation forms insoluble compounds that need to be eliminated during subsequent steps in the water purification process.
Water treatment with a chemical disinfectant initiates a reaction between organic material and the disinfectant thus creating disinfection byproducts (DBP) in the process. Using chorine as the disinfectant leads to the formation of chlorinated organic DBPs such as trihalomethanes (THM). Using ozone on the other hand leads to organic DBPs like ketones and aldehydes which are easily degraded (up to 100 percent) in a biofilter. This way, the use of ozone as the disinfectant creates safer disinfection byproducts that do not present any risk of noncompliance to drinking water standards.
Where chlorine is used as the disinfectant, prior ozonation is recommended for pre-oxidation to reduce the amount of disinfection byproducts in the conventional disinfection system.
Inorganic compounds such as iron and manganese; and natural organic matter, can form compounds that create odor and taste in water.
Most of these odor and taste forming compounds tend to be very resistant, making their elimination to be a very intensive process. While several processes such as oxidation, granular active carbon (GAC) filtration, aeration or sand filtration can be individually appropriate for the elimination of taste and odor, a combination of these techniques normally provide the best results.
Like in the case of disinfection (above), pre-oxidation using ozone; followed by activated carbon (GAC) filtration, improves the purity and overall quality of the filtered water.