We are continuing our discussion of ozone applications in the treatment of drinking water. One of these applications is the enhancement coagulation and flocculation which often results in improved filtration and improved turbidity. Rakness has surveyed water treatment plants that use ozone and has found that many of them have observed an improvement in coagulation and filtration. This has been observed as a reduction in chemical use in the coagulation flocculation process. Data from water treatment plants show that pre-ozonation (ozonation of the raw water) was more effective than pre-chlorination to reduce filter effluent turbidities. Besides drinking water plants, operators of aquariums have also observed enhanced filtration with the use of ozone.
Several suggestions have been proposed for the cause of the improved coagulation, but no definitive answer has been accepted. Ozone forms organic compounds with functional groups such as carboxylic acid. These compounds may form complexes with aluminum oxide. Carboxylic functional groups can also complex calcium which may improve adsorption of organics to the metal oxide surfaces. Ozonation of organic compounds may create organic polymers that may enhance coagulation. Ozone can breakdown Fe and Mn which are complexed with organic compounds. The release of the oxidized metals may create a source of natural coagulant.
For a large number of WTP improved particulate removal for filtration has been observed after the installation of ozone generators in terms of lower turbidity, lower particle counts in the filtered water and increased filter runs. In pre-ozonation applications, lower dosages of coagulant have also been observed. This reduction in chemical use can be in the range of 20 to 50%.
Enhanced filtration can be an important economic and performance benefit observed with the use of ozone generators in the treatment of drinking water and other water treatment applications.
Kerwin L. Rakness, “Ozone in Drinking Water Treatment: Process Design, Operation and Optimization”. AWWA 2005
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