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Technical Description Floating solids which surface during the clarification cycle are not lost during normal operation, but are returned to the mixed liquor each sludge-return cycle in the following manner: The supernatant is pumped out of the clarifier except for the top three inches that remain on the surface of the sludge volume. The entire sludge volume, except that which cannot reach the vo- lute of the return pump, is returned to the aeration chamber by the sludge return pump. The re- maining sludge and floatables. now settled on the tank bottom, are weired back to the aeration chamber during the MLT pump overrun on the next batch cycle. After settling has occurred, the microprocessor initiates the supernatant transfer pump (SNT), which transfers the supernatant into the chlorine contact chamber. During the supernatant transit, ozone is injected into a distribution manifold in the bottom of the ozone contact chamber. Ozone injection continues for 40 minutes after the chamber is filled. NOTE. Following are the reasons we do not recommend the use of chlorine as a disinfec- tant. Some states are currently passing legislation preventing the use of chlorine as a disinfectant in both wastewater and freshwater applications. This is done for reasons of health for both the environment and living creatures. A simplified explanation of the reasoning follows: In order to ensure that enough chlorine has been applied to achieve a maximum pathogen kill, there must be a measurable amount of chlorine in the system discharge. In the case of water- body discharge, this small amount is deadly to virtually all-natural life forms in the water. In the case of land-surface discharge, over a period of time chlorine will build up to a level high enough to cause conversion of soil-bound minerals to salts, which are not only toxic to the soil but will leach out into groundwater supplies. These conversions are expressed as: Cl -r Na NaCl Cl+K KCl Cl+ Mg MgC12 Cl +Ca — CaCl2 In addition, the factors that affect the bacterial and virucidal efficiency of chlorine can vary widely on a seasonal basis from day to day and from daytime to nighttime. In fact,marked varia- tions have been shown in samples taken from the same effluent stream at intervals as short as one hour. The source of chlorine may take many forms. The important thing to remember is that chlorine derived from almost any source forms hypochlorous acid in dilute solutions used for wastewater disinfection. Hypochlorous acid is an extremely potent germicide at pH levels between 6.5 and 7.5, which covers most wastewater applications. However, it is also a highly active oxidizing agent and is therefore short-lived as it reacts with ammonia to form chloramines as: NH3+HOCI NrH.Cl (monochloramine)-+ H2O NH 20 +HOCI NHC, (dichloramine)+H2O NHCI 2+HOCI —► NC13 (nitrogen trichloride)+ H2O These reactions are extremely important, as the disinfecting power of a unit of chlorine as hy- pochlorous acid is between 25 to 100 times as great as that of a unit of chlorine as monochloramine. If the effluent has not gone through a quality nitrification/denitrification proc- -7 7•H Technical Services Group, Ina I