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� Technical Description discharged. A third problem, that of sludge bulking, does not occur in Bio-Pure systems, as settling takes place under quiescent conditions and therefore there is no motion within the clarifier to prevent any filamentous organisms from settling. Bio-Pure plants do not suffer from eitheryofthese problems,as there is no uncontrolled discharge over the weir and there are no moving skimming devices. 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 which remain on the surface of the sludge volume. The entire sludge volume,including the floating solids,is then returned to the aeration chamber by the sludge return pump,which completely empties the clarifier each cycle (14.7 cycles per 24-hour day). After settling has occurred, the microprocessor initiates the supernatant transfer pump(SNT),which transfers the supernatant into the chloririe contact chamber. During the supernatant transit, chlorine is injected into the transfer line. By injecting chlorine directly into the transfer line, short-circuiting (which can take place when chlorine is injected directly into the contact tank) is prevented. Chlorine injection is regulated to give maximum pathogen kill with a minimum residual. NOTE: 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: i . 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 ofwaterbody 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'wilI 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:+Na -4 NaCl Cl i+ K KCI Cl'+Mg MgClz CI'+ Ca CaCl2 In addition,the factors that affect the bacterial and virucidal efficiency of chlorine can varywidely on a seasonal basis from day to day and from daytime to nighttime. In fact, marked variations have been shown in samples taken from the same effluent stream at intervals as short as one hour. i The source of chlorine may take many forms.The important thing to rememberis 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:,