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Secondary waste treatment is based on aerobic bacterial activity. Two fractions are involved, soluble,

and insoluble organic matter. The basis of this study was to ascertain whether the major portion of

bacterial activity was a function of specifically located aeration tank sites, of limited volume, or

required the total aerated capacity and the longer detention times. To distinguish between these two

possibilities, an aeration tank was partitioned into hypothetical subvolumes adjacent to the influent

ports. These are the initial respiratory spaces, constituting the initial respiratory phase of secondary

treatment. The remainder of the aerated systems activity occurs in the residual respiratory space or

phase.

Secondary wastewater treatment is the second stage of wastewater treatment that takes place afterthe primary treatment process. The process consists of removing or reducing contaminants orgrowths that are left in the wastewater from the primary treatment process. Usually biologicaltreatment is used to treat wastewater in this step because it is the most effective type of treatmenton bacteria, or contaminant, growth.econdary treatment processes can remove up to 90 percent of the organic matter in wastewater by using biological treatment processes. The

two most common conventional methods used to achieve secondary treatment are attached growth processes and suspended growth

processes.

Siemens is a world leader in all types of biological treatment systems, including some of the most innovative processes in the market

designed to save cost and conserve space and energy:

Secondary Treatment begins with the activated sludge process. The aeration tanks are where bacteriaare grown and cultured. These bacteria use oxygen and feed on the remaining suspended and dissolvedorganic matter from the primary clarifiers.

Air is introduced into the liquid/biological mixture (mixed liquor), by large mechanical mixers (think of ahome batter electric mixer) to assure enough air is in the wastewater for the bacteria to thrive. Toensure enough bacteria are available to consume this waste product, sludge must be returned to the tankfrom the secondary clarifiers (returned activated sludge).

The activated sludge will constantly increase in quantity as it eats more organic material in the

wastewater. When there are too many bacteria it becomes necessary to remove the excess quantityfrom the system. The excess microbiological life removed is termed waste activated sludge and ispumped to tanks called sludge thickeners. All of the return and activated sludge is collected in thebottom of the secondary clarifiers.

Secondary Clarifier - The secondary clarifiers are another set of circular tanks where the bacteria fromthe activated sludge tanks are settled out by gravity. Manchester has three clarifiers where the mixedliquor suspended solids (MLSS) is separated from the clean overflow. The MLSS settles to the bottom ofthe clarifier, is collected by a series of spiral blades and sludge intake ports along the bottom of the tankabd the center column and is either wasted to the thickener(s) or returned back to aeration tanks tomaintain the biological population.

The size of each of the three (3) secondary clarifiers is 145 feet in diameter x 12 feet deep. This

provides a volume of 198,060 cubic feet which is 1,481,489 gallons.

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