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............._ <br /> Dc V" Poilation 58277 Happy Hollow Rd. Suite 1-B <br /> oiitr k Milford, c)}14515th-1 3{} <br /> ? i '�. Tel: (513) 831-1165, Fax: (51.3) 65-4812 <br /> ---- teinsa E-€-na1l: .F'olcr)nsys(µaoi.cortr <br /> www.Pol I U t I oricon trol SySte! I.C.oil) <br /> Operational Procedures & Factors for Process Control <br /> With Flow Equalization Tanks <br /> All activated sludge wastewater treatment plants, which include package extended <br /> aeration, depend on microorganisms (bacteria) to treat the wastewater. The bacteria <br /> must have sufficient contact time with the wastewater to reduce pollutants in the <br /> wastewater to an acceptable level. For package extended aeration wastewater treatment <br /> plants, the design contact time between the bacteria and the wastewater is 18 to 24 <br /> hours. This contact time and the daily flow determine the size of the aeration chamber, <br /> where oxygen (air) is supplied to the mixture of microorganisms and organic matter in the <br /> wastewater. <br /> A package extended aeration plant is sized to accept the volume of wastewater produced <br /> during a 24-hour period, measured in gallons per day (GPD). A constant flow to the plant <br /> during this period is ideal. The ideal flow rate or average flow rate for the 24-hour period <br /> may be found by dividing the daily flow by 1440 minutes (1 day = 24 hours = 1440 <br /> minutes). Unfortunately, wastewater flows are not constant, but vary during the day. <br /> Water use is highest in the morning as people prepare for work or school, and during the <br /> evening hours. Because a wastewater treatment plant is designed on the 24-hour flow <br /> basis, it is critical that high (peak) flows do not cause sludge to be washed for the plant. If <br /> solids are lost during peak flow periods, then flow equalization may be required. Flow <br /> equalization is a method of temporarily storing wastewater during periods of excessive <br /> flows, then feeding it to the treatment plant uniformly throughout the 24-hour period. <br /> Many regulatory agencies require flow equalization for treatment plants serving schools <br /> and campgrounds. <br /> Problems associated with hydraulic surges (peak flows) can be eliminated by installing an <br /> equalization tank at the influent of the package wastewater treatment plant. Hydraulic <br /> surges flow into the equalization tank and are stored. The wastewater can then be <br /> pumped to the aeration chamber at a uniform rate of flow. Because the flow into the <br /> equalization tank (often referred to as a surge tank) during periods of peak flow will <br /> exceed the pumping rate to the aeration chamber, the liquid level in the equalization tank <br /> will rise. Sufficient storage must be provided in the surge tank to allow for this rise. <br /> Various factors will determine the required storage capacity. These design criteria will <br /> vary depending on the region in which the plant is located. However, not all plants need <br /> equalization tanks. For those plants that do; the volume of the equalization tank may be <br /> from 5 to 60% of the aeration chamber volume. <br /> I pcsl,'O&-tti-proced-precesscontrolw,,Fy-1 <br />