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r Technical Description V to as the mean-cell-residence-time (MCRT), and is a function of the amount of food provided to bacteria in the aeration reactor tank (the food-to-microorganism [F:M] ratio). "^ There are three basic classifications of the activated sludge process which are defined by the process loading range to the microorganisms:high,conventional,and low.The following shows typical ranges of the MCRT and F:M for each loading range: MCRT, F:M Process day lbs BOD/day/lb MLVSS High Rate 3-5 0.4-1.5 Conventional Rate 5-15 0.2-0.4 Low Rate 15-30 0.5-0.2 (Note. lbs/day x 0.01157 =g/kg) In the complete-mix, activated-sludge process, the characteristics of the mixed liquor are similar throughout the aeration tank. That is, the influent waste is rapidly distributed, and operating �. characteristics measured in terms of solids, oxygen uptake rate (OUR), MLSS, and soluble BOD concentration are nearly identical throughout the tank,with a very low level offood available to a large mass of microorganisms at any given time. This is the principal reason far the Bio-Pure system's ability to handle surges in the organic loading without producing a change in effluent quality. Critical design factors are the tank's length-to-width ratio, amount of air introduced, and turbulence �.. throughout the tank. The system is operated at Water Pollution Control Federation and federal EPA design standards, which recommend an MLSS of about 3,000 to 6,000 mg/L. The quantity of sludge returning from the clarifier is 66% of design batch. This percentage is required in order to maintain the aeration solids. To ensure that a dissolved oxygen(DO)of 0.05 ppm minimum exists at all points, a minimum oxygen input of 2.0 mg/L is maintained at the effluent end of the aeration chamber. Therefore, air is supplied at a rate of 0.8 to 115 cubic feet/gallon of wastewater with an additional mixing factor of 1.5 to 2.0 cubic feet per gallon. For sizing the air delivery system, the cubic-feet-of-air requirement is expressed as cubic feet of air required per pound of BOD removed from the aeration reactor. The minimum air/organic loading 06. recommended by most state agencies is 1,000 cubic feet per pound of BOD. The Bio-Pure system expands this to 1,500 cubic feet per pound ofBOD removed,allowing a residual airbase for compensation ofhigher organic loadings than anticipated and to support further processing of ammonium nitrogen(NH).Air availability is always maintained at 125%ofmaximum demand with the 25%residual over the 1,500 CFM injected,bled offbetween the compressor and the aeration tank. Because the total daily air requirement is dependent upon the pounds of BOD applied, the pounds of BOD entering the treatment plant must be known and can be calculated as follows: �' 10