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Technical Description bacter organisms. These organisms predominate and utilize the dead cells as a carbon source, converting ammonium nitrogen (NH4), as a nutrient base, to nitrite (NO2) through oxidation. A portion of the resulting nitrate (NO3) rises to the surface of the reactor and is reduced prior to reaching the atmosphere. The nitrosomonas are responsible for conversion of ammonium nitrogen to nitrite, which sponsors the rapid nitrobacter conversion to nitrate: NH 4 + 3/2 02 —> 2I-r + H20 + NO2 (1) and a portion of the NO2 is then oxidized to NO3: NO2 + 1/2 02 --> NO2 --> NO-3 (2) The use of microprocessor and computer technology allows modifications of the timing cycle that controls the amount of time the sludge spends in the treatment system. It is this cycle that is re- ferred to as the Mean-Cell-Residence-Time (MCRT), and is a function of the amount of food pro- vided to bacteria in the aeration reactor tank (the food-to-microorganism (F:M ratio)). There are three basic classifications of the activated sludge process that are defined by the 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 BOD5/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 char- acteristics 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 of food available to a large mass of microorganisms at any given time. This is the principal reason for the Bio-Pure system's ability to handle surges in the organic loading without producing a change in efflu- ent quality. Critical design factors are the tank's length-to-width ratio, amount of air introduced, and turbu- lence 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 100% of sludge volume although only 45% is required in order to maintain the aeration solids. To ensure that a Dissolved Oxygen (DO) of 0.5 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 11.5 cubic feet/gallon of wastewater with an additional mixing factor of 1.5 to 2.0 cubic feet per gallon. 9