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MFR-30-'E3 TUE OE,32 3-IEL_ STO--KTCN 4E94 Pe5 ENVQtEX LTD. As wastewater is introduced to the fluidized bed, microorganisms begin to attach themselves to the GAC media and form a film. As the film grows in thickness, it causes each GAC particle to become lighter in overall density, causing the bed to expand further. Since the particles of the lightest density will tend to rise in a fluidized bed, particles found at the top of the bed will tend to have the thickest layer of biomass. A growth control mechanism, located at the top of the bed, can limit bed height by separating biomass from GAC particles, discharging the biomass, and returning the GAC particles (now denser) to the bed, where they will tend to sink. 2.2.2 Stoichiometry The organisms contained in the GAC-Fluid Bed system are aerobic, and as such, require oxygen in order to carry out their metabolic activities. A general expression for the overall reaction is as follows: Organic Matter + Nutrients + % ----> CO2 + H2O + Cells In this process, the bulk of the organic material is converted into CO2 and H2O, while a small fraction of the organic matter is converted into new cell matter. The amount of oxygen required for the reaction is a function of the amount of organic matter which must be oxidized and the amount of biomass contained in the reactor. The amount of oxygen required by the biomass can be represented by the following equation: 02 — a (CODin - CODd + b' (Xv) where: 02 Amount of oxygen required (lbs./day) COD;, - COD„a - Amount of organic matter removed expressed in COD (lbs./day) Xv Amount of biomass in the process (lbs.) a' % utilization coefficient for cell synthesis (0.7 to 0.8) b' = 02 utilization rate for endogenous* respiration (0.03 to 0.09day) 'Endogenous respiration' is oxygen usage when microbes use Page 2-7