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Soluble BOD5 Cone., g/m3

Figure 20.10 Illustration of the graphical procedure for determining the hydraulic loading required on each stage of a multi-stage RBC to reduce the soluble substrate concentration from to a desired effluent concentration, SSl.

minimize its size. Thus, to start the procedure, an operating line is drawn from the system influent substrate concentration on the abscissa to the limiting SOL on the ordinate. The intersection of that operating line with the rate curve gives the output substrate concentration from stage 1. A tentative decision is then made about the number of additional stages needed and their size. If they are all the same size they will all have the same THL, making the slopes of the operating lines the same for all stages. The graphical procedure is then employed to determine if the tentative design will achieve the effluent quality goal. If it does not, then a new size is selected and the procedure is repeated. The only constraint is that each stage must consist of at least one complete shaft of standard- (9,300 nr) or high-density (13,900 m:) media. The advantage of the graphical procedure is that it is rapid and allows the designer to visualize easily the impact of decisions. The procedure is illustrated in the following example.

Example 20.3.4.1

Data were collected with a single stage RBC pilot plant to determine the treatability of a soluble industrial wastewater. They were used to determine the relationship between the concentration of soluble BOD, and the related substrate flux into the biofilm, J,, which is presented in Figure E20.1. The plotted points represent the data, whereas the curve represents the general relationship between the soluble BOD, flux and the soluble BOD, concentration. The wastewater to be treated has a design llow rate is 1.500 mVday and a soluble BOD, concentra-

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