Cost function for the sludge thickener:

The original cost function (A1) for the thickener is as follows:

This function has as variable (x) the diameter of the thickener in feet (ft). To calculate this diameter, a circular structure is considered, therefore:

Where A is the area of the settler. This area is calculated from the sludge that reaches the thickener, of which the greatest influence is from the settler. For these sludges a concentration of 1% (10 mg / L) is considered, and they are treated approximately at the same time that they are collected in the settler. Additionally, a usual surface load of 20 m / d is taken. With this:

And replacing:

This conversion can also be done depending on the solid load like this:

This value is replaced in the original equation to obtain A2.

Additional modifications to this function correspond to the correction of costs per year, with the CCI ENR index of 9547 of the year 2013, to obtain A3. This function, like the others for sludge treatment, does not require B2 factor of the adjustment for elasticity, this since function A3 already considers the influence of water quality on its costs directly.

According to the above, the following is the function obtained:

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