Cost function for sludge drying beds:

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

This function has as variable (x) the area of the beds in square feet (ft2). To calculate this, the sludge produced by the settler and the filter are considered. Both types of sludge are considered to have been previously thickened to a concentration of 5% (50 mg sediment / L sludge). The sludge from the settler is collected every 30 days and is left to dry for 15 days, while those from the filters are collected every 2 days and left to dry for 4 days. Finally, the load that these beds accept is 20 L / m2 / d. With this information we calculate the area like this:

Since there will be a part of the area dedicated to the sludge, from the settlers, while there will be another part dedicated to filter sludge. Then:

Then,

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, since function A3 already considers the influence of water quality on its costs directly

With this, the following the function is obtained:

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