Temperature and Moisture

The temperature increase caused by a predetermined dose of quicklime may be calculated by the formula



= temperature increase of the residual, °C


= quicklime activity factor, typically 0.9


= mass of quicklime, kg


= mass of residual, kg


= specific heat of quicklime = 0.92 kJ/kg • °C


= specific heat of residual in kJ/kg • °C may be calculated as

where WSL is the moisture content (in %) of the dewatered residual.

Raising the residual temperature by 10°C doubles the speed of the microbiological activity that accomplishes the composting process.

The addition of quicklime absorbs moisture from the sludge, thereby reducing the moisture content of the compost mixture. The sludge moisture content after the addition of quicklime can be calculated using the formula

where WK is the moisture content (in decimals) of the sludge after the addition of quicklime. The lowering of the moisture content of the sludge decreases the volume of the sludge. This decreases the amount of quicklime required to raise the pH to 10.5. Therefore, it is reasonable to dewater the residual prior to the addition of quicklime.

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