Solid Handling and Disposal
Solids from the primary clarifier (primary sludge) and secondary clarifier (secondary sludge) contain large volumes of water. This increased amount of water increases the overall volume of sludge that must be handled, increasing the size of the equipment, such as digesters, that must be installed.
To decrease this volume, the sludge can be thickened. Essentially, this results in an increase in the concentration of solids and a decrease in the total volume that must be handled in subsequent processes.