We have removed solids at various points in the wastewater treatment process: primary sludge composed of the sewage solids collected in the primary clarifier and waste activated sludge from the secondary clarifier.

This sludge presents two problems. First, it is rich in organic matter and will consume oxygen and create foul odors if delivered to the environment without further treatment. Second, even though it's called sludge, it is mostly water and is difficult to handle in final disposal.

Thus sludge processing involves two steps:

• digestion - to break down the organic matter

• dewatering - to reduce the water content and make it easily handled

The treated sludge is then sent on for final disposal.