Sludge drying

A further reduction of the sludge weight is possible with the help of sludge drying, by evaporating the remaining bound water in the sludge. However a significant reduction of the sludge volume cannot be reached with that method.

Sludge drying procedures are based particularly on contact-, convection or radiation procedures.
Large amounts of air are not necessary during the contact drying, because the warmth is supplied by the contact between the damp product and a heated wall. Only a minimum gas flow is often planned for the evacuation of steam. That has the advantage that the expenditure for exhaust air purification is small.

Convection drying obtains its effect by treating the sludge with hot-air. In addition ambient air is heated to a high temperature with a burner or steam heat exchanger and brought in contact with the sludge in a drum or belt dryer.

The obvious characteristic of radiation drying is that the warmth, which is necessary for the drying process, is supplied through radiation to the sludge. General examples for warmth supply through radiation are solar radiation or infrared heating elements.

For the choosing the suitable drying method one should pay attention to

· Adherence to security
· Environmental compatibility
· Flexibility of the drying method in relation to variable sludge quantities

Because of their high investment and operating costs, sludge drying is mainly used in large wastewater treatment plants.

More information about sludge treatment and reduction are on the following pages:

Stabilisation
Thickening
Dewatering
Copious growth of filamentous organisms - problems and solutions
Filter presses for sludge treatment

Centrifugation and centrifuges