Slamavvanning

Slamavvanning, often translated as sludge dewatering, is a unit operation in wastewater treatment that concentrates sludge by removing a large portion of its free water. It follows sludge thickening and conditioning and aims to produce a stable, transportable cake with higher dry solids content than the feed material.

The main mechanical methods are centrifugation, belt filter presses, screw presses, and plate and frame filter presses. Gravity drainage is limited and rarely used alone for municipal sludges. The choice depends on sludge type, desired dryness, throughput, and capital and operating costs.

Dewatering usually requires conditioning with chemical aids such as polymers and coagulants, pH adjustment, or lime addition to improve flocculation and water release. Energy use is highest for centrifuges, while belt presses and screw presses use moderate energy. Chemical costs can be significant.

Typical dewatered cake moisture content ranges from roughly 15 to 40 percent dry solids, depending on equipment and sludge characteristics. Centrifuges and filter presses typically produce drier cake than simple gravity drainage. The process also reduces haulage volume and prepares sludge for disposal, incineration, or beneficial use.

In municipal and industrial facilities, slamavvanning is an essential step before disposal or resource recovery. Operators monitor dry solids content, filtrate clarity, polymer consumption, and equipment wear to optimize performance and minimize costs and environmental impact.