Within the sludge handling process, sludge thickening is an important step that not only minimizes the load of downstream processes but also reduces treatment costs. The main aim of sludge thickening is to separate the water from the solids - thickening the solids content. This can be done in a variety of ways which are listed below.
The most common way of sludge thickening is through the simple use of gravity thickening. Sludge sits in a tank and is allowed to settle at the bottom over time. The clarified water at the top with minimal solids content is removed from the tank and the sludge at the bottom is collected then removed.
Dissolved air flotation produces tiny air bubbles that cause the solids to float to the surface. The solids are then skimmed off the top. This method is usually used for sludge that takes awhile to settle.
Another method is Centrifugation. This method uses centrifugal force to separate the solids from liquid. The sludge goes into a bowl that spins at a rapid rate causing the solids to settle on the walls of the bowl. The water then drains out and the solids can be scraped from the sides of the bowl.
Image of Rotary Drum Thickener
Rotary Drum Thickening is similar to centrifugation except the drum spins at a much slower rate. The solids get stuck on ridges on the inside of the drum while the water gets drained out through the tiny pores that line the drum.
Belt Filter Presses are also used to thicken sludge. Sludge is fed onto a porous belt that allows water to drain while keeping sludge on the belt. The sludge is compressed by rollers that sit at a certain height above the belt, essentially squeezing the water out and leaving the sludge behind.
Sludge thickening is crucial because it minimizes the disposal cost and makes digestion and dewatering - processes that follow thickening - easier.
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