Sludge thickeners are essentially used in most wastewater treatment plants for the purpose of increasing concentrated solids and reducing free water inside the process of an activated sludge. While there are many types of processes available for sludge thickening, the most common ones are floatation of dissolved air, thickening of rotary drum and thickening of gravity.

There are several other steps that come after sludge thickening but it is one of the important steps that is not skipped during the wastewater treatment. Continue to read till the end to find out more in details about the role of this process.

What is the “Sludge” in Wastewater Treatment?

Before we discuss the process of sludge thickening, let us first learn about what exactly is the “sludge” in wastewater treatment. Sludge is basically composed of biosolids that are extracted from liquid sewage.

Its origin can be varied and regardless of that sludge contains water, dissolved organic and sometimes inorganic materials along with suspended solids. The suspended solids generally make up 2 to 5 percent of the sludge for the municipal wastewater sludge.

The characteristics of sludge depends upon the original quality of feedwater and the type of the operation unit from which the sludge is eliminated.

What Does Sludge Thickening Do?

The sludge thickening process is an important step as it is used in wastewater treatment plants to maximize the solids concentration and decrease the free water present in the sludge.

This step helps in reducing the load that is suffered by the downstream processes that includes sludge dewatering and digestion.

The Work Mechanism of a Sludge Thickening Device

There are varied processes that go into sludge thickening. Each one relies on the downstream process, the wastewater plant size and the physical limitations that come along with it.

The gravity thickening process involves use of specially engineered circular tanks that does the work of concentrating thin sludges to a denser sludge product. The restriction that is present in this clarification water treatment form is that it operates mostly for the excessive watery sludge resulting from an activated -sludge process.

Thickening tanks often have slow operating vertical paddles. The sludge flows into the thickening tank and ultimately it eliminates the excess water from the solids accumulated at the bottom of the tank. A gravity thickener works similarly to the tanks process; however, it has a sloped design for collecting the solids at its base.

Dissolved air flotation is yet another type of sludge thickening process in which the small air particles stick to the suspended solid material. This type of sludge thickener allows the solids to break down and float to the surface.

The suspended solids have reduced gravity than water when the air bubbles stick to them which helps them to float toward the surface. These small air particles contribute in forming a sludge blanket that can be removed and treated conveniently.

There are more sludge thickener processes that have different working mechanisms than the other. However, the primary purpose remains the same which is to increase solid concentration and reduce free water present in them.