Sludge is a byproduct of many industrial or refining processes. Sludge is mostly water with lesser amounts of solid particles. It has a viscous consistency that is thick, wet, and mud-like.
Thickening is often the first step is treating raw sludge. Thickening is meant to reduce the volume of water in the sludge. It is carried out in a sedimentation tank or pool. Sludge contains toxins. Thickening increases the toxin concentration within the solid particles left behind from the process.
Sludge solids can be treated via anaerobic respiration or incineration. Anaerobic respiration is used to digest sludge in the absence of oxygen via the use of bacteria. Incineration is the burning of the sludge. Incineration of sludge often utilizes hearth incinerators. Anaerobic respiration and incineration of sludge may produce methane gas.
In the presence of oxygen, bacteria may also be used to digest sludge via aerobic respiration. In this process, carbon dioxide is produced.