Sludge Treatment and Disposal Technology (8)

36. What Processes Are Involved in Sludge Treatment?

The main purpose of sludge treatment is to reduce water content, create conditions for subsequent treatment, utilization and transportation; eliminate toxic and harmful substances that pollute the environment; recover energy and resources. Sludge treatment processes include sludge concentration, digestion, dewatering, drying and incineration for final treatment.

(1) Sludge concentration. The purpose of sludge concentration is to initially dewater the sludge, reduce the sludge volume, and create conditions for subsequent treatment. Concentration and dewatering methods include gravity sedimentation concentration, floating concentration and other concentration methods.

(2) Sludge digestion. In order to reduce the amount of sludge, prevent environmental pollution and increase its utilization value, it is generally necessary to undergo digestion treatment. Sludge digestion is to use the metabolic action of microorganisms to decompose organic matter into stable substances, remove odor, kill parasite eggs, reduce sludge volume, and recycle the biogas generated during digestion.

(3) Sludge dewatering and drying. After concentration and digestion, its water content is still around 96%. It is very large and not convenient for transportation. It needs further dewatering and drying. The main methods are natural evaporation and mechanical dewatering.

(4) Sludge incineration. After sludge drying, the water content is still 10% to 15%, and the volume is still large. Incineration can completely remove the water and organic impurities in the sludge and kill pathogenic microorganisms. Some sludge contains toxic substances and is not suitable for use as agricultural fertilizer, or is difficult to recycle, this type of sludge can be  disposed of by incineration. The device for incinerating sludge is an incinerator.

(5) Final treatment of sludge. When sludge contains toxic substances such as heavy metal ions, it must be finally treated and landfilled or dumped into the ocean. However, final treatment is rarely carried out, but it can be used at any time during the treatment process.