Sludge is a product separated from urban sewage treatment, with a moisture content of over 85% in a flowing state, 65% to 85% in a plastic state, and below 60% in a solid state.

1、Classification of sludge

(1) Classified by source: sedimentation (air flotation) sludge, biological treatment sludge;

(2) Classified by digestion or not: digested sludge (cooked sludge), raw sludge (fresh sludge);

(3) Classification by component: organic sludge, inorganic sludge;

(4) The mixed sludge generated from domestic sewage treatment and the biological treatment sludge generated from industrial wastewater are typical organic sludge, with properties such as easy decay and odor, fine particles, small specific gravity, high moisture content, and difficulty in dehydration.

2、Application of sludge with different moisture contents

When the moisture content of sludge is 10%, it is convenient for storage and transportation. Even if there are active bacteria in the sludge, they are generally not activated and are not easily invaded by bacteria, viruses, fungi, etc. in the air, which can utilize the nutrients in the sludge to reproduce. At the same time, if the moisture content of sludge is low, its heat is high. For example, sludge used for power generation or cement burning is a true energy resource. When drying, it is required that the moisture content of the sludge is too low. On the one hand, it consumes more energy, and on the other hand, after drying, the sludge will also absorb moisture from the air to reach an equilibrium point under certain temperature and humidity conditions, which is even less valuable.

As for incineration, 50% is required because it requires the heat required to evaporate half of the moisture during incineration. The heat generated by burning the organic matter in the remaining half of the dry sludge is sufficient to provide it. At the same time, sludge with a 50% moisture content is more easily dispersed in shape, which is conducive to combustion. It should be noted that sludge with a 50% moisture content is only a minimum requirement.

When the sludge with a moisture content of 60% is buried, its strength can basically meet the compaction requirements and it is not easy to form swamps. Secondly, sludge with a moisture content of 80% becomes sludge with a moisture content of 60%, reducing its weight by half and extending the lifespan of the landfill site. Of course, this is also a minimum condition. The lower the moisture content in landfill, the better. However, it is not worth using drying to reduce the moisture content and achieve a lower moisture content for landfill.

60% moisture content sludge is used for agriculture (referring to fermentation and fertilizer production), based on the need to create favorable conditions for microbial growth during sludge fermentation. We know that this is mainly related to temperature and moisture. Can air be smoothly provided to sludge during aerobic fermentation (porosity of sludge, porosity of sludge pile). Different microorganisms use different methods to ferment sludge with different organic matter contents, and the optimal sludge moisture required is not consistent, generally below 60%; But by no means the lower the better. In addition, during aerobic fermentation, the sludge has a moisture content of 60% and has become solid, making it easier for air to enter.

3、 Rapid detection method for sludge moisture content

In the past, the determination of sludge moisture content was generally carried out using the traditional weight method, which calculates the sludge moisture content from the ratio of the dried weight of sludge to the original weight of sludge. This measurement method is time-consuming, inefficient, and cannot truly meet the automation operation requirements of sewage treatment plants. The new sludge moisture content detector adopts a drying method to directly measure the moisture content of sludge, which is simple and time-saving, and has achieved satisfactory results. The sludge moisture content detector adopts the pyrolysis principle (drying weight loss method), and displays the lost moisture content in real time during the testing process. After the drying program is completed, the final measured moisture content value is locked and displayed.