Views: 9 Author: Site Editor Publish Time: 2018-11-06 Origin: Site
As environmental protection service personnel, how much do we know about sludge? Here, we will carry out research and discussion on sludge to help everyone understand the knowledge of sludge.
What is sludge?
In wastewater treatment, a considerable amount of suspended substances is usually intercepted. These substances are collectively referred to sludge solids, and the mixtures with water are called sludge.
Characters of sludge
Sludge contains a large number of toxic and harmful substances, such as parasite eggs, pathogenic microorganisms, bacteria, synthetic organic matter and heavy metal ions.
Plant nutrients (nitrogen, phosphorus, potassium), organic matter and moisture, etc.
Sludge is a hydrophilic substance with colloidal structure, which is easy to decompose and odor. Because of fine particles and low relative density (about 1.02-1.006), it has high moisture content and is difficult to dehydrate.
Classification of sludge
According to the separation process of sludge from water, it can be divided into sedimentation sludge and biological treatment sludge.
Nowadays, most of the sludge produced in sewage treatment plant is a mixture of sedimentation sludge and biological treatment sludge.
According to the composition and properties of sludge, it can be divided into organic sludge and inorganic sludge.
Organic sludge with organic matter as its main component can be referred to as sludge. Its main characteristics are high content of organic matter, easy to decay and odor, fine particles, small density, high moisture content and difficult to dehydrate. It is a hydrophilic substance with colloidal structure and is easy to be transported by pipeline. Domestic sewage sludge or mixed sewage sludge belong to organic sludge.
Inorganic sludge with inorganic substances as the main component is often called sediment. The characteristics of sediment are coarse particles, high density, low moisture content and easy to dehydrate, but poor fluidity, and difficult to be transported by pipeline. Sediments in the physical and chemical treatment of some industrial wastewater belong to inorganic sludge, and it is generally hydrophobic sludge.
More commonly, sludge is classified and named according to different treatment stages: raw sludge, concentrated sludge, digested sludge, dewatered sludge, dried sludge and sludge incineration ash.
Properties of sludge
The total solids in sludge include two parts: dissolved substances and insoluble substances. The former is called dissolved solid. Total solids, dissolved solids and suspended solids are respectively divided into stable and volatile solids.
Volatile solids refer to those solids that can be oxidized at 600 C and escaped by gas products. They are usually used to indicate the organic content in sludge. The solid concentration of sludge is usually expressed by mg/L, and also expressed by weight percentage %.
Water content means the percentage of water in sludge.
Relative density of sludge
The relative density of sludge refers to the ratio of the weight of sludge to the weight of the same volume of water. The relative density of sludge mainly depends on the water content of sludge and the specific gravity of solids. The larger the relative density of solid is, the lower the water content will be, and the greater the proportion of sludge will be.
The relative density of domestic sludge is generally close to 1. The relative density of industrial sludge is always larger, for example, the relative density of iron slag is 5~6.
Content of heavy metal ions in sewage sludge
The contents of heavy metal ions in sludge are generally high. Therefore, when sludge is used as fertilizer, we must pay attention to whether the content of heavy metal ions in the sludge exceeds the standard.
After introducing so much knowledge about sludge, I believe you know more about it. In the next chapter, we will introduce sludge treatment, in which we will introduce several commonly used sludge dewatering products, such as volute screw press dewatering machine, belt filter press, and other kinds of sludge dewatering machines.