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How to Classify Various Sludges after Sewage Treatment
2019-1-31
Source:Publication
Clicks:  6714        作者:未知
  • Sludge is a by-product of sewage treatment by physical, chemical, physical and chemical methods and biological methods. It is a very complex heterogeneous body composed of organic debris, bacteria, inorganic particles, colloids and so on. The concentration of suspended solids is generally 1%-10%, and it is in a colloidal state between liquid and solid forms.

    Problems Existing in Various Sludges

    1. High water content, the water content of undehydrated sludge is more than 90%, and the water content of preliminary dehydrated sludge is as high as 80%. Transportation cost is high, and the storage area is large. Direct landfill will squeeze the storage capacity of landfill, make landfill scrap ahead of time, and cause blockage of landfill leachate pipe and other problems.

    2. Sludge contains a variety of minerals, and contains more plant nutrients such as nitrogen and phosphorus, and heavy metal ions such as copper, zinc, chromium, mercury and their salts. When sludge is used for land use, if improperly applied, it may pollute the land, cause irreversible degradation of cultivated land, and directly threaten the human food chain. Moreover, these substances will enter surface water or groundwater through surface runoff or precipitation, which will affect the water quality, including nitrogen, phosphorus and even cause eutrophication.

    3. Because of the high content of organic matter, it has a high calorific value. The calorific value after drying is equivalent to that of lignite, but it is easy to corrupt and emit odor, which affects the quality of atmospheric environment.

    4. Sludge contains a large number of parasitic eggs, microorganisms, pathogens and other non-degradable toxic and harmful substances, such as PCBs, dioxins, radionuclides. If directly applied or poorly treated, it will cause serious secondary pollution and even infectious diseases.

    5. Sludge density is small, generally distributed in the range of 1.002-1.006g/cm3, and the particles are fine, between 0.02-0.2mm. It is easy to transport in pipeline, but its dehydration is poor, so it is difficult to separate solid from liquid by sedimentation.

    Classification of various sludges:

    According to source classification: sludge can be roughly divided into three categories: feed water sludge (sludge from raw water purification, such as water works), domestic sewage sludge and industrial wastewater sludge.

    According to the composition and properties of sludge, sludge can be divided into organic sludge and inorganic sludge. Organic sludge is a hydrophilic sludge with organic matter as its main component. Domestic sewage sludge or mixed sewage sludge belong to this category. Inorganic sludge is mainly composed of inorganic substances, often referred to as sediment, generally hydrophobic sludge. This kind of sludge includes sediment in the process of physical and chemical treatment of water supply and some industrial wastewater.

    According to the classification of sludge treatment process, sludge can be divided into primary sludge, surplus sludge, digestive sludge and chemical sludge. Among them, primary sedimentation sludge refers to the sediment produced in the primary treatment of sewage; surplus sludge refers to the activated sludge discharged from the secondary sedimentation tank or sedimentation zone; digested sludge refers to the sludge obtained after aerobic or anaerobic digestion of raw sludge; chemical sludge refers to the sludge produced by chemical enhanced primary treatment or tertiary treatment.

    According to the different stages of sludge production, it can be divided into raw sludge (primary sedimentation tank sludge), concentrated sludge, digested sludge, dewatered and dried sludge. This method is the most commonly used sludge classification method. Among them, raw sludge refers to sediment or suspended matter separated from primary and secondary sedimentation tanks, including primary sedimentation sludge, secondary excess sludge or mixed sludge; concentrated sludge refers to sludge obtained by concentrated treatment; digested sludge refers to sludge obtained by aerobic or anaerobic digestion of raw sludge; dewatered and dried sludge refers to sludge obtained after dewatering and drying treatment; Dry sludge refers to the sludge obtained after drying.
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