Difficulties and harm of industrial sludge treatment
Sludge refers to solid, semi-solid and liquid waste substance generated in the treatment of sewage water, which contains much organic, nutrients with rich nitrogen and phosphorous, heavy metal and pathogenic bacteria. If we randomly discharge and pour the sludge without any treatment, it will cause serious pollution:
* It will occupy and erode the land;
* It will pollute soil. The composting sludge will cause harmful components to assemble and be exposed to the open air. So under the condition of high temperature or other chemical reactions, the harmful components will kill the soil microorganism and destroy its structure, which must lead to the lose of decomposing ability;
* Sludge is often poured into river directly, which will pollute the river water;
* Sludge is also harmful to the air. The organic of sludge will be decomposed by microorganisms to release harmful gases and dust, which has further polluted the air;
* The pathogen includes the intestinal bacteria, parasites and viruses, and most are concentrated in the sludge particles, which has seriously threatened the humans’ health.
Principles of sludge treatment and disposal
Reduction, stabilization, harmless, resource-based.
Advantages and disadvantages of sludge disposal methods
The methods of sludge treatment include: healthy landfill, incineration, made into bricks directly, used as fertilizer and sludge carbonation or pyrolysis. The advantages and disadvantages of several disposal methods are as follows:
|Healthy landfill||After dried, sludge mixed with living waste is sent to landfills.||Low investment, need not to install other equipment.||Low stability of sludge will make it rotted to generate odor, and the moisture of sludge will permeate, which will pollute the underground water. In addition, the cost of landfills will also increase year by year.|
|Incineration||Utilizing high temperature for oxidation combustion reaction. Under the condition of excess air, all the organic and pathogen in the sludge will be destroyed through the oxidation and pyrolysis with the temperature of 850 to 1100 degree centigrade.||Small occupation area, fast processing, large handing capacities; what’s more, the residual material can be sent to landfill or used as the constructional materials or paving accorduing to the content of heavy metal.||Large investment, and we need to install the specialized incineration with high maintenance cost; it will generate Dioxin and other highly toxic substances.|
|Directly made into bricks||Dried sludge mixed with clay in the appropriate proportion to fire.||Realize the resource-based of sludge, which has an excellent social benefits. In the operation process, the heavy and harmful metal will be sealed in the bricks so as to can kill the harmful germs. Sludge brick is light with many hole, so it has a well sound insulation and thermal insulation effect.||The sludge source is unstable, and the high water content causes the large consumption with low burning quality. When firing, the whole process is accompanied by malodorous gases and toxic and harmful gases.|
|Used as fertilizer||By adding a certain proportion of bulking agent and conditioner in the sludge, the organic matter is oxidized and decomposed by microorganism, and finally converted into a kind of humic acid with higher stability.||Making the sludge resource utilized.||It needs a high temperature treatment to be made into fertilizer. It also needs to add a follow-up processing equipment such as turning machine. It also needs a large field. In addition, the sludge fertilizer must meet the related standards.|
|Carbonization of sludge||Utilizing the instability of organic in the sludge, and heating under the condition of no oxygen, the hydrocarbon organic matter is carbonized to generate gas phase (pyrolysis gas), and solid (solid residue, charcoal).||High energy utilization, high capacity reduction, low operating costs; no dioxin, furan and other harmful gases; renewable energy recovery.||Require a certain amount of capital investment and technical support.|
Carbonation of sewage sludge
1. The operation flows of sludge carbonization:
The sludge and a part of dried sludge are mixed in a blender and dried in a desiccator and then fed into the carbonization furnace; The gas coming out from the dryer will contract through the condensation system in the cooling tower, used as combustion gas in the combustion chamber; the gas produced by carbonization process can be recovered into heat source; the gas is introduced into the combustion chamber to burn in the high temperature of above 800 DEGC, and the high temperature gas generated in the combustion chamber is used for drying to generate steam in the waste heat boiler; the fuel can be added in the combustion chamber when the energy is insufficient.
2. The advantages of the sludge carbonization technology:
The carbonation technology of sludge is a promising technology and has been used in a mature way. It can produce valuable gas and solid. The operating system is closed with no pollution emissions. The operation cost is lower than incineration. So, what we can make sure is that this technology has great development prospects, and is a promising method for solid waste treatment.
Compared with landfills, adopting carbonization technology to treat sewage sludge has the advantages of less investment cost, less harmful gas and less energy consumption; its harmless and reduction degree are also high. Although the funds and technical inputs can not be avoided, but due to the recycling of hot gas as a heat source, it has a certain benefit return.