Sludge is a by-product produced by sewage treatment plants during the treatment of sewage. It is an aggregate formed by suspended matter in microorganisms, microorganisms, organic substances adsorbed by microorganisms, and products of microbial metabolism. It may also contain a large amount of heavy metals and pathogenic bacteria. ,virus.
Although sludge has many kinds of toxic substances, it also has many kinds of available elements, such as a variety of inorganic components: silicon, aluminum, iron, calcium and so on. Improper treatment and disposal will not only cause secondary pollution to the environment, but also cause serious waste of resources.
Sludge treatment and disposal is a process of reducing, stabilizing, harmless, and reusing sludge by reducing, stabilizing, dehydrating, stabilizing, drying, or incineration of the sludge.
The following briefly introduces several common sludge disposal methods, most of which are also the current sludge disposal methods of ecological companies.
I. Use of building materials
1.Ceramics made from sludge
Ceramsite is a kind of ceramic light artificial stone. It is made of clay, mudstone, various shales, coal gangue, fly ash and other main raw materials. It is crushed into pellets or granulated into balls after processing, and then swelled. The resulting artificial light aggregate has the characteristics of low density, high strength, heat insulation, heat insulation and good seismic performance. It is widely used in the fields of building materials, horticulture, refractory and thermal insulation materials, and chemical industry.
The sludge can replace part of the clay and mix with the clay evenly at a certain ratio. After granulation by the granulator, it is sent to a rotary kiln. At high temperatures, the pellets are melted to produce a suitable viscosity and surface tension. Gas, which acts on the molten liquid phase, generates pores and expands. After cooling, the surface is a dense and hard glaze layer, and the inside is a closed porous structure.
2. Blended cement kiln
The main chemical components of sludge and cement raw materials are the same. The "waste heat drying + cement kiln blending" process is used to treat the sludge. The sludge can be used as an auxiliary fuel for the calcination of cement clinker, and can also partially replace clay. Raw materials to reduce the damage of cement production to cultivated land. Utilizing a cement kiln to treat urban sludge, the organic and inorganic components in the sludge can be fully utilized. Organic components will generate heat when calcined in the cement kiln, and the inorganic components will eventually be converted into cement products.
3. Brick made of sludge
Brick is a building material made of clay, shale, coal gangue or fly ash, which is made by molding and high-temperature baking, and is used for building load-bearing and non-load-bearing walls.
The chemical composition of the sludge is similar to that of the clay. After drying, the sludge and clay are mixed with water at a certain ratio, then pressed into a brick module, aged at room temperature, and then fired into bricks. During the firing process, the organic matter in the sludge will also burn to generate heat, which can save coal burning. The heavy metals in the sludge are roasted at high temperature to form a stable solid solution, which will not pollute the environment again.
Anaerobic digestion + drying / incineration
Sludge anaerobic digestion refers to the digestion technology of sludge by facultative bacteria and anaerobic bacteria to decompose biodegradable organic matter into CH4, CO2, H20 and H2S under anaerobic conditions. It can remove 30% ~ 50% of organic matter in the waste and stabilize it.
The sludge anaerobic digestion can decompose the sludge organic matter and generate a large amount of high calorific value biogas. The digested material after the anaerobic digestion is deeply dehydrated by a plate and frame filter press, so that the sludge can be reduced, stabilized, and utilized. .
Compost is generally divided into aerobic compost and anaerobic compost. Aerobic composting is the use of aerobic bacteria and oxygen to subject the sludge to high-temperature fermentation, which thoroughly decomposes the organic harmful substances, and changes the organic matter from an unstable state to a stable humus substance. Its compost product does not contain pathogenic bacteria and contains no impurities. Grass seed, odorless and tasteless, is an excellent soil improver and organic fertilizer.