Commonly used activated carbon decontamination techniques in water treatment industry

1. Activated sludge method.

Municipal domestic sewage is mostly treated by the activated sludge method, which is the most widely used biological treatment process in the world. It has the advantages of high treatment capacity and good effluent quality. This method mainly consists of an aeration tank, a sedimentation tank, a sludge return and a residual sludge discharge system. Wastewater and the returned activated sludge enter the aeration tank together to form a mixed liquid. The aeration tank is a bioreactor. Air is filled into the aeration equipment, and the oxygen in the air dissolves into the mixed liquid to produce aerobic metabolic reactions, and the mixed liquid is sufficiently stirred and suspended. In this way, the organic matter and oxygen in the wastewater can fully contact and react with the microorganisms. Then the mixed liquid enters the sedimentation tank, and the suspended solids in the mixed liquid settle in the sedimentation tank and separate from the water. The purified water flows out of the sedimentation tank. Most of the sludge in the sedimentation tank is returned, which is called return sludge. The purpose of the return sludge is to maintain a certain suspended solid concentration in the aeration tank, that is, to maintain a certain microbial concentration. The biochemical reaction in the aeration tank causes the proliferation of microorganisms. The proliferated microorganisms are usually removed from the sedimentation tank to maintain the stable operation of the activated sludge system. This part of the sludge is called residual sludge. In addition to the ability to oxidize and decompose organic matter, activated sludge must also have good coagulation and sedimentation properties so that the activated sludge can be separated from the mixed liquid to obtain clear effluent.

Since sewage treatment is a project that focuses on environmental and social benefits, it is often restricted by funds during construction and actual operation, making treatment technology and funding issues the "bottleneck" of water pollution control in my country. In summary, the current common problems in the research and application of urban domestic sewage treatment are:

1. The use of traditional activated sludge method often has high capital construction and operating costs, high energy consumption, complex management, and sludge swelling; the equipment cannot meet the requirements of high efficiency and low consumption.

2. With the increasingly stringent sewage discharge standards, the discharge requirements for nutrients such as nitrogen and phosphorus in sewage are relatively high. Traditional sewage treatment processes with denitrification and phosphorus removal functions are mainly based on activated sludge methods, which often require multiple anaerobic and aerobic reaction tanks to be connected in series to form multi-stage reaction tanks. The purpose of denitrification and phosphorus removal is achieved by increasing internal circulation, which is bound to increase the cost and energy consumption of infrastructure investment and make operation and management more complicated.

3. At present, the treatment of urban sewage is mainly centralized. The investment in the huge sewage collection system far exceeds the investment in the sewage treatment plant itself. Therefore, building a large sewage treatment plant to centrally treat domestic sewage is not necessarily the only desirable solution from the perspective of sewage regeneration and reuse.

Therefore, how to make the urban sewage treatment process develop in the direction of low energy consumption, high efficiency, less residual sludge, the most convenient operation and management, and the realization of phosphorus recovery and treated water reuse has become a common concern in the current water treatment technology research and application fields. This requires that sewage treatment should not only meet the single water quality improvement, but also consider the resource and energy issues of sewage and the pollutants it contains, and the technology used must be based on low energy consumption and less resource loss.

2. Biofilm method.

In the development and application of sewage biological treatment, activated sludge and biofilm methods have always dominated. The biofilm method is mainly used to remove soluble organic pollutants from wastewater. The main feature is that microorganisms attach to the surface of the medium "filter material" to form a biofilm. After the sewage contacts the biofilm, the dissolved organic pollutants are adsorbed by microorganisms and converted into H2O, CO2, NH3 and microbial cell substances, and the sewage is purified. The required oxidation generally comes directly from the atmosphere. The biofilm treatment system is suitable for treating small and medium-sized urban wastewater. The treatment structures used are high-load biofilters and biorotating discs. Biofilters are more suitable in southern my country. With the development of new fillers and the continuous improvement of supporting technologies, the biofilm treatment process developed in parallel with the activated sludge method has developed rapidly in recent years. The biofilm method is highly competitive in treatment due to its advantages of high treatment efficiency, good impact load resistance, low sludge production, small footprint, and easy operation and management.

3. Oxidation method

Oxidation method is one of the most widely used and promising pretreatment methods for urban domestic sewage. According to the type of oxidant and the type of reactor, oxidation method can be divided into chemical oxidation method, catalytic oxidation method, (catalytic) wet oxidation method, photocatalytic oxidation method, supercritical oxidation method, etc. Although the chemical oxidation method is simple to operate, its treatment effect is not very ideal, and its operating cost is high. Therefore, it is not widely used in urban domestic sewage treatment applications. In order to achieve the purpose of improving treatment effect and reducing operating costs, people have developed some other oxidation technologies. The photocatalytic oxidation method has simple equipment, mild operating conditions, strong oxidation ability, strong bactericidal effect, and thorough treatment. Therefore, it has excellent application prospects in the deep treatment of water and the treatment of difficult-to-biodegrade organic wastewater. It has become a very active research topic at home and abroad. Some experts predict that oxidation method will become one of the important methods for wastewater treatment in the 21st century.