The industrial revolution has brought economic development, meanwhile people have gradually noticed the increasingly serious river pollution. The pollution of the river has gradually affected their work and life. So people have to pay attention to the sewage treatment. Until the 1980s, it was learned that the engineering should conform to the principles of ecology, and proposed the construction of multi-natural rivers and other governance concepts. At present, there are three general methods of river sewage treatment, namely physical methods, chemical methods, ecological-biological methods, ecological methods (including river aeration, reoxygenation, biofilm, bioremediation, land treatment). , aquatic plant purification method).
The physical methods mainly refer to the dredging of sediment, mechanical algae removal, water diversion and water transfer. Dredging the bottom of the pollution means removing the pollutants from the (river) system. The contribution rate of the sediment to the overlying water body can be reduced to a large extent, thereby improving the water quality. The purpose of water diversion is to improve the quality of the downstream polluted rivers by introducing the clean water source upstream or near the polluted river channel through the water conservancy facilities (such as gates and pumping stations). Such methods often do not cure the symptoms.
Chemical methods are including such as coagulation and sedimentation, addition of chemical agents to kill algae, addition of iron salts to promote sedimentation of phosphorus, addition of lime to remove nitrogen and etc.Studies have shown that this method has a good effect on the removal of turbidity, eoD, ss and TP, and also has a certain removal effect on TN and heavy metals. However, the river sewage treatment method is likely to cause secondary pollution.
Ecological-biological methods including river aeration, reoxygenation, biofilm, bioremediation, land treatment, aquatic plant purification method.
Artificial aeration and reoxygenation refers to artificial oxygenation in rivers in anoxic (or anaerobic) state to enhance the self-purification capacity of the river, improve water quality, and improve or restore the ecological environment of the river. River aeration and reoxygenation generally adopt two forms: fixed oxygenation station and mobile oxygenation platform. The process has the advantages of simple equipment, mobile and reliable, less investment, quick effect, convenient operation, wide adaptability and no harm to aquatic ecology, and is suitable for the treatment of urban landscape rivers and micro-polluted source water.
Biofilm technology means that the microbial population is attached to the surface of some carriers and is in the form of a membrane, which is in contact with sewage. The microorganisms on the biofilm take up the organic matter in the sewage as nutrient absorption and assimilate, thereby purifying the sewage. At present, the biofilm technology commonly used in river sewage treatment mainly includes inter-gravel contact oxidation method, contact oxidation method of holding water ditch (channel), bio-activated carbon packed column purification method, thin layer flow method and volt-flow purification method.Contact oxidation method is used more.
Bioremediation technology refers to the engineering technology system that uses microorganisms and other organisms to degrade toxic and harmful pollutants in water or soil into c02 and water, or into non-toxic and harmless substances. There are two main types of bioremediation technologies for river sewage treatment. One type is to directly add one or more microbial strains that have been cultured and screened to the polluted river. The test proves that the removal rate of cOD is more than 90-96%. Another type is to add microbial growth promoters (nutrient substances) to polluted river to promote the microorganisms growth of "indigenous". After putting the medicine,Through the promotion of growth, promote the pollutants degradation and the growth of microorganisms. The microorganisms in the river are replaced by anaerobic to aerobic, the organisms are succeeded from low to high, and the diversity of organisms is increasing, so that the BOD5 and COD of polluted water bodies are rapidly declining. The dissolved oxygen is obviously increased, and the black odor is eliminated. This method has obvious effects on eliminating black odor in water and increasing dissolved oxygen in water.
Land treatment technology
Land treatment technology is an ancient but effective river sewage treatment technology. It uses land as a treatment facility and utilize the adsorption, filtration and purification functions and self-regulation functions of seven soils and plant systems to achieve a certain goal of water purification.Foreign experience shows that the land treatment system has a good removal effect on organic compounds, especially organic chlorine and ammonia nitrogen.
Aquatic plant purification
This method is a sewage purification method that fully utilizes the natural purification function of aquatic plants. For example, duckweed, reeds in wetlands are purified in a certain water area. However, the discharge of domestic sewage will cause problems such as odor, pests and landscape effects. Therefore, when selecting it is necessary to comprehensively consider the above problems, such as in spring and summer selecting to plant reeds in the position of the downwind.