(I) Industry Status
Water is an important material basis for human survival and social development, a limited and irreplaceable precious resource, and an important guarantee for achieving sustainable economic and social development. Urban water supply and drainage, including sewage treatment and other infrastructure, is an indispensable basic material condition for urban production and people's life, and also an important part of urban economic development and environmental construction.
in recent years, the government of China has adopted a proactive fiscal policy and increased infrastructure construction including urban water supply and drainage, which has made the construction of urban water supply and drainage, especially sewage treatment facilities in China, develop rapidly, and the level of urban water supply and sewage treatment capacity have been greatly improved and increased.
China is a country lacking in water resources per capita and is listed as one of the thirteen water-poor countries in the world. At the same time, the current situation of poor sewage treatment capacity and serious water pollution in China has further aggravated the shortage of water resources in China. Therefore, it is the most urgent and effective way to alleviate the shortage of water resources to strengthen the sewage treatment capacity in China as soon as possible and effectively curb the pollution of water resources. Due to the scarcity of water resources and the increasing sewage discharge, the sewage treatment industry plays an indispensable role in the national economy, and it will also play an increasingly important role in the national economy.
(II) Classification of sewage treatment industry
According to sewage sources, sewage treatment is generally divided into production sewage treatment and domestic sewage treatment. Production sewage includes industrial sewage, agricultural sewage and medical sewage, and domestic sewage is the sewage produced in daily life. Sewage treatment is widely used in construction, transportation, energy, petrochemicals, environmental protection, urban landscape, medical care, catering and other fields, and it has also entered the daily life of ordinary people more and more. Modern sewage treatment technology can be divided into primary, secondary and tertiary treatment according to the degree of treatment.
Primary treatment mainly removes suspended solid pollutants from sewage, and most physical treatment methods can only meet the requirements of primary treatment. After primary treatment, BOD can generally be removed by about 31%, which can not meet the discharge standard. Primary treatment belongs to the pretreatment of secondary treatment.
secondary treatment mainly removes colloidal and dissolved organic pollutants (BOD, COD) in sewage, and the removal rate can reach over 91%, so that the organic pollutants can meet the discharge standards.
Three-stage treatment, further treatment of refractory organic matter, soluble inorganic matter such as nitrogen and phosphorus, which can lead to water eutrophication. The main methods include biological nitrogen and phosphorus removal, coagulation and precipitation, sand ratio, activated carbon adsorption, ion exchange and electroosmosis analysis.