Water is an important material basis for human survival and social development, is a limited, irreplaceable and valuable resources, but also to achieve sustainable economic and social development is an important guarantee. Urban water supply and drainage, including sewage treatment and other infrastructure, is the basic material conditions indispensable to urban production and people's lives, but also an important part of the city's economic development and environmental construction.
In recent years, the Chinese government has adopted a positive financial policy to increase the construction of infrastructure, including urban water supply and drainage, so that China's urban water supply and drainage, especially the construction of sewage treatment facilities has been rapid development, the level of urban water supply and sewage treatment capacity has been a substantial improvement and growth.
China is a country with scarce water resources per capita, listed as one of the world's thirteen water-poor countries. At the same time, China's sewage treatment capacity is poor, the status quo of serious pollution of water resources and further aggravate the problem of water shortage in China. Therefore, whether to enhance China's sewage treatment capacity as soon as possible, effectively curbing the pollution of water resources is the most urgent and effective way to alleviate the shortage of water resources. Due to the scarcity of water resources and sewage discharges continue to grow, the sewage treatment industry in the national economy has an indispensable and important position, the industry will also play an increasingly important role in the national economy.
(II) Classification of sewage treatment industry
Categorized by the source of sewage, sewage treatment is generally divided into production sewage treatment and domestic sewage treatment. Production wastewater includes industrial wastewater, agricultural wastewater, and medical wastewater, etc., while domestic wastewater is the wastewater produced by daily life. Sewage treatment is widely used in construction, transportation, energy, petrochemicals, environmental protection, urban landscape, medical, food and beverage and other fields, but also more and more into the daily life of ordinary people. Modern sewage treatment technology, according to the degree of treatment, can be divided into primary, secondary and tertiary treatment.
Primary treatment, the main removal of sewage in a suspended state of solid pollutants, most of the physical treatment method can only complete the requirements of primary treatment. After primary treatment of sewage, BOD can generally remove about 30%, not up to the discharge standard. Primary treatment belongs to the pretreatment of secondary treatment.
Secondary treatment, the main removal of sewage in the colloidal and dissolved organic pollutants (BOD, COD substances), the removal rate of 90% or more, so that organic pollutants to meet the discharge standards.
Tertiary treatment, further treatment of difficult to degrade organic matter, nitrogen and phosphorus can lead to eutrophication of the water body, such as soluble inorganic substances. The main methods are biological denitrification and phosphorus removal, coagulation and precipitation method, sand rate method, activated carbon adsorption method, ion exchange method and electro-osmosis analysis method.