Industrial wastewater: Industrial wastewater discharged directly without treatment is an important pollution source of water, which has the characteristics of large quantity, wide range, complex composition, high toxicity and difficult purification treatment. Industrial wastewater is most common in chemical industry, paper industry, food processing industry, metal products industry, iron and steel industry and leather printing and dyeing industry. Every year, about13 of industrial wastewater in China is directly discharged into water without treatment, and the illegal discharge is very serious.
For example, in Jiamusi City, Heilongjiang Province, industrial and mining enterprises alone directly discharge more than 65.438+million tons of river wastewater every year, and the annual dumping amount of industrial waste residue and domestic garbage exceeds 6.5438+0.4 million tons, among which nitro compounds and phenols in chemical waste residue seriously pollute the groundwater in the urban area and surrounding areas, and the pollutant content exceeds the standard by hundreds of times. Among them, the concentration of phenol in running water, the largest water source in the city, exceeded the standard by as much as 390 times, resulting in water source scrapping and direct economic losses of more than 400,000 yuan. Groundwater is in agricultural areas, mainly nitrate water; In the chemical and pesticide distribution area, it is sulfate water; In densely populated areas, mainly chlorine water. In recent years, chlorine and nitrate have the fastest growth, followed by sulfate. The detection rate of nitrate reached 93? 4%, the over-standard rate is 60? 5%; The detection rate of nitrite was 8 1? 0%; The detection rate of ammonium is 1 1? 0%; Iron 0? 3—33? 0 mg/l, the over-standard rate is 95? 4%。
In June 5438+February 65438+May, 2005, Guangdong Provincial Environmental Protection Department found that the heavy metal cadmium in Shaoguan section of Beijiang River in Guangdong Province exceeded the standard. In the Gaoqiao section of Beijiang River, the monitoring department measured that cadmium exceeded the standard by nearly 10 times, which seriously threatened the safety of drinking water sources downstream. After investigation by Guangdong Environmental Protection Bureau, it was preliminarily confirmed that the pollution incident was caused by excessive discharge of cadmium-containing wastewater during equipment maintenance in Shaoguan Smelter. On February 20th, 65438, the Guangdong provincial government announced this serious environmental pollution accident. Drinking water in Shaoguan, Qingyuan and Yingde in the lower reaches of Beijiang River is threatened by pollution, and tap water supply in some cities has stopped.
Domestic sewage: mainly various detergents and sewage, garbage and feces used in urban life. Domestic sewage contains more nitrogen, phosphorus, sulfur, organic fiber, starch, sugar, fat, protein, urea and pathogenic bacteria. About 90% of domestic sewage in China is directly discharged into the waters without treatment every year.
According to a survey report of the former Environmental Protection Administration, in recent years, the urban domestic sewage discharge in China has increased by 5% annually, and the domestic sewage discharge in China is1840,000 tons in 1998. During the period of 1999, the discharge of urban domestic sewage exceeded that of industrial sewage for the first time, accounting for 52? 9%; In 2003, the total discharge of industrial wastewater and urban domestic sewage in China was 46 billion tons, of which the discharge of urban domestic sewage was 247? 600 million tons, accounting for 5.3? 8%。
For example, Taiyuan City, Shanxi Province, the city's annual wastewater discharge is 1? 900 million cubic meters, and about 65.438+0.9 million tons of various toxic substances are discharged with wastewater every year. Phenol, cyanide, arsenic, mercury and hexavalent chromium in the water of Taiyuan section of Fenhe River are all toxic, and the content of phenol exceeds the drinking standard by more than 2000 times.
Agricultural sewage: including livestock manure, pesticides, fertilizers, etc. In agricultural sewage, first, the content of organic matter, plant nutrients and pathogenic microorganisms is high; Second, the content of pesticides and fertilizers is high. At present, China has not carried out agricultural monitoring. According to relevant data, 654.38 billion hectares of cultivated land and 2.2 million hectares of grassland use pesticides every year. 490,000 tons. China is one of the countries with the most serious soil erosion in the world. The annual topsoil loss is about 5 billion tons, which leads to a large number of pesticides and fertilizers flowing into rivers, lakes and reservoirs with topsoil. With the loss of nutrients such as nitrogen, phosphorus and potassium, two-thirds of lakes are polluted by eutrophication in different degrees, which causes abnormal reproduction of algae and other organisms, changes in water transparency and dissolved oxygen, and thus deteriorates water quality.
Mine waste residue: the waste residue generated by mining pollutes rivers, soil and groundwater after being washed by rain. In particular, the slag of rare metal and heavy metal mines was washed away by rain, which made the heavy metal content in the water exceed the standard.
Air pollutants: Air pollutants can fall into rivers, lakes and oceans and pollute water bodies through precipitation of rainwater.