Causes of water pollution in Xiangjiang River

There are two main reasons for lake water pollution:

1: Natural pollution is due to the change of natural laws and the pollution of water sources by minerals in soil;

2. Man-made pollution. It is the pollution caused by human life and production activities. Generally speaking, water pollution refers to man-made pollution. Including industrial wastewater pollution, agricultural pollution, domestic sewage pollution and water pollution caused by urban domestic garbage.

1, industrial wastewater pollution.

Industrial wastewater includes production wastewater and production sewage, which refers to wastewater and waste liquid generated in industrial production, including industrial raw materials, intermediate products, by-products and pollutants lost with water generated in the production process. Industrial wastewater is the main pollution source of water, which has a wide range, large quantity, many pollutants, complex components, certain toxicity and great difficulty in treatment. For example, wastewater from power and mining sectors mainly contains inorganic pollutants, while industrial sectors such as papermaking, textile, printing and dyeing, and food often discharge a large amount of wastewater with high organic content. BOD5 often exceeds 2,000 mg/L, and some reach 30,000 mg/L. Even in the same production process, the water quality will change greatly, such as oxygen top-blown converter steelmaking and different smelting stages of the same furnace steel. The pH value of wastewater can be between 4 ~ 13, and the suspended matter can be between 250 ~ 25000 mg/L, and the organic matter in these wastewater consumes a lot of dissolved oxygen during degradation, which is easy to cause the water quality to turn black and stink. With the increase of mining and industrial activities, the production and use of heavy metals have also increased greatly, resulting in serious heavy metal pollution in lakes and rivers. Due to the high treatment cost and large investment, industrial wastewater is directly discharged without treatment, or discharged below the standard, which seriously pollutes water resources.

2. Agricultural pollution

Agricultural pollution source refers to the water pollution source caused by agricultural production. Including the use of pesticides and fertilizers, soil erosion and agricultural waste. For example, the unreasonable use of chemical fertilizers and pesticides causes soil pollution, destroys soil structure and soil ecosystem, and then destroys the ecological balance of nature; Runoff and seepage formed by precipitation bring nitrogen, phosphorus, pesticides and organic wastes from pastures, farms and agricultural and sideline products processing plants into the water body, which deteriorates the water quality and causes eutrophication of the water body. With the rapid growth of chemical fertilizer application, soil hardening, poor farming quality, low fertilizer utilization rate, easy loss of soil and fertilizer nutrients, surface water and groundwater pollution. The pollution of pesticides to water bodies is very serious. At present, the total output of pesticides in China has exceeded 400,000 tons, and the number of varieties produced has increased from 5 in 1986 to more than 200. The annual pesticide consumption is about 230,000 tons, and the average pesticide consumption is 2.33 kg/hm? According to the analysis, generally only 10% ~ 20% pesticides are attached to crops, while 80% ~ 90% pesticides are lost in soil, water and air, and the water body is polluted by irrigation water leaching and precipitation. The pollution of chemical fertilizers to water bodies is also very serious. According to statistics, China uses 45.37 million tons of chemical fertilizers and 500,000-600,000 tons of pesticides every year. In the process of agricultural production, the land area using pesticides and fertilizers exceeds 280 million hm? Because surface runoff brings a lot of pollutants into the water body, it is the main source of agricultural polluted water body. And organic wastes from pastures, farms and agricultural and sideline products processing plants are discharged into water bodies, which can worsen the water quality and cause water pollution such as rivers, reservoirs and lakes.

3. Domestic sewage pollution

Domestic sewage refers to the waste water generated by urban organs, schools and residents in their daily lives, including toilet excrement, washing and bathing water, kitchen and other household drainage, as well as the drainage of businesses, hospitals and amusement places. The daily discharge of urban domestic sewage per capita is 150-400L, which is closely related to the living standard. Domestic sewage contains a lot of organic matter, such as cellulose, starch, sugar and fatty protein. It also often contains pathogenic bacteria, viruses and parasite eggs; Inorganic salts, such as chloride, sulfate, phosphate, bicarbonate and sodium, potassium, calcium, magnesium, etc. These domestic sewage are generally characterized by high organic matter content and easy to cause corruption. In addition, under anaerobic bacteria conditions, malodorous substances, such as hydrogen sulfide and mercaptan, are easily produced. Moreover, when these domestic sewage contains a lot of synthetic detergents, it will do great harm to human body. Domestic sewage is generally turbid, and the biochemical oxygen demand is generally 30-700 mg/L. Domestic water consumption is large and complicated, and it directly enters the water body without treatment, which seriously pollutes the water environment.

4. Water pollution caused by municipal solid waste.

Urban domestic waste mainly includes kitchen waste, waste plastics, waste paper, broken glass, metal products, etc. China has a large population and a large amount of domestic garbage. The urban population of more than 500 million is calculated at 1kg per day; More than one billion rural people produce 0.5kg daily and 65.438+0 million tons of domestic garbage every day. Due to the increasing population, domestic waste is increasing at the rate of 10% per year. The utilization rate of domestic garbage is low. A large number of acidic, alkaline and toxic wastewater containing mercury, lead and cadmium are produced in the storage or landfill project, which seeps into the surface water or groundwater, causing the water body to be black and smelly, the shallow groundwater can not be used and the water quality deteriorates. 60% of rivers in China are polluted by ammonia nitrogen, volatile phenol and permanganate, and fluoride seriously exceeds the standard, and the water body loses its self-purification function, which affects the reproduction of aquatic organisms and the utilization of water resources.