I. Water pollution and its classification
About 30% of drinking water sources in China have reached or basically reached the drinking water standard, and 77.8% of cities with groundwater as drinking water sources have been polluted to varying degrees.
When people drink polluted drinking water, it will not only affect human health, but also be threatened by water-borne diseases. Here is a simple classification of water pollution.
Classification of water pollution
Pollutant category
chemistry
Oil, dyes, synthetic detergents, halogenated hydrocarbons, phenols, hydroxy acids and sugars are sexually polluted.
Inorganic acid, alkali, heavy metal salt, nitrate, phosphate, cyanide, sulfide, radioactive substance.
thing
reason
nature
dirty
Dye floating foam, scum, sawdust and leaves.
Suspended silt, sand, fine metal particles, volcanic ash, rubber particles, paper scraps,
Solid pollutants, bacterial corpses
Thermal pollution and warm drainage
biology
Sexually polluted pathogenic algae bacteria, protozoa, fungi, algae and viruses.
Excessive reproduction, decay and oxygen consumption caused by eutrophication
With the development of economy, the improvement of people's living standards, the formation and expansion of big cities and township enterprises, the discharge of domestic sewage and industrial wastewater is increasing day by day, and the sewage treatment methods often can't keep up with the development of the situation, especially the industrial three wastes discharged by some township enterprises at will, which makes the water pollution more and more serious.
Two. The main source of water pollution
1. Industrial wastewater
In industrial production, heat exchange, product transportation, product cleaning, mineral processing, slag removal, production reaction and other processes will produce a lot of wastewater. The main enterprises that produce industrial wastewater include primary metal processing, food processing, textile, paper making, mining, refining and chemical industries. According to the investigation of 1990, there are 38 state-owned enterprises in China, and there are more than 100,000 township enterprises/kloc-0. The latter are poor equipment, backward technology, large water consumption and large wastewater discharge. According to the statistics of the State Environmental Protection Bureau, from 65438 to 0992, the total industrial wastewater discharge in China was 36.65 billion tons. At present, there are more than 65,438+industrial and mining enterprises in the Yangtze River basin in China, and the whole basin receives more than 2 million tons of harmful and toxic substances, 5,000 tons of heavy metals such as mercury, chromium and cadmium, 30,000 tons of phenol and cyanide and 35,000 tons of oil every year. It is reported that the water systems that are more polluted than the Yangtze River include Songhua River, Huaihe River, Haihe River and Liaohe River. If the current pollution trend is allowed to develop and effective measures are not taken, it is estimated that by the end of last century, the total amount of wastewater discharge will increase to 410.29 billion tons, and 70% of the fresh water resources in China will be seriously polluted and cannot be directly used.
2. Domestic sewage
Domestic sewage refers to sewage from families, institutions, commercial and urban public facilities and urban runoff. Fresh urban sewage gradually decays and deteriorates, which leads to the decrease of dissolved oxygen content, anaerobic degradation reaction, hydrogen sulfide, mercaptan, indole and fecal odor, which makes the water smelly. The composition of domestic sewage is 99% water, the solid impurities are less than 65438 0%, and most of them are non-toxic. Among them, inorganic salts include cyanide, sulfate, phosphate, ammonium salt, nitrite, nitrate and some bicarbonate. Organic substances include cellulose, starch, sugar, fat, protein and urea, as well as various detergents and trace metals such as zinc, copper, chromium, manganese, nickel and lead. Domestic sewage also contains a large number of miscellaneous bacteria, mainly coliforms. In addition, the content of nitrogen and phosphorus in domestic sewage is high, which mainly comes from commercial sewage, urban surface runoff, feces, detergents and so on.
3. Hospital sewage
The sewage discharged from general hospitals, infectious disease hospitals and tuberculosis hospitals contains a large number of pathogens, such as typhoid fever, dysentery, tuberculosis, pathogenic protozoa, enterovirus, adenovirus, hepatitis virus, schistosomiasis eggs, hookworms, ascaris eggs and so on. These pathogens can often survive in the external environment for a long time. Therefore, after hospital sewage pollutes water or soil, it can spread diseases through drinking water or food for a long time. In addition, shellfish in water have the ability to concentrate bacteria and viruses, so shellfish in raw water are very dangerous after water pollution (such as the outbreak of hepatitis A in Shanghai).
4. Runoff and Infiltration of Farmland Water
In the vast rural areas of our country, it is customary to use untreated human and animal feces and urine to irrigate vegetable fields and farmland. In the past decades, the use of fertilizers and pesticides has increased rapidly. After fertilization or pesticide application, the residual fertilizers and pesticides can enter the surface water and groundwater with the runoff of farmland through the erosion of rainwater or irrigation water and the infiltration of soil. Farmland runoff contains a large number of pathogens, suspended solids, fertilizers, pesticides and decomposition products. There are many kinds of pesticides with different properties, so their toxicity is different. Some pesticides are non-toxic or basically non-toxic, some can cause acute and chronic poisoning, some may cause cancer, mutation and teratogenesis, and some have adverse effects on reproductive and immune functions.
5. Stacking, burying and dumping wastes
Some wastes temporarily stacked in the open air will be brought into the water body due to rain or wind, some wastes will be dumped into the water body artificially, and some wastes that are difficult to treat will be buried deep underground. However, if the underground disposal project is improperly set up or buried without any treatment, it will affect the geology and environment around the disposal area, and the disposed pollutants will enter the water body, causing water pollution. There has been a serious "love canal incident" in the United States that caused water pollution by solid waste. Love Canal is located near Niagara Falls, USA. In the early 1940s, Hook Chemical Company dumped about 20,000 tons of waste. Later, the garbage dump was abandoned and people lived here one after another. Toxic substances in garbage enter the drinking water system from groundwater through inverted siphon, which increases the incidence of various local diseases, especially cancer, and some babies are deformed at birth. Later, these buried wastes finally emerged from the ground due to rain erosion, and people knew the truth of the matter. A similar incident happened in Jinzhou, China. Chromium slag was piled up in Jinzhou Ferroalloy Factory in 1950s. A few years later, it was found that more than 30 square kilometers of water was polluted by hexavalent chromium. The groundwater in the central area contains as much as 55 mg of hexavalent chromium per liter, which is more than 65,438+0,000 times higher than the allowable concentration of drinking water, resulting in 65,438+0,800 wells in seven natural areas being undrinkable.
1. Sensory pollution of water body
* color change. Natural water is colorless and transparent. Water pollution will change the color of water, thus affecting the senses. For example, the pollution of printing and dyeing wastewater often turns water red, and the pollution of oil refining wastewater turns water black and brown, and so on. The change of water color not only affects the senses and destroys the scenery, but also is difficult to deal with.
* Turbidity change. Water contains suspended matter and colloid of sediment, organic matter and inorganic matter, which leads to turbidity, thus reducing the transparency of water and affecting the senses and even life of aquatic organisms.
* Bubbles. Many pollutants, such as detergents, will foam when discharged into water. The foam floating on the water surface not only affects the perception, but also harbors bacteria in its pores, causing domestic water pollution.
* Smell. Odor in water is a common pollution phenomenon. The odor of water body mostly belongs to organic matter that decays and stinks under anaerobic condition, which belongs to comprehensive odor and has obvious sewer odor. The harm of stench is that people hold their breath and feel sick, aquatic products are inedible, and water bodies lose their tourism function.
2. Organic pollution of water body
Mainly refers to the pollution caused by wastewater containing a lot of organic matter discharged from urban sewage, food industry and paper industry. These pollutants need to consume a lot of dissolved oxygen in the process of biological oxidation and decomposition in water. Once the oxygen supply in water is insufficient, it will stop oxidation, resulting in anaerobic fermentation of organic matter, giving off stench, polluting the environment and poisoning aquatic organisms.
3. Inorganic pollution of water body
Refers to the pollution of water by acid, alkali and inorganic salts. The first is to change the pH value of water, destroy its natural buffering effect, inhibit the growth of microorganisms and hinder the self-purification of water. At the same time, it will increase the hardness of inorganic salts and water in water, which will bring adverse effects on industrial and domestic water.
4. Water pollution by toxic substances
After all kinds of toxic substances enter the water body, at high concentration, they will kill the creatures in the water; At low concentration, it can be enriched in organisms and concentrated step by step through the food chain, eventually affecting the human body.
5. Eutrophication pollution of water body
When wastewater containing plant nutrients enters the water, it will cause eutrophication, make algae multiply in large numbers, consume a lot of dissolved oxygen in the water, and lead to fish suffocation and death.
6, water pollution
Oil exploitation, tanker transportation and wastewater discharge from oil refining industry in coastal and estuarine areas have caused oil pollution in water bodies. When oil forms an oil film on the water surface, it will affect oxygen entering the water body and cause harm to living things. In addition, oil pollution also destroys the landscape of beach resorts and scenic spots and the survival of birds.
7. Water thermal pollution
The cooling water of thermal power plant is the main source of thermal pollution. This kind of wastewater discharged directly into the natural water body will cause the water temperature to rise, reduce the dissolved oxygen in the water and increase the toxicity of some poisons in the water. The increase of water temperature has the greatest influence on fish, which can cause the change and death of fish population.
8. Water pollution by pathogenic microorganisms
Domestic sewage, hospital sewage, slaughter meat processing and other sewage contain all kinds of viruses, bacteria, parasites and other pathogenic microorganisms, which will spread various diseases when they flow into the water.
9. Radioactive pollution of water bodies
Refers to the pollution caused by radioactive substances entering the water body. Radioactive substances mainly come from nuclear reaction waste. Radioactive pollution will lead to biological distortion, destroy the genetic structure of organisms and cause cancer. Nuclear matter has a long decay period and cannot be handled.