Water pollution and its harm

Water pollution refers to the phenomenon that the pollutants discharged into the water body exceed the self-purification ability of the water body, which leads to the deterioration of water quality. The causes of water pollution are natural and man-made. Generally speaking, water pollution refers to man-made pollution. Man-made pollution is the water pollution caused by human life and production, including a large number of untreated domestic sewage, industrial wastewater and farmland drainage discharged into the water.

All kinds of substances that worsen water quality, biomass and sediments can be called water pollutants or water pollutants. According to the different hazards of environmental pollution, water pollutants can be divided into the following categories: solid pollutants, biological pollutants, aerobic organic pollutants, nutrient-rich pollutants, sensory pollutants, acid-base pollutants, toxic pollutants, oil pollutants, thermal pollution and so on.

1. Solid pollutants

There are three forms of solid matter in water: dissolved, colloidal and suspended.

2. Biological pollutants

Biological pollution refers to pathogenic microorganisms and other harmful organisms in wastewater. Mainly including viruses, germs, parasitic eggs and other pathogens. In addition, if iron bacteria, sulfur bacteria, algae, aquatic plants and shellfish grow in wastewater, it will block pipelines, corrode metals and worsen water quality, and it is also a biological pollutant.

Biological pollutants mainly come from urban domestic sewage, hospital wastewater, garbage and surface runoff. The water pollution of pathogenic microorganisms has the longest history, and it is still an important type that harms human health and life.

3. Organic pollutants to be oxidized

Substances in wastewater that can consume dissolved oxygen in water through biochemical and chemical actions are collectively called aerobic pollutants. The vast majority of aerobic pollutants are organic matter. The same characteristic of organic matter is that these substances directly enter the water body and are decomposed into simple inorganic substances-carbon dioxide and water through the biochemical action of microorganisms. In the process of decomposition, dissolved oxygen in water needs to be consumed. A large amount of organic matter will lead to almost complete consumption of oxygen, and aerobic fish and zooplankton will die in this environment.

Chemical oxygen demand (COD) and biological oxygen demand (BOD) are commonly used to describe the determination of oxygen-consuming organic compounds in water.

4. Nutritional pollutants

Eutrophication pollutants refer to substances that can cause eutrophication of water bodies, mainly nitrogen, phosphorus and other elements, and others include potassium and sulfur. In addition, biodegradable organic matter, vitamins and thermal pollution can also trigger or promote the process of nutrition. The nutrients in the water mainly come from chemical fertilizers, which enter the water body with agricultural drainage. Secondly, they come from human, livestock and poultry feces and phosphorus-containing detergents. In addition, the wastewater discharged from food factories, printing and dyeing factories, tanneries and explosives factories contains a lot of nutrients such as nitrogen and phosphorus.

Excessive nutrients entering natural water will worsen water quality, affect fishery development and endanger human health.

5. Sensory pollutants

Substances in wastewater that can cause abnormal color, turbidity, foam, odor and other phenomena, although not harmful, can cause sensory discomfort, which is called sensory pollutants.

6. Acid, alkali and salt pollutants

Acid-base pollutants are mainly caused by acid-base and acid rain discharged from industrial wastewater. Acid-base pollutants change the pH of water, destroy the natural buffering effect, eliminate or inhibit the growth of bacteria and microorganisms, hinder the self-purification of water, worsen water quality, and acidify or alkalize soil.

Acid and alkali enter the same water body at the same time From the pH value, the pollution of acid and alkali is self-purified by neutralization, but it will produce various salts and become new pollutants in water. The increase of inorganic salts can increase the osmotic pressure of water and affect the growth of freshwater organisms and plants. In salinized areas, the salt in surface water and groundwater endangers soil quality, and the hardness of water is increased by acid, alkali and salt pollution.

7. Toxic pollutants

Substances that can cause biotoxic reactions in wastewater are called toxic pollutants, which are called poisons for short. There are more than 12000 kinds of toxic chemicals used in industry, and the number is increasing at the rate of 500 kinds every year. A large number of toxic substances discharged into the water body not only endanger the survival of aquatic organisms such as fish, but also can be gradually transferred and concentrated in the food chain, and finally enter the human body, endangering people's health.

Toxic pollutants in wastewater can be divided into three categories: inorganic poisons, organic poisons and radioactive substances.

Inorganic poisons, including metals and nonmetals. Metal poisons are mainly mercury, cadmium, nickel, zinc, copper, manganese, cobalt, titanium and vanadium. The light metal is beryllium. Non-metallic poisons include arsenic, selenium, cyanide, fluoride, sulfide and nitrite. Heavy metals can bioaccumulate in the body, and sometimes they can be biotransformed into more toxic substances (such as inorganic mercury being converted into alkyl mercury).

Organic poisons, most of which are synthetic, are difficult to biodegrade and have great toxicity. Organic poisons of great significance in environmental pollution include pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, aromatic amines, heterocyclic compounds, phenols, nitriles and so on. Many organic poisons have "three effects" (teratogenesis, mutation and carcinogenesis) and accumulation (enrichment in the food chain, endangering human health).

Radioactive substances, radioactive substances in wastewater mainly come from the production and use of radioactive metals such as uranium and radium, such as nuclear testing, nuclear fuel reprocessing and raw material smelting. Its concentration is generally low, which will mainly cause chronic radiation and late effects, such as inducing cancer, causing harm to pregnant women and babies, and causing genetic damage.

8. Oil pollutants

Petroleum pollutants include mineral oil and animal and vegetable oils. They are insoluble in water and often exist in the form of coarse dispersed floating oil and fine dispersed emulsified oil. The oil floating on the water surface forms a thin film, which affects the dissolution of oxygen in the atmosphere, thus affecting the survival of fish and the self-purification of water bodies, and also interfering with the normal operation of some water treatment facilities. Oil pollutants can also adhere to the surface of soil particles and animals and plants, affecting the absorption of nutrients and the excretion of waste. Oil pollution is mainly caused by industrial emissions, offshore oil production, cleaning of oil carriers and tanker accidents. 20 10 on may 5th, crude oil leaked in the gulf of Mexico, which seriously affected the ecological environment (fig. 6- 14, fig. 6- 15).

Figure 6- 14 seabirds struggling in the seawater polluted by crude oil in the Gulf of Mexico

Figure 6- 15 Crude Oil Contaminated Area in the Gulf of Mexico

9. Thermal pollution

The harm caused by excessive temperature of wastewater is called thermal pollution.

(B) the hazards of water pollution

The hazards of water pollution mainly include the following points.

1. Harm to human health

Water pollution directly affects the quality of drinking water sources. When the drinking water source is polluted by synthetic organic matter, it will lead to ascites, diarrhea, hepatitis, gastric cancer, liver cancer and other diseases. Contact with unclean water can also lead to skin diseases, trachoma, schistosomiasis, hookworm and other diseases. Some toxic and harmful substances in wastewater, even if the quantity is small and even difficult to detect, can still cause fatal harm to human body due to the enrichment of animals and plants and the accumulation of human body itself.

2. Reduce the yield and quality of crops.

The water in rivers and lakes is often the source of farmland irrigation. Once these water bodies are polluted, toxic and harmful substances in the water will pollute farmland soil, be absorbed by crops and remain in crops. On the one hand, it causes crops to wither and die, and the yield is reduced; On the other hand, the quality of crops will also decline to varying degrees. For example, if pollutants exceed the standard, the contents of nutrients such as protein, amino acids and vitamins will be reduced, which will make vegetables smell bad.

3. Affect fishery production

Fishery production is closely related to water quality. Accidents that cause large-scale fish deaths in freshwater fishing grounds occur from time to time. In some heavily polluted river sections, fish and shrimp have disappeared. Water pollution can also mutate fish and aquatic organisms, and toxic substances accumulate in fish, which greatly reduces the edible value.

4. Restrict the development of industry

Many industries (such as food, textile, papermaking and electroplating) need water, and the deterioration of water quality will directly affect the quality of products. If the cooling water with poor water quality will cause blockage, corrosion and scaling of the water circulation system, the water with high hardness will affect the life and safety of the boiler.

5. Accelerate the degradation and destruction of the ecological environment

Water pollution not only harms aquatic organisms in water, but also affects the ecological environment around water. After pollution, the sense of water body becomes worse, giving off peculiar smell, and pollutants in water have toxic effects on surrounding organisms, causing biological death and degradation and destroying the ecological environment.

6. Causing economic losses

Water pollution causes the environment to lose some or all of its original functions, resulting in environmental degradation and devaluation, which is harmful to human survival and economic development. Monetizing these hazards is the economic loss caused by water pollution. If it is harmful to human health, it will reduce the labor force and reduce labor productivity. If diseases occur frequently, more medical expenses will be paid, and the reduction of fish production or the deterioration of fish quality will directly cause economic losses. The cost of pollution control and ecological environment restoration will increase with the aggravation of pollution.

(3) Water quality standards

At present, China has promulgated water quality standards such as water environment quality standards and discharge standards.

Water environmental quality standards: surface water environmental quality standard (GB3838—2002), groundwater quality standard (GB/T 14848-93), seawater quality standard (GB 3097- 1997), sanitary standard for drinking water (GB 5749) and water quality standard for farmland irrigation (GB 5749).

The Environmental Quality Standard for Surface Water (GB3838—2002) classifies surface water into five categories according to its environmental functions and protection objectives:

Class I: mainly applicable to source water and national nature reserves;

Class II: It is mainly applicable to the first-class protected areas such as centralized drinking water surface water sources, rare aquatic habitats, fish and shrimp spawning grounds, etc.

Class III: mainly suitable for the secondary protection zone of centralized drinking water surface water source, fish and shrimp wintering ground and swimming area;

Class Ⅳ: It is mainly suitable for general industrial water areas and recreational water areas where human body is not in direct contact;

Class ⅴ: Mainly applicable to agricultural water use areas and waters with general landscape requirements.

Wastewater discharge standards: comprehensive wastewater discharge standard (GB 8978- 1996), hospital water pollutant discharge standard (BGJ 48-83) and some industrial water pollutant discharge standards, such as paper industry water pollutant discharge standard (GB 3544-83) and sugarcane sugar industry water pollutant discharge standard (GB 3544-83).