1. What is water pollution?
Water pollution refers to the phenomenon that the physical, chemical, biological or radioactive characteristics of natural water are changed due to the intervention of some substances, thus affecting the effective utilization of water, endangering human health or destroying the ecological environment, resulting in the deterioration of water quality. Water pollution generally means that the amount of pollutants in water exceeds the self-purification ability of water body; The amount of pollutants has reached the level of destroying the original use of water; The content of pollutants has exceeded the background value of the substance in water, thus affecting the use of water.
2. Types of water pollution
According to the existing forms of water, it can be divided into surface water pollution and groundwater pollution; According to the nature of pollutants, there can be physical water pollution and chemical water pollution; According to the classification of water areas, there are river pollution, lake pollution, reservoir pollution and marine pollution. According to pollutants, there can be metal pollution, acid-base pollution, organic pollution, thermal pollution and so on. Just a few categories are discussed here.
2. 1 metal pollution
Metal pollution refers to heavy metals that pollute water bodies, mainly including mercury, cadmium, lead and metalloid arsenic, as well as general heavy metals with certain toxicity. This paper briefly introduces the hazards of the following important toxic heavy metals.
2. 1. 1 Mercury pollution and its harm
Mercury pollution mainly comes from wastewater discharged from chemical plants, chlor-alkali plants, pesticide plant, smelters and mercury detectors. Mercury in the form of metallic mercury is not toxic, and most mercury can pass through the digestive tract without being absorbed. Mercury and its compounds are harmful to the leaves, buds and petals of plants, but the serious decline of reproductive function of birds will lead to the death of birds, damage the function of enzymes in human body and the function of central nervous system, cause teratogenesis and genetic harm, and make people suffer from Minamata disease, hepatitis and hematuria. Mercury and its compounds can also cause fetal congenital mercury poisoning through placenta, and can also poison infants through breast milk, making them stunted, mentally retarded, deformed and even paralyzed.
2. 1.2 Harm of lead and its compounds
Lead will affect photosynthesis and transpiration of plants and reduce crop yield. Lead can also damage the liver and heart of human beings and animals, make the development slow, make the head muscles, joints, spleen, bone marrow and nervous system sick, and even lead to the death of animals and people.
2. 1.3 Hazards of arsenic and its compounds
Arsenic can change the color of plants, wither leaves and reduce crop yield. It can also destroy the enzyme function of animals and people, cause pathological changes of nervous system and capillary generator, and make animals and people suffer from cancer.
2.2 Acid-base pollution
Acid-base pollution refers to a water pollution phenomenon with abnormal acid-base concentration in water. The PH value of natural water is 6.5 ~ 8.5. When the PH value is less than 6.5 or greater than 8.5, it means that the water body is polluted by acid and alkali. The acidic substances in the water mainly come from acid-containing sewage such as self-made acid plants, chemical plants, viscose fiber plants and pickling workshops, as well as mine drainage and acid rain. The alkaline substances in the water mainly come from the wastewater of alkaline substances such as pulp mills, paper mills, alkali plants, printing plants, tanneries and oil refineries. When the PH value of water is less than 6.5 or greater than 8.5, the growth of microorganisms in water will be resisted. Acid-base pollution will increase the salt content of water, which will have adverse effects on industry, agriculture, fishery and domestic water. Serious acid-base pollution will also corrode ships, bridges and other water buildings.
2.3 Organic pollution
There are many kinds of organic matter in the water.
2.3. 1 ODS
Oxygen-consuming organic matter will lead to a significant decline in dissolved oxygen content in water. Most organic matter in water can be decomposed and utilized by microorganisms, and this kind of organic matter needs to consume dissolved oxygen in water during decomposition, so it is called oxygen-consuming pollutants. The sharp drop of dissolved oxygen is a remarkable feature of water polluted by organic matter. A large number of aerobic organisms enter the water body and are decomposed by aerobic microorganisms, which greatly reduces the dissolved oxygen in the water body and even causes hypoxia, which is harmful to aquatic organisms and sometimes leads to a large number of fish deaths. When the dissolved oxygen is exhausted, the organic matter turns into anaerobic decomposition process, which produces reducing substances such as methane, hydrogen sulfide, ammonia and odor, which makes the water quality worse.
2.3.2 Refractory organic matter
Refractory organic matter refers to organic matter that is difficult to degrade under natural environmental conditions. Most of them are synthetic chemicals, which are characterized by long-term stable storage and biochemical accumulation in the food chain. Some compounds have carcinogenic, teratogenic and mutagenic effects even at very low levels, which pose a great threat to human health.
3. Countermeasures for water pollution prevention and control
3. 1 Improving the utilization rate of water resources can not only increase water resources, but also reduce the discharge of polluted water and water pollution. The water utilization rate can be improved from the following aspects.
3. 1. 1 Improve the utilization rate of agricultural irrigation water.
The utilization efficiency of agricultural irrigation water determines the utilization of water resources in the whole country. Efficiency In recent years, China's agricultural water-saving work has made great progress in two aspects: one is the increase in investment, and the other is the substantial increase in the research and popularization of new water-saving irrigation equipment and technology.
According to estimates, if water-saving agriculture is developed scientifically, by 2030, the water utilization coefficient of China's reform can reach 0.6 ~ 0.7, the water productivity can reach 1.5 kg/m3, and the utilization rate of agricultural irrigation water can be increased by 0.3. Based on the current 400 billion cubic meters, it can save water by 654.38+02 billion cubic meters and increase grain production by 654.38+02 billion tons.
3. 1.2 Improve the utilization rate of industrial water.
The utilization rate of industrial water in China is not high, and the serious waste of water resources is also widespread. Coastal cities in China have used seawater to cool down for more than 60 years, but at present, the utilization amount is not large, wasting a lot of water resources. Generally speaking, the higher the utilization rate of industrial water, the greater the investment in water saving, which almost increases exponentially. The most important economic and financial constraints to improve industrial utilization rate have no potential to be tapped. In China, the reuse rate of urban industrial water (excluding electricity) in 20 10 is set at 75%, which is one of the long-term control targets of industrial water utilization rate in China.
3.2 Develop sewage treatment technology according to local conditions
In view of the shortage of water resources in China, the uneven distribution of water resources in time and space, and the differences in economic development in different places, different countermeasures should be taken in the choice of sewage treatment technology.
In southern China, the natural purification capacity of rivers and seas should be scientifically utilized to develop urban sewage discharge projects based on the characteristics of relatively rich water environmental capacity and primary treatment. We can take advantage of the crisscross of small rivers and lakes in the south, rationally plan the scientific layout, and appropriately develop some oxidation ponds, oxidation ditches, oxidation lakes and nitrogen and phosphorus removal technologies.
In the northern and central regions, water shortage is a prominent contradiction. Focus on the reuse of sewage resources and develop the secondary utilization, comprehensive utilization and reuse of sewage resources. In order to realize sewage reuse, we should adjust the setting of urban drainage pipe network and sewage treatment plant accordingly, and develop secondary biological treatment technology.
In the western plateau and arid and semi-arid areas, it is mainly to formulate measures to improve the ecology and develop some sewage reuse technologies and land treatment technologies.
In view of the shortage of water resources and serious water pollution in the world, let's work together to make this earth more beautiful! !