The world's annual discharge of sewage is estimated to have been more than 700 billion cubic meters, resulting in freshwater pollution amounted to 5,500 billion cubic meters, which is equivalent to more than 44% of the global river runoff. China currently discharges 34.9 billion tons of wastewater annually. It is predicted that, even if controlled, by the year 2000 the annual discharge of industrial wastewater in the country will still reach 50 billion tons, while urban sewage will also reach 20 billion tons. The Yangtze River currently receives up to 13 billion tons of sewage annually, swallowing an average of 3.5 million tons per day. As many as 40 types of pollutants have been monitored, including 18 million tons of phenol and cyanide, 16.3 million tons of arsenic and toxic metals such as mercury, chromium, cadmium and lead, and nearly 10,000 tons of petroleum. It has been predicted that after 2000, the Yangtze River will accommodate more than 30 billion tons of sewage annually. At present, rough statistics show that there are more than 40,000 industrial and mining enterprises in the Yangtze River Basin, more than 16,000 urban pollution sources, and more than 400 large pollution sources. Four of the six cities in the country that discharge more than 2 million tons of sewage are along the Yangtze River, namely, the big industrial cities of Shanghai, Wuhan, Chongqing and Nanjing. The Yellow River currently receives an average of 5 million tons of sewage per day. The average value of nitrogen and oxygen and the average value of mercury in the Ningxia section of the rich river-loop exceeded the standard by 50 percent and 36 percent, respectively, and the highest value of mercury exceeded the standard by 1.6 times, and the pollution of China's water quality has reached a very serious point.
The use of urban property (production, business, office, residential, etc.) is a major player in water pollution, its water pollution mainly from industrial waste liquid pollution and domestic wastewater pollution. Of course, there are other types of water pollution, such as landfill sewage leakage generated by the secondary water pollution, medical sewage pollution, toxic and hazardous materials and radioactive substances into the water caused by water pollution, and so on.
(I) industrial waste pollution
Industrial waste pollution is since urbanization has produced, and is still facing serious problems. Historically, there have been examples of pollution of the Thames River in London and the strange disease in Minamata City, Japan. The Japan Nitrogen Fertilizer Company, located in Minamata Bay, expanded into a synthetic acetic acid plant in 1932 and began producing acetaldehyde and vinyl chloride in 1949, discharging wastewater containing a large amount of methylmercury from its production into Minamata Bay, which seriously contaminated the water quality, sediments, and living organisms in the bay with mercury, causing Minamata disease to occur. The disease affected 2,227 people, of whom 225 died.
About half of the cities in China use groundwater as a source of water supply. According to a survey of 44 cities, groundwater in 41 cities is contaminated by aldehydes, cyanide, arsenic, etc., of which 9 cities are heavily contaminated and 17 cities are moderately contaminated. The 27 major rivers in the country (including Yangtze, Yellow, Songhua, Pearl and Xiangjiang) are now polluted to different degrees, of which 15 are seriously polluted. Such as the Fen River (Taiyuan) phenol content exceeds the national standard of 3,800 times, becoming a real "phenol river"; Huaihe River (Bengbu) phenol content and mercury content exceeded the standard of 56 times and 9 times; as a source of drinking water in Shanghai, the Huangpu River, every day, to accept about 5 million tons of industrial and municipal sewage, the river water in the summer dark and stinky, in 1978, the black odor Every summer, the river water becomes black and stinks, and in 1978, the black odor time was as long as 106 days. Municipal industrial sewage is discharged directly without treatment, which directly jeopardizes surface water and groundwater. Most of the municipal water wells and unit water wells do not meet the drinking water quality standards, and some of them contain phenol, chromium, amine and other substances that exceed the control standards by tens to hundreds of times. Songhua River from the Jilin Chemical Industry Company downstream of 23 kilometers of the river section of the amount of mercury in the water per liter up to 2.3 micrograms to 20 micrograms, than the sensational world of Japan's Minamata disease in the first place of mercury in the water is also 1.4 times higher than 5 times. Some areas of China blindly over-exploited groundwater, water resources depletion, causing ground subsidence, the formation of "funnel". Hebei Plain, thus forming the "funnel" has more than 30, an area of 13,000 square kilometers, a large number of wells were forced to scrap, resulting in water stress.
(B) domestic wastewater pollution
From a worldwide perspective, whether developed or developing countries have a **** the same place, that is, the main source of water pollution has gradually changed. Pollution prevalent in the era, industrial and mining enterprises in the discharge of toxic and hazardous substances is the main source of human and animal, agriculture and fisheries serious victims; and into the mass of high consumption society, the source of water pollution has become the main source of sewage contained in excessive nutrients discharged into the waters, resulting in red tides, the water quality of the black and other water pollution phenomena.
Earlier red tide was found in Tokyo Bay, Japan, the duration is getting longer and longer, and year by year in advance of the occurrence of the 1960s Tokyo Bay on the discovery of the red tide, generally the end of May to September each year. 1962 April, Tokyo Bay along the two bays of the water suddenly flooded the red tide, in advance of the 50 days or so. This was caused by domestic sewage discharges that made the waters increasingly nutrient-rich.
The direct cause of the red tide is the excessive flow of nutrient-rich salts such as nitrogen and phosphorus from domestic sewage into the waters, especially closed inlets, inlets and lakes that are not easy to flow, which have poor mobility and are prone to the accumulation of pollutants and the growth of algae and other aquatic organisms. A large number of planktonic microorganisms then rapidly multiply and accumulate, so that the color of the water is a reddish tea color, and thus known as red tide.
It has been noted that the growth of red tide is related to industrial production and consumption, and since the mid-1970s, nutrient-rich wastewater from domestic sewage has been the main cause of red tide, and when the Middle East oil crisis in 1973 led to a fuel crunch and a cut in production in the Tokyo area of about 20%, the phenomenon of red tide increased rather than eased. In 1979, 55% of the nitrogen discharged into Tokyo Bay came from domestic sewage, and in 1989, 58% of the phosphorus was discharged from domestic sewage. This increase in domestic pollution is a distinctive feature of a society of high mass consumption. Guangzhou now discharges more than 2 million tons of sewage per day, with domestic sewage being the major part. The promotion of flush toilets has made the toilet extinct, together with other domestic sewage are too late to be processed before being discharged directly into the river, seriously polluting the waters of the Pearl River.
Property water pollution in addition to industrial waste liquids, domestic sewage, there are such as medical sewage and dirt pollution, poor drainage of urban pavements, potholes, stagnant water to raise mosquitoes and flies and other pollution.
Two, property water pollution hazards
Property in the use of the process, people's activities caused by all the pollutants discharged into the water over the substance in the water body in the limit of the capacity or the self-purification of water on the substance, will destroy the original use of the water body, the formation of the pollution of the water body itself, the substrate contamination and aquatic life pollution. This type of series of pollution of water bodies is bound to bring disastrous consequences to human beings and the natural world. The harm caused by water pollution, in general, can be divided into damage to human health, destruction of natural resources and reduce the benefits of economic activities in three areas.
(a) water pollution is detrimental to human health
Water is not only an important environmental factor, but also an important part of the human body. Adult body water content of about 65% of body weight, each person's daily physiological water needs of about 2 liters to 3 liters. All physiological activities in the human body, such as temperature regulation, nutrient transport, waste excretion, etc. need water to complete. Therefore, water pollution will directly or indirectly damage human health.
China's urban water pollution has been quite common, in recent years the development of a very serious point, sewage health hazards and accidents are rising year by year. For example, in 1992, Dingzhou City, Hebei Province, because of drinking water contaminated by methanol, resulting in dozens of people with visual impairment, some of them blind; Xuzhou City, Jiangsu Province, in 1992 and in January 1999, Fuzhou City, septic tanks and cisterns connected to fecal water and other pollutants into the cisterns and water tanks, and after being consumed by the majority of acute diarrhea of the malignant accidents. Drinking water sources in urban rivers and waters are seriously polluted, causing water shortages in many cities. Such as the Huaihe River in the flow of water pollution is too heavy, city residents along the river once with mineral water to cook; Suzhou River ink black shiny is a household name; Shanghai and other cities have been unable to draw water from the near for urban residents need water; Guangzhou City in the center of the Pearl River basin in the waters of the broad, the Pearl River through the city, surrounded by a dense network of water, but now due to pollution is too much, has been across the ranks of the city into the water quality of the shortage of water.
In addition, in the polluted water, organic pollutants in the phenols, aldehydes, petroleum and organochlorine also have a direct and far-reaching harm to human health. Most of the synthetic polymer substances represented by organochlorine are extremely difficult to be decomposed in the natural environment and are harmful for a long time. These substances, like heavy metals, can be enriched millions of times by aquatic organisms and then enter the human body through the food chain, jeopardizing health. According to research, this harm can continue into the second and even third generation. With the widespread use of organic pesticides, organochlorine pollution has become a worldwide problem.
(B) water pollution damage to natural resources
The harm of water pollution is also prominent in the destruction of natural resources, especially aquatic resources are polluted, damaged or even destructive situation is extremely serious.
People in the production and living process, the discharge of a large number of oxygen-demanding pollutants (carbohydrates, fats, proteins, etc.) of sewage and dirt into the water body, the role of dissolved oxygen in the water, and gradually decomposed into carbon dioxide and water, etc., the process requires the consumption of a large amount of oxygen. However, under normal conditions, 20 ℃, the water contains only 9.17 ml / liter of dissolved oxygen, due to the consumption of oxygen-demanding pollutants decomposition, so that the content of dissolved oxygen in the water drops sharply, and even produce an oxygen-free layer. This will make the fish that rely on dissolved oxygen to survive suffocate or die in large numbers. At the same time, the lack of oxygen will also make the water bacteria, especially anaerobic bacteria multiply, and promote the decomposition of organic matter to release methane, hydrogen sulfide and other toxic gases, so that the water quality further deterioration will be even more detrimental to the survival of fish. If the pollutants are continuously injected, the water is in a long-term state of anoxia, fish resources are destroyed, the water body will also become black and stink, become toxic, harmful stagnant water.
Nitrogen, phosphorus and other plant nutrients in the sewage caused by "eutrophication", can also become an important factor in the harm of hypoxia. The water is too rich in phytonutrients, algae and other plants in the water will be reproduced in large quantities, occupy a large amount of space, and isolate the air and water contact, so that the dissolved oxygen in the water to reduce. The result of further development is that orchid algae with gelatinous membranes replace diatoms and green algae and occupy the entire water. Orchid algae are unsuitable as fish food and some species are toxic. The proliferation of cyanobacteria reduces the living space of fish, and the dead algae consume a lot of dissolved oxygen, which leads to the death of fish due to lack of oxygen. 14.28 million fish died in the Seto Inland Sea of Japan in August 1972 due to a "red tide", causing a loss of 7.1 billion yen. "Red tide" is actually a phenomenon in which seawater changes color due to red algae blooms. The further development of eutrophication in lakes will also cause them to silt up into swamps and eventually evolve into dry land and cut off water resources.
Acid, alkali and inorganic salt pollution in sewage also has a great impact on agricultural soil. For example, to the farmland long-term irrigation pH value of less than 5.5 acidic water, the growth of nitrifying bacteria in the soil will be inhibited, nitrogen fertilizer can not be fully released, phosphate fertilizer efficiency will be reduced, the soil calcium, magnesium components are easy to lose, it will make crop yields fell dramatically, and even become barren. In addition, the use of alkali and inorganic salt concentration of water irrigation farmland, will also cause soil salinization and crop yield reduction.
(C) water pollution will reduce economic efficiency
The impact of water pollution on industry, agriculture and other production activities is mainly manifested in the inefficient use of resources, energy and serious waste, the quality of products produced by the decline or instability, etc., which directly leads to the low output rate and output level, product prices, loss of market competitiveness, and ultimately reduce the economic efficiency of enterprises, and even losses For example, the original Dalian Cotton Weaving Factory has the following production line. For example, Dalian Cotton Weaving Factory original 7 kinds of products were rated as high quality products in all provinces, now because of the pollution of water quality, washing process can not meet the requirements, the result of 420,000 meters of colorful woven fabrics only 20,000 meters to meet the high quality standards. Bengbu and Huainan sections of the Huaihe River Basin, due to water pollution affecting the quality of water supply, in November 1978 to May 1979 within six months, so that all the products produced by the coastal factories downgraded to second-rate products. According to the statistics of 15 factories, the loss caused by the consequent shutdown amounted to 10 million yuan. The Jilin fertilizer factory used polluted river water for cooling water, which resulted in accelerated scaling and clogging of cooling equipment and pipes, leading to a 30% reduction in cooling efficiency and a reduction in the annual output of synthetic ammonia by more than 10,000 tons. In addition, sewage from industrial areas in the outskirts of cities polluted farmland, resulting in regular compensation. For example, in 1981, Shanghai paid out 932,000 yuan and Chongqing paid out 636,000 yuan. Similar situations occur frequently in the country, resulting in serious economic losses.
Three, the prevention and control of property water pollution
The casual discharge of domestic sewage and industrial waste liquids and so on is the main cause of property water pollution. Therefore, the prevention of water pollution should first start from the source, that is, to control the discharge of sewage, the "prevention", "treatment", "management" combination of the three. Specifically, it should start from the following aspects:
(a) Reduce the discharge of sewage (waste) water
Change the traditional mode of industrial development, so that industrial water reuse and try to recycle waste liquids, minimize the total amount of industrial water, which is the basic method to reduce the amount of sewage discharge. Through the implementation of the differential price of water over the standard high-priced charges, prompting industrial and mining enterprises to minimize the amount of water consumption, is also an effective measure. For example, the use of waterless printing and dyeing process instead of water dyeing process, blast furnace gas washing water recycling equipment, in the premise of mutual non-influence to realize a water multi-purpose, etc., can be a large amount of water savings. Now many countries are studying the treatment of purified urban sewage development for new water sources, will be reused in agriculture, fisheries and urban residents living in the method, is also an effective way to reduce and save water.
(ii) reduce the harmful degree of discharged water
Through the comprehensive utilization or technological improvements to minimize the concentration of pollutants, can also effectively reduce pollution. For example, the use of cyanide-free plating process instead of the cyanide plating method, the use of soft detergents instead of hard detergents that can not be naturally decomposed. Another example is that black liquor of papermaking is one of the major sources of pollution, containing a large amount of alkali and other organic substances, which can be turned into a production resource through comprehensive utilization and recovery of useful substances such as alkali and dimethyl sulfoxide from it. For domestic drainage, the amount of pollutants should be controlled. For example, Japan's Saitama County waters near Tokyo, 73% of the organic pollutants are caused by domestic drainage, the county in 1992, the first to carry out the campaign to reduce the pollutants of domestic drainage, the method ordered very specific, such as kitchen sinks to be equipped with water filtering garbage bags, panning the water to stay to wash the dishes to reduce the discharge of its serious impact on the quality of the sauce soup sauce, wine and cooking oil shall not enter the sewer, washing dishes should be wiped first wash after washing, to reduce the use of detergent, water, and water, and to reduce the use of detergent. Reduce the use of detergents, water to try to save and reuse, etc., which is an effective way to reduce water pollution.
(C) strengthen the wastewater treatment link to eliminate arbitrary discharge
In order to ensure that the water body is not polluted, must be properly treated before the wastewater discharged into the water body, so as not to affect the sanitary state of the water body and economic value. Industrial waste liquid containing special hazardous substances, should be set up in the factory special treatment or recycling facilities for treatment, to meet the required sewage discharge standards before discharging into the public **** sewage waterways. The discharge of domestic sewage should also be treated before being allowed to discharge into natural water bodies.
Sewage treatment also involves a large amount of sludge left after sewage treatment. With the improvement of the level of sewage treatment, sludge is not directly discharged into the river as before, so the amount of sludge is on the increase. Sludge should be landfilled in a timely manner, otherwise it will add burden and cost to the new round of sewage treatment. Technology has been developed to utilize sludge to make some building materials: the sludge from sewers is incinerated and the ash from the incineration is used to make building materials. Nagoya, Japan, in 1992, the utilization rate of sludge ash has reached 23%, which is a worthwhile environmental protection method.
(D) strengthen the monitoring and management of water bodies and their sources of pollution
Regularly monitor the property water use and drainage, to understand the property water pollution, etc. and whether it is in line with the relevant national regulations and standards, to ensure that the property users of the water safety and health, at the same time, to ensure that it does not cause any impact on the outside world and harm. This can make the property water pollution prevention and control work has a goal and direction, is to prevent the seriousness of water pollution indispensable and effective means.