It is estimated that the world discharges more than 700 billion cubic meters of sewage every year, causing 5.5 trillion cubic meters of fresh water pollution, equivalent to more than 44% of the global river runoff. China currently discharges 34.9 billion tons of wastewater every year. It is predicted that even if it is controlled, by the year 2000, the annual discharge of industrial wastewater in China will still reach 50 billion tons, and the urban sewage will also reach 20 billion tons. At present, the Yangtze River receives as much as 654.38+03 billion tons of sewage every year, and swallows 3.5 million tons on average every day. Among them, more than 40 kinds of pollutants have been detected, including 6,543,800 tons of phenol and cyanide, 6,543,800 tons of arsenic and toxic metals such as mercury, chromium, cadmium and lead, and nearly 10,000 tons of oil. It is predicted that after 2000, the Yangtze River will contain more than 30 billion tons of sewage every year. At present, according to rough statistics, there are more than 40,000 industrial and mining enterprises, more than 65,438+600,000 urban pollution sources and more than 400 large-scale pollution sources in the Yangtze River Basin. Of the six cities in China with sewage discharge exceeding 2 million tons, four are along the Yangtze River, namely, Shanghai, Wuhan, Chongqing and Nanjing. At present, the Yellow River receives an average of 5 million tons of sewage every day. The average value of nitrogen, oxygen and mercury in Ningxia section of fertile Hetao exceeded the standard by 50% and 36% respectively, and the highest value of mercury exceeded the standard by 65438 0.6 times, which made the water pollution in China very serious.
The use of urban property (production, management, office, residence, etc.). ) is a major water pollution, and its water pollution mainly comes from industrial waste liquid pollution and domestic waste water pollution. Of course, there are other types of water pollution, such as secondary water pollution caused by sewage leakage from landfills, medical sewage pollution, water pollution caused by toxic and dangerous goods and radioactive substances infiltrating into water, and so on.
(A) industrial waste liquid pollution
Industrial waste liquid pollution has been produced since urbanization, and it is still a serious problem. There have been examples of Thames pollution in London and Minamata strange disease in Japan in history. The Japanese Nitrogen Fertilizer Company located in Minamata Bay was expanded into a synthetic acetic acid plant on 1932, and started to produce acetaldehyde and vinyl chloride on 1949, and discharged wastewater containing a large amount of methylmercury into Minamata Bay, which seriously polluted the water quality, sediments and organisms in the bay and caused Minamata disease. The number of patients reached 2227, of which 225 died.
About half of the cities in China use groundwater as water supply source. According to the investigation of 44 cities, 4 1 city is polluted by aldehydes, cyanogens and arsenic, among which 9 cities are heavily polluted and 17 cities are moderately polluted. Twenty-seven major rivers in China (including Yangtze River, Yellow River, Songhua River, Pearl River and Xiangjiang River) have been polluted to varying degrees, of which 15 is seriously polluted. For example, the phenol content of Fenhe (Taiyuan section) exceeds the national standard by 3800 times, making it a veritable "phenol river"; The content of phenol and mercury in Huaihe River (Bengbu section) exceeded the standard by 56 times and 9 times respectively. As a drinking water source in Shanghai, Huangpu River receives about 5 million tons of industrial and urban sewage every day. Every summer, the river turns black and stinks for as long as 1978 days. Urban industrial sewage is discharged directly without treatment, which directly harms surface water and groundwater. Most municipal water source wells and unit-owned water source wells do not meet the drinking water quality standards, and some wells contain phenol, chromium and amino substances, which exceed the control standards by dozens to hundreds of times. The mercury content in Songhua River water, which is 23km downstream of Jilin Chemical Industry Company, is as high as 2.3-20μ g/L, which is 1.4-5 times higher than that in the water where Minamata disease originated in Japan. In some areas of China, groundwater is overexploited blindly, and water resources are exhausted, resulting in land subsidence and forming a "funnel". As a result, there are more than 30 "funnels" in Hebei Plain, with an area of10.3 million square kilometers, and a large number of wells are forced to be scrapped, resulting in water shortage.
(2) Domestic wastewater pollution
From the perspective of the whole world, both developed and developing countries have one thing in common, that is, the main sources of water pollution have gradually changed. In the era of public hazards, toxic and harmful substances discharged by industrial and mining enterprises are the main source of serious harm to people, livestock, agriculture and fisheries; However, in the mass high consumption society, the source of water pollution has become mainly the excessive nutrients contained in domestic sewage discharged into water areas, leading to red tides, black water and other water pollution phenomena.
Red tide was discovered earlier in Tokyo Bay, Japan, and it lasted longer and longer, and it appeared earlier and earlier every year. Red tides were discovered in Tokyo Bay in 1960s, usually from the end of May to September every year. 1In April, 962, red tides suddenly appeared in two inlets around Tokyo Bay, about 50 days earlier. This is because the discharge of domestic sewage makes the water body more and more nutritious.
The direct cause of red tide is the excessive inflow of nutrients such as nitrogen and phosphorus from domestic sewage into water areas, especially closed inner bays, inland seas and lakes that are not easy to flow. These waters have poor fluidity and are easy to accumulate dirt and breed aquatic organisms such as algae. A large number of planktonic microorganisms then multiply and accumulate rapidly, making the water body dark brown, so it is called red tide.
People have noticed that the rise and fall of red tide has a certain relationship with industrial production and living consumption. After the mid-1970s, eutrophic sewage in domestic drainage was the main cause of red tide. 1973 the oil crisis in the middle east led to fuel shortage, and Tokyo reduced production by about 20%. The red tide phenomenon has not been alleviated, but has increased. Because although the discharge of industrial sewage has decreased, the dirty components such as nitrogen and phosphorus in domestic drainage have begun to increase. At 1979, 55% of nitrogen discharged into Tokyo Bay comes from domestic drainage, while at 1989, 58% of phosphorus comes from domestic drainage. The growth of this kind of public nuisance is a remarkable feature of the mass high-consumption society. Guangzhou now discharges more than 2 million tons of sewage every day, and domestic sewage is the main part. The popularization of flushing toilets with water makes toilets extinct, and other domestic sewage is directly discharged into rivers without treatment, which seriously pollutes the Pearl River waters.
In addition to industrial waste liquid and domestic sewage, there are also medical sewage and sewage pollution, poor drainage of urban roads, pit water to raise mosquitoes and flies and other pollution.
Second, the harm of property water pollution
In the process of using the property, the pollutants discharged into the water body caused by the activities of all people exceed the limit capacity of substances in the water body or the self-purification ability of water to substances, which will destroy the original use of the water body and form pollution to the water body itself, sediment pollution and aquatic organisms. This series of water pollution will inevitably bring disastrous consequences to human beings and nature. Generally speaking, the harm caused by water pollution can be divided into three aspects: damaging human health, destroying natural resources and reducing the efficiency of economic activities.
Water pollution is harmful to human health.
Water is not only an important environmental factor, but also an important part of human body. The water content of adults accounts for about 65% of their body weight, and the physiological water demand per person per day is about 2 liters to 3 liters. All physiological activities in the human body, such as body temperature regulation, nutrient transport and waste excretion, need water to complete. Therefore, water pollution will directly or indirectly damage human health.
Urban water pollution is quite common in China, and has developed to a very serious degree in recent years. Incidents and accidents of sewage endangering health are increasing year by year. For example, 1992, drinking water polluted by methanol in Dingzhou City, Hebei Province, caused dozens of people with visual impairment, and some of them were blind; In Xuzhou City 1992 and Fuzhou City 1999, Jiangsu Province, there were vicious accidents in which septic tanks communicated with reservoirs, causing pollutants such as feces to enter reservoirs and water tanks and be drunk by people, leading to acute diarrhea for most people. Drinking water sources in urban rivers and waters are seriously polluted, which makes many cities suffer from water shortage. For example, the water pollution of Huaihe River is serious, and urban residents along the Yangtze River once cooked with mineral water. Suzhou River is dark and shiny, and it is a household name. Cities such as Shanghai can no longer take water from nearby to meet the water demand of urban residents; Guangzhou is located in the center of the Pearl River Basin, with wide waters, passing through the city and dense water networks. But now, due to excessive pollution, it has entered the ranks of water-deficient cities.
In addition, in polluted water, phenols, aldehydes, petroleum and organochlorine in organic pollutants also have direct and far-reaching harm to human health. Most synthetic polymers represented by organochlorine are extremely difficult to decompose in natural environment, and the harm time is long. Like heavy metals, these substances can be integrated by aquatic organisms for millions of times and then enter the human body through the food chain, which is harmful to health. According to research, this kind of harm can continue to the second generation or even the third generation. With the widespread use of organic pesticides, organochlorine pollution has become a worldwide problem.
(b) Water pollution destroys natural resources.
The harm of water pollution is also manifested in the destruction of natural resources, especially after aquatic resources are polluted, the destruction or even destruction is extremely serious.
In the process of production and life, sewage and sewage contain a lot of aerobic pollutants (carbohydrates, fats, protein, etc. ) it is gradually decomposed into carbon dioxide and water under the action of dissolved oxygen in water, which requires a lot of oxygen. Under normal circumstances, at 20℃, the dissolved oxygen in water is only 9.17 ml/L. Due to the consumption of aerobic pollutants decomposition, the dissolved oxygen content in water drops sharply, and even an anaerobic layer is produced. This will suffocate or kill a large number of fish that depend on dissolved oxygen. At the same time, lack of oxygen will make bacteria, especially anaerobic bacteria, multiply in large quantities, promote the decomposition of organic matter and release toxic gases such as methane and hydrogen sulfide, which will further worsen the water quality and be even more unfavorable to the survival of fish. If pollutants are continuously injected, the water will be in a state of hypoxia for a long time, fish resources will be destroyed, and the water will turn black and stink, becoming toxic and harmful stagnant water.
"Eutrophication" caused by plant nutrients such as nitrogen and phosphorus in sewage can also become an important factor of hypoxia hazard. When the nutrients of plants in the water are too rich, the lower plants such as algae in the water will multiply in large numbers, occupy a lot of space, isolate the contact between air and water surface, and thus reduce the dissolved oxygen in the water. As a result of further development, cyanobacteria with colloidal membranes replaced diatoms and green algae, occupying the whole water area. Cyanophyta is not suitable for fish food, and some species are poisonous. The reproduction of cyanobacteria reduces the living space of fish, and the dead algae consumes a lot of dissolved oxygen, which will lead to the death of fish due to lack of oxygen. 1In August, 972, a "red tide" in the Seto Inland Sea in Japan caused14.28 million tail fish to die, with a loss of 7 1 100 million yen. "Red tide" is actually a phenomenon that red algae multiply in large numbers, which leads to seawater discoloration. The further development of lake eutrophication will also make the lake silted up into a swamp and eventually turn into a dry land, thus cutting off water resources.
The pollution of acid, alkali and inorganic salts in sewage also has great influence on agricultural soil. For example, long-term irrigation of farmland with acidic water with pH less than 5.5 will inhibit the growth of nitrifying bacteria in the soil, the nitrogen fertilizer will not be fully released, the fertilizer efficiency of phosphate will also be reduced, and the calcium and magnesium components in the soil will also be easily lost, which will greatly reduce crop yield and even become barren land. In addition, irrigating farmland with water with high concentration of alkali and inorganic salts will also cause soil salinization and crop yield reduction.
(C) Water pollution will reduce economic benefits
The influence of water pollution on industrial, agricultural and other production activities is mainly manifested in the low utilization efficiency and serious waste of resources and energy, and the decline or instability of the quality of the products produced, which directly leads to low output rate and output level, high product prices, loss of market competitiveness, and ultimately reduces the economic benefits and even losses of enterprises. For example, the original seven products of Dalian Cotton Mill were rated as high-quality products in all provinces of China. Now, due to water pollution, the washing process can't meet the requirements. As a result, out of 420,000 meters of colored woven fabrics, only 20,000 meters meet the high quality standards. The water quality in Bengbu and Huainan sections of Huaihe River Basin is affected by water pollution, and the products produced by coastal factories are all degraded to inferior products within half a year from19781to1979. According to the statistics of 15 factory, the loss caused by shutdown is100000 yuan. The polluted river water was used as cooling water in Jilin Chemical Fertilizer Plant, which led to the scaling and blockage of cooling equipment and pipelines, the cooling efficiency decreased by 30%, and the annual output of synthetic ammonia decreased by 1 1,000 tons. In addition, sewage from industrial areas in the suburbs of the city polluted farmland, resulting in regular compensation. For example, 198 1 This year, Shanghai compensated 932,000 yuan and Chongqing compensated 636,000 yuan. Similar situations often occur all over the country, causing very serious economic losses.
Third, prevention and control of property water pollution.
The random discharge of domestic sewage and industrial waste liquid is the main cause of property water pollution. Therefore, to prevent water pollution, we must first cut off the source, that is, control the discharge of sewage and combine prevention, treatment and management. Specifically, we should start from the following aspects:
(A) reduce sewage (wastewater) emissions
Changing the traditional industrial development model, reusing industrial water, recovering waste liquid as much as possible and minimizing the total amount of industrial water are the basic methods to reduce sewage discharge. It is also an effective measure to urge industrial and mining enterprises to reduce water consumption as much as possible to implement differential prices for excessive and high-priced water charges. For example, the water dyeing process is replaced by waterless printing and dyeing process, and the recovery equipment of blast furnace gas washing water is installed to realize multi-purpose and mutual influence, which can save a lot of water. At present, many countries are studying how to develop the treated and purified urban sewage into a new water source and reuse it in industry, agriculture, fisheries and urban residents' lives, which is also an effective way to reduce and save water.
(2) Reduce the harm degree of discharged sewage.
Minimizing the concentration of pollutants through comprehensive utilization or technical improvement can also effectively reduce pollution. For example, cyanide-free electroplating process is used to replace cyanide electroplating method, and soft detergent is used to replace hard detergent that cannot be decomposed naturally. For another example, papermaking black liquor is one of the main pollution sources, which contains a lot of organic substances such as alkali. Through comprehensive utilization, useful substances such as alkali and dimethyl sulfoxide can be recovered from it and become a production resource. For domestic drainage, the amount of pollutants should be controlled. For example, in saitama waters near Tokyo, 73% of organic pollutants are caused by domestic drainage. 1992, the county launched the first campaign to reduce pollutants in domestic drainage, and the method was very specific. For example, the kitchen sink should be equipped with garbage bags that can filter water, and the rice washing water should be kept for washing dishes to reduce its emissions. Soy sauce, wine and cooking oil that seriously affect the water quality should not enter the sewer. Wash dishes first and then wash them to reduce the use of detergents.
(c) Strengthen waste water treatment and put an end to random discharge.
In order to ensure that the water body is not polluted, proper treatment must be carried out before the wastewater is discharged into the water body, so as not to affect the sanitary state and economic value of the water body. For industrial waste liquid containing special harmful substances, special treatment or recovery facilities should be set up in the factory for treatment, and it can be discharged into public sewage channels only after reaching the specified sewage discharge standards. The discharge of domestic sewage must be treated before it can be discharged into natural water bodies.
Sewage treatment also involves a lot of sludge left after sewage treatment in sewers. With the improvement of sewage treatment level, sludge is no longer directly discharged into rivers as before, so the amount of sludge is increasing. Sludge should be buried in time, otherwise it will increase the burden and cost of a new round of sewage treatment. At present, the technology of making some building materials from sludge has been developed: burning sewage sludge and making building materials from incineration ash. The utilization rate of sludge ash in Nagoya, Japan has reached 23% in 1992, which is an environmental protection method worth learning.
(4) Strengthen the monitoring and management of water bodies and their pollution sources.
Regularly monitor the water use and drainage of the property to find out whether the water pollution of the property conforms to the relevant national regulations and standards, so as to ensure the safety and health of the water users of the property, and at the same time ensure that it will not cause influence and harm to the outside world. In this way, the prevention and control of property water pollution can be carried out with goals and directions, which is an indispensable and effective means to prevent serious water pollution.