preventive measure
1 Cause analysis of water pollution
1. 1 Water pollution caused by urbanization
In urban areas, most of the land is covered by roofs, roads and parking lots, and the ground permeability is poor. When rain falls to the ground, it is usually absorbed by the soil, some by plants, some by underground and some by surface water. Therefore, urbanization has changed the nature of the underlying surface. When it rains, rainwater meets the ground with poor permeability, forcing it to cross everywhere, and taking away a lot of urban pollutants in the process of rainwater cross-flow. Usually, these rainwater are directly discharged into local rivers through urban drainage pipes without any treatment. In this way, there will be more negative effects. First, it pollutes rivers, streams or lakes that receive rainwater. It is found that urban runoff contains high concentrations of copper, lead and zinc, which is enough to kill many kinds of fish and invertebrate aquatic animals. Rainstorm is also the main carrier of toxic metals, chlorinated organics and suspended solids. Secondly, urban runoff often comes suddenly, unlike the slow filtration of soil and plants, the power of water will scour the riverbed and destroy the aquatic environment; Thirdly, because all the storm water is introduced into the local rivers at such a high rate, the water that is not stored seeps into the streams and rivers in the dry season, which may cause the streams to dry up completely and the water surface of the rivers to drop greatly, which will also destroy the aquatic environment. Meanwhile, in some cities, rainfall may cause another headache? Mixed sewage overflows. Because the mixed sewer can be used as a drainage channel for rainwater and domestic sewage at the same time. Therefore, in the rainy season, it discharges sewage and rainwater at the same time, and sometimes the amount of water discharged to the sewage treatment plant is too much, far exceeding its treatment capacity. Excess water (mixed sewage overflow) is directly discharged into the water area without any treatment or only after primary treatment, resulting in water pollution.
1.2 water pollution caused by industrialization
There are many kinds of industrial pollutants, and each industrial sector will produce its own unique combined pollutants. Like urban sewage, industrial wastewater also contains suspended solids, various organic substances and heavy metals. If discharged directly into water without treatment, they will pollute rivers and lakes, consume oxygen in water and threaten human health. With the increase of mining and industrial activities, the production and utilization of heavy metals have greatly increased, resulting in serious heavy metal pollution in lakes and rivers. At the same time, the discharge of acid wastewater from mining industry will also produce pollution.
1.3 water pollution caused by intensive agriculture
Modern agriculture is characterized by high-tech investment, mechanical farming, chemical fertilizer and micro-irrigation, drip irrigation and sprinkler irrigation. ), field agricultural technical measures (covering orange stalks or plastic films, protecting fertilizers and crops, applying drought-resistant fertilizers and spraying water-retaining agents), selecting drought-tolerant varieties, increasing the proportion of dry farming and field water-saving management measures, and vigorously promoting comprehensive water-saving agriculture.
2 China's water environment status
The State Environmental Protection Administration (SEPA) pointed out in the Bulletin on China's Environmental Situation (1999) that in recent years, the China government has intensified the strategic adjustment of economic structure, continued to adopt a proactive fiscal policy to stimulate domestic demand, increased investment in urban infrastructure construction and environmental protection, and strengthened comprehensive environmental improvement, effectively controlling the total amount of pollution emissions and improving the environmental quality of some regions and cities. However, according to the statistical analysis of environmental monitoring results, the national environmental situation is still quite grim, the total discharge of various pollutants is very large, and the pollution level is still at a fairly high level.
At present, China's water environment is characterized by widespread organic pollution in major rivers, serious eutrophication in major lakes, widespread pollution in river sections flowing through cities and a certain degree of pollution in coastal waters. The water quality in the Yangtze River basin is good, and the main stream and main first-class tributaries still basically maintain L and surplus water quality. The water quality in the Pearl River Basin is generally good. 87% of the sections of Xijiang River are Grade I water quality, and all sections of Beijiang River are Grade I and Grade I water quality. Dongjiang 90 section is L-class water quality, and Guangzhou section of the main stream is relatively polluted.
The Yellow River basin is facing the dual pressures of water shortage and water pollution. 1999 has been cut off for 42 days, 1 14 water quality.
Among the monitoring sections, the proportion of water quality sections with Grade V and worse than Grade V is 63. 1%, and the main rivers Fenhe, Weihe, Luo Yi and Qinghe are seriously polluted. Songhua River Basin is at a moderate pollution level, with the main stream 17 water quality monitoring sections accounting for 17.6% of Class I and L water quality sections and 70.6% of Class IV water quality sections. The water quality of the main stream of Huaihe River Basin is still good, and the water quality of tributaries is mainly N to worse than V, and the Haihe River Basin is seriously polluted. 17 1 In the water quality monitoring section, the ratio of Class V to worse than Class V is 49.7 latitude. The Liaohe river basin is seriously polluted. Of the 52 water quality monitoring sections, 69.3% are inferior to Grade V (the proportion of the main stream is as high as 86.7%). The pollution in Shenyang section of Hunhe River, Tieling section of Daliao River and Anshan section of Taizi River is particularly prominent. Taihu Lake basin is in a state of moderate eutrophication, and the water quality section ratio of 10 1 water quality monitoring point is 65.4%. The Dianchi Lake Basin is seriously eutrophic. 13 of the water quality monitoring points, 63.8% are V-class inshore waters. According to the monitoring results of 368 stations, 4
Grade I and Grade IV seawater account for 15% and 28.5% respectively. The water quality in the East China Sea is 53% worse than Grade IV, and the coastal waters of Shanghai, Zhejiang, Guangdong and other provinces and cities are seriously polluted. 1999 * * China sea area record 15 red tide, Noctiluca scintillans red tide occurred in Liaodong Bay in mid-July, covering an area of 6,300 square kilometers and lasting for 9 days. According to the statistics of 1999, the national wastewater discharge is 40 1. 1 100 million tons, (including 203.8 domestic sewage. COD emission is13.889 million tons (including 6.972 million tons of domestic sewage and 69170,000 tons of industrial wastewater). The discharge of industrial wastewater and its COD showed a downward trend, while the discharge of domestic sewage and its COD showed an upward trend, and both exceeded industrial wastewater.
3 Measures to prevent water pollution
To solve the existing water pollution problem, the government and enterprises must rely on the support of science and technology, especially through scientific and technological research, on the one hand, to overcome some key and difficult problems in water treatment, on the other hand, to transform the country? Seven or five? 、? Eight-five? 、? Ninth Five-Year Plan? During this period, we will integrate and apply the mature technologies developed, explore the supporting technical and economic policies, and establish demonstration projects such as urban sewage treatment and sludge disposal, small town sewage treatment and resource utilization, industrial wastewater treatment in key industries, and non-point source pollution control in combination with the regional control project planning with outstanding water pollution problems that need to be solved urgently. This can not only obviously improve the quality of regional water environment, but also provide a scientific demonstration for water pollution control in China, which is of great strategic significance for the early solution of water pollution problems in China.
3. 1 In view of the large amount of urban sewage, it is necessary to carry out research and demonstration on high-efficiency and low-consumption treatment technology.
Urban sewage treatment is one of the key industries in the field of capital construction in China at present and in the future. By the end of 1998, China had built 187 urban sewage treatment plants, but the secondary treatment capacity was only 8.22 million m3/d. According to this calculation, the secondary treatment rate of urban sewage was only 14. 1%. At present, China has a sewage treatment plant for every 654.38+/kloc-0.00 million people, Britain and Germany have a sewage treatment plant for every 0.7-0.8 million people, and Sweden and France have a sewage treatment plant for every 500,000 people. The sewage treatment rate in developed countries is 50~70%, and in many countries it is above 85%. However, the sewage treatment rate in China is growing slowly, which is currently less than 15%. According to the national economic and social development? Ninth Five-Year Plan? According to the requirements of "Planning" and "20 10 Vision Outline", by 20 10, the urban sewage treatment rate will reach 40-50%, the investment demand of urban sewage treatment industry will be about180 billion yuan, and the annual operating cost will exceed 7 billion yuan after completion. According to the requirements of Integrated Wastewater Discharge Standard (GB897- 1996), in order to meet the wastewater discharge standard, most urban sewage treatment plants must adopt secondary biochemical treatment or advanced treatment technology. At the same time, an important problem encountered in the implementation of water pollution prevention and control planning in many areas of China is the shortage of funds for the construction and operation of sewage treatment plants, which leads to the delay in the completion of a number of planned sewage treatment plants, and the completed sewage treatment plants cannot operate normally and cannot achieve the expected environmental protection goals. It can be seen that in order to improve the sewage treatment rate in a short time, it is very important to develop feasible, efficient and low-consumption urban sewage treatment technologies, processes and equipment suitable for China's national conditions in addition to formulating reasonable and feasible industrial technical and economic policies and increasing investment in the construction of urban sewage treatment plants.
3.2 In view of the rapid development of domestic sewage in small towns, research and demonstration of low-cost treatment technology must be carried out according to local conditions.
At present, there are more than 1.9 million small towns in China. With the rapid development of township enterprises and the continuous concentration of rural population, the sewage discharge of small towns is increasing, and the amount of sewage produced is about 2000 ~ 5000 m3/d, but most of them have no effective sewage treatment facilities, resulting in very serious local water pollution and affecting the quality of regional water environment. This is very prominent in the southeast coastal areas of China, and the task of treatment is very urgent. ? Ninth Five-Year Plan? During this period, China invested tens of billions of yuan to build more than 200 urban sewage treatment plants. It is unrealistic to solve the domestic sewage problem in small towns in the same way, regardless of the construction cost or operation cost, and it is even more unbearable in underdeveloped areas. Therefore, it is of great significance to focus on solving the problems of high construction cost and high operation cost of sewage treatment facilities, develop complete sets of simple and efficient sewage treatment technologies in small towns according to local conditions, formulate reasonable and feasible industrial technical and economic policies, and demonstrate them in different types of areas.
3.3 For industrial wastewater from key industries, it is necessary to carry out key technology research and integrated application demonstration.
Due to the weak industrial base in China, the traditional extensive production mode with high consumption, low output and heavy pollution is still widely used. It is very difficult to treat refractory industrial wastewater, such as papermaking wastewater, dye wastewater, pharmaceutical wastewater, coking wastewater, etc., which is highly toxic, high in concentration and not biodegradable, and it is difficult to meet the discharge standards. Especially in the booming township enterprises, most of the production methods are relatively extensive, which leads to increasingly serious pollution. During the period of 65438-0997, the wastewater discharged by township enterprises in China was 3.9 billion tons. Due to the serious pollution and scattered pollution sources, it is difficult to implement environmental protection laws and regulations, and it is often discharged at will without treatment. The wastewater from oil production and oil refining industry also lacks effective technical means to achieve the discharge standard, which has become an environmental problem that puzzles Harada and its processing enterprises in China. Despite years of efforts and several five-year plans
Scientific and technological breakthroughs have been made in wastewater treatment in many industries in China, and the discharge rate of wastewater reaching the standard has also increased year by year. However, there are still some key industries that lack key technologies for wastewater treatment, especially in terms of systematicness and practicality, which urgently need technical progress and engineering demonstration. Therefore, focusing on the treatment of industrial wastewater in key industries and aiming at the main problems, it is of great significance to carry out research and demonstration in combination with high-concentration organic industrial wastewater, toxic and harmful industrial wastewater and oily wastewater to solve the pollution problem of industrial wastewater in China.
3.4 In view of the increasingly prominent problem of scattered non-point source pollution in rural areas, it is urgent to carry out research and regional demonstration of control technology.
Non-point source pollution caused by extensive use of pesticides and fertilizers is the main cause of water pollution in lakes and reservoirs, especially eutrophication. The monitoring and analysis of pollution sources in some polluted lakes show that non-point source pollutants have exceeded point source pollutants. Due to long-term pollution, the concentration of nutrients in the water body is unusually high, which makes the water environment very fragile. The slight change of external conditions will make the nutritional state of the water body plummet and cause frequent blooms. Eutrophication of water bodies has become a water environmental problem in many important areas of China. Controlling non-point source pollution has become an important topic of water environmental pollution. In river basin and regional water pollution control, point source pollution and non-point source pollution must be considered comprehensively. The prevention and control of non-point source pollution is not only conducive to the storage and purification of polluted runoff in the basin, but also conducive to saving the input of chemical fertilizers and pesticides in agricultural production. However, the research foundation of non-point source pollution control technology in China is still very weak. For a long time to come, China will continue to be in the process of rapid urbanization, the total urban population will increase from the current 380 million to 670 million, and the amount of urban sewage will also increase significantly. However, there is still a big gap between the secondary treatment rate of urban sewage in China and the national average treatment rate of urban sewage in 20 10. At present, the most common problem in industrial wastewater treatment is still refractory organic industrial wastewater, and there are almost no non-point source pollution control projects in major rivers and regions in China. Facing such an arduous task, apart from formulating reasonable and feasible industrial technical and economic policies and increasing investment in the construction and operation of water treatment projects, it will be an effective way to develop and integrate high-efficiency and low-consumption treatment technologies suitable for China's national conditions.
4. Conclusion
The rapid development of China's economy is achieved under the condition of relatively backward economy and technology. With a large population base and few per capita resources, it will be a long-term strategic task to prevent and control environmental pollution and ecological destruction. In particular, the water pollution problem is difficult to solve in a short time and needs a hard treatment process. Therefore, we must be in line with international standards, learn from successful experience, strengthen international exchanges and cooperation, and at the same time, combine the development reality of China, constantly strengthen policy innovation, system innovation and technological innovation, and gradually embark on a road of water pollution prevention with China characteristics. People should also start from themselves, start from small things, strictly demand their own behavior, protect the environment, and contribute to the harmony between mankind and nature.