Pollution control analysis of Qingshan Reservoir

Qingshan Reservoir is located in the lower reaches of nantiao River in Lin'an, Hangzhou. It was built in 1964 with a total storage capacity of 2.15 * 108 m3, with a catchment area of 603km2 and a water area of 20.2km2. The dam height is 24.1m. Nantiao River in the upper reaches originates from the East Tianmu Mountain, runs through Lin'an City from north to Southeast, and successively receives six main tributaries, Nanxi, Panxi, Maxi, mianxi, Hengxi and Lingxi, with an average flow of 4.82m3/s. The number of hydrological monitoring for many years It is shown that the annual runoff in the upper reaches of nantiaoxi is 188 million cubic meters, which accounts for 72.5% of the annual runoff from April to September. From November to January of the next year, the runoff accounts for 7.3% of the annual runoff. The 20% assurance rate is 260 million cubic meters in wet year, and the 95% assurance rate is 103 million cubic meters in dry year.

The terrain of the basin is mostly low mountains and hills, sloping from the west to the southeast. The content of soil nitrogen and phosphorus is medium and low, showing weak acidity. The climate is humid, with four distinct seasons. The annual average temperature is 15.8oc, and the annual average rainfall is 1432.6mm. The basin where the reservoir is located is an area with relatively concentrated population and developed tertiary industries such as politics, economy, culture, commerce and tourism.

Because nantiaoxi is in flood season and has large water flow, a large amount of sediment in the upstream is washed to Qingshan Reservoir by flood. The buffering effect of the reservoir makes the sediment deposit at the bottom, so Qingshan Reservoir is mainly composed of sediment. According to the investigation, the bottom material at the entrance of Mian and Lingxi is still black and muddy. The Zoobenthos Community of the reservoir is mainly composed of oligochaetes and chironomid larvae. There are few molluscs, less aquatic higher plants, but more plankton.

2.1 urban domestic sewage pollution

In recent years, with the rapid development of economy, the built-up area of Lin'an City is expanding day by day, and the urban population is growing rapidly. The area of the built-up area of Jin town is about 80000 square meters, and the population is about 80000. With the increase of urban population, the discharge of urban sewage is also increased artificially. According to the survey, the daily discharge of domestic sewage in Lin'an City is about 40000 tons. So far, the urban domestic sewage has not been treated and discharged into Qingshan Reservoir (the first phase of sewage treatment project is under commissioning) If we take CODcr 0.06 kg / person / day, tn0.01 kg / person / day and tp0.002 kg / person / day as the calculation, the daily production of urban pollutants in Lin'an City is CODcr 4.8 tons, tn0.8 tons and tp0.16 tons. According to the urban planning, it is estimated that the population of Lin'an will reach 150000 by 2010, and the daily discharge of domestic sewage pollution in Lin'an will be 9 tons of CODCr, 1.5 tons of TN and 0.3 tons of tp0.3 tons in 2010. In this way, the pollution load of Qingshan Reservoir will be further increased, and the water quality of Qingshan Reservoir will be further deteriorated.

2.2 industrial wastewater pollution

Industrial waste water is the main cause of Qingshan Reservoir pollution. In recent years, the industrial economy of Lin'an City has been growing steadily, and the industrial pollution sources have remained relatively stable. Through "one control and two standard work". The discharge of industrial pollutants has been reduced. According to the Emission Declaration statistics, in 2000, the daily discharge of industrial pollution sources into Jinxi was about 31000 tons, and the daily discharge of CODCr was about 5500 kg. The industrial wastewater discharged into Lingxi is about 6600 tons per day and the CODcr is about 850kg per day. The industrial pollution source discharged into nantiaoxi, the upper reaches of Qingshan Reservoir, discharges about 7000 tons of industrial wastewater and 600 kg of CODCr per day. The total amount of industrial wastewater discharged directly or indirectly into the pollution source of Qingshan is about 44600 tons per day, and the amount of codcr6950 kg per day. Therefore, in terms of the impact of industrial pollution on Qingshan Reservoir, the industrial pollution sources along Jinxi River should be the key prevention and control objects.

2.3 agricultural non-point source pollution

Agriculture is the foundation of national economy. In recent years, Lin'an City has witnessed steady development of agriculture, especially the development of breeding industry of native products. The development of agriculture has brought about a large increase in the use of chemical fertilizer. According to the investigation and statistics of agricultural non-point sources, the total amount of chemical fertilizer applied in paddy field, dry land and garden land along nantiaoxi River in the upper reaches of Qingshan Reservoir is 7153.4 tons / year. Among them, nitrogen fertilizer (n) is 1672.7 tons / year, phosphorus fertilizer (P2O5) is 318.25 tons / year; the total amount of fertilizer application in paddy field, dry land and garden land along Lingxi is 3089 tons / year, including nitrogen fertilizer (n) of 468.3 tons / year, phosphorus fertilizer (P2O5) of 68.25 tons / year; the total amount of fertilizer application in paddy field and dry land along Jinxi is 2046.8 tons / year, including nitrogen fertilizer (n) of 339.3 tons / year, phosphorus The fertilizer (calculated by P2O5) is 91.5 tons / year. The use and loss of chemical fertilizer elements, especially the entry of N and P elements into the water body, promote the eutrophication of Qingshan Reservoir.

2.4 pollution of catering and entertainment industry

The catering and entertainment industry along the Bank of Qingshan Reservoir is also an important reason for the deterioration of Qingshan Reservoir. Today, there are nearly ten hotels along the Bank of Qingshan Reservoir, which discharge about 700 tons of waste water and 70 kg of CODCr per day. Second, recreational boats are just the main cause of oil pollution. The environmental awareness of tourists is shallow, which is also one aspect of the damage to the reservoir water quality. The input of solid waste destroys the structure of water body and increases the load of self purification.