Talk about the prevention and control of water pollution in Taihu Lake from Wuli Lake
Kou Zhuxi
Abstract Wuli Lake is a bay in the north of Taihu Lake. Since the 1990s, , due to the large amount of domestic and industrial sewage flowing into the lake, the lake water was seriously polluted. In recent years, Wuxi City has invested a lot of manpower and material resources to control the water pollution of Wuli Lake, and adopted comprehensive measures such as ecological dredging and ecological restoration to control pollution, and achieved obvious results. The pollution practice of Wuli Lake has certain reference significance for water pollution control in Taihu Lake. Based on the pollution control practice of Wuli Lake, some suggestions are put forward for the treatment of Taihu Lake.
Keywords Wuli Lake, Great Lakes Ecological Dredging, Water Pollution
1. Wuli Lake water pollution prevention and control has achieved initial results
Wuli Lake is also called Li Lake. It is a bay in the northern part of Taihu Lake. Before the 1970s, the water in Wuli Lake was crystal clear, and aquatic plants drifted with the current. Due to land reclamation from the lake, the area of ??Wuli Lake has been shrinking since the 1970s, and it has returned to the current 5.8km2 after several twists and turns. Since the 1990s, due to a large amount of domestic and industrial sewage flowing into the lake, there is no one to collect mud and silt from the lake. Due to secondary pollution, the water quality of Wuli Lake is getting worse and worse, the water ecology has been severely damaged, aquatic plants have died, the water body has become seriously eutrophic, and algae blooms occur in summer. According to the evaluation of the "Surface Water Environmental Quality Standard GB3838-2002", many water quality indicators in Wuli Lake at the beginning of the 21st century were worse than Class V.
In order to control the pollution of Wuli Lake, Wuxi City has invested a lot of money and implemented comprehensive measures for many times. In 2002, 50 million yuan was invested in ecological dredging (also known as environmental dredging) using advanced environmentally friendly dredging equipment. 2.48 million m3 were dredged, which reduced secondary pollution of the bottom sludge and increased the water depth by 40-50cm; in 2003, it was five years. The water pollution control of Lihu Lake has achieved remarkable results in a year. First, 250 million yuan was invested to return fish to the lake. The 219hm2 fish pond around the lake was completely cleared of silt at the bottom and returned to Wuli Lake. To this end, 48 industrial enterprises were relocated at the same time, greatly reducing the number of fish ponds. It has eliminated fish pond pollution and industrial pollution, expanded the area of ??Wuli Lake by 2.19km2, and invested 45 million yuan to implement the "863" plan to control water pollution in Taihu Lake - Wuli Lake ecological restoration and ecological dredging research, and has restored 100hm2 of aquatic life. The plant area not only uses aquatic plants to absorb nitrogen and remove phosphorus to purify the water body, but also adds to the ornamental value of the lake area. On this basis, another 120 million yuan was invested to build the Meiliang Lake Pumping Station with a pumping capacity of 50m3/s, and implement water transfer and exchange for Wuli Lake, Meiliang Lake and Wuxi City. Millions of yuan have also been invested to build a fountain with a spray height of over 100 meters at the fish return site in the north of West Wuli Lake, called the "Light of Lihu Lake", which is both a landscape and can increase dissolved oxygen. Based on the phased results of the "zero" point operation in 2000 (the closure of domestic sewage outfalls into the lake from hotels, restaurants, guest houses, nursing homes, etc.), the sewage interception project around Wuli Lake was implemented and the fish nets and fish traps in the lake were dismantled. , stocking 2 million silver carp and bighead carp fry.
After treatment, the water quality of Wuli Lake has improved significantly. The monthly test results from April to December 2003 showed that the permanganate index of Wuli Lake was 7.6 mg/L (Class IV). Compared with 2002, it decreased by 10.6, total phosphorus was 0.127mg/L (Class IV), which decreased by 36.2, total nitrogen was 6.41mg/L (slightly decreased), and the transparency increased from the original 20-30cm to 40-60cm. The water quality improvement effect is better in the center of the lake than at the mouth of the river, and in West Wuli Lake it is better than in East Wuli Lake. Among them, the best water quality improvement effect is in the large area in the northern part of West Wuli Lake where fish are returned to the lake. The reason is that this area has been thoroughly dredged, the river entrance to the lake has been blocked, aquatic plants have been planted, and high fountains have been built. According to the monthly test results from January to April 2004, the average permanganate index in the area is 5.69 mg/L (Class III), total phosphorus is 0.03 mg/L (Class III), total nitrogen is basically the same, and the transparency is sometimes Can reach more than lm. The water in Wuli Lake has returned to the clarity it had in the 1950s and 1960s, and land prices around Wuli Lake began to appreciate as a result.
Although Wuli Lake water pollution control has achieved relatively obvious results, the water quality has not been fundamentally improved, and total nitrogen remains high. It is still far from the Class IV water target of the water functional zone in 2010. The task of controlling water pollution in Wuli Lake is still very arduous. According to its natural and geographical characteristics, comprehensive water pollution prevention and control measures should be further improved and implemented.
2. Water pollution in Taihu Lake
1. Causes of water pollution in Taihu Lake
First, the amount of pollutants in the human lake exceeds its self-purification capacity. The main sources of pollutants are secondary pollution from external sources such as industry, life, planting, breeding, water and soil erosion, shipping and tourism, rainfall and dust fallout, and internal sources such as silt accumulated at the bottom of the lake for a long time.
Secondly, the prevention and control of water pollution in Taihu Lake is not progressing rapidly. Mainly manifested in insufficient investment, serious shortage of sewage treatment capacity, insufficient control of external and internal sources, slow ecological restoration progress, lagging planning and implementation, unreasonable development and utilization of water resources, and lax law enforcement.
2. Key areas of water pollution in Taihu Lake
The first is the lake bay. The eastern half of Taihu Lake is lightly polluted, while the western half is more polluted. Especially the three bays of Wuli Lake, Meiliang Lake, and Zhushan Lake are the most polluted lakes in Taihu Lake, with the fastest pollution development and the greatest harm. The current annual average water quality of the Bay is worse than Class V. The main pollution indicators are total nitrogen and total phosphorus. In 1990, 1994, 1995, and 1997, major algae outbreaks or serious "lake flooding" occurred, and the lake water stinked, seriously affecting People's lives and economic construction have been affected by algae outbreaks almost every year since then.
The second is the mouth of the river entering the lake. Mainly the lake entrances of Yixing and Huzhou in the upper reaches of Taihu Lake and the lake entrances of Zhihu Port, Wujin Port and Liangxi River of Meiliang Lake. The rivers entering the lake bring a large amount of domestic, industrial and agricultural pollutants into the lake.
3. The focus of water pollution prevention and control in Taihu Lake is Wuli Lake, Meiliang Lake, Zhushan Lake and the rivers entering the lake
Wuli Lake, Meiliang Lake and Zhushan Lake If the most polluted lake bay is cured, the water pollution of the entire Taihu Lake will also be cured. Controlling the pollution on both sides of the main rivers entering the lake and significantly reducing the pollutants brought into the lake are also top priorities in preventing and controlling water pollution.
3. Several suggestions for the prevention and control of water pollution in Taihu Lake
1. A unified pollution prevention and control plan for each region should be formulated
Each region should be organized in the Taihu Basin Management Agency Under the leadership of the State Council, corresponding water pollution prevention and control plans shall be formulated in a unified manner according to its specific natural, social and economic conditions. The basic measures for the prevention and control of water pollution in each region are to control external sources, properly remove internal sources, and take corresponding key measures according to the specific situation. For example: Wuli Lake should be completely closed, the water level should be raised, a reservoir should be built, and ecological dredging and ecological restoration should be implemented. ; Meiliang Lake is a large pocket-shaped lake, and the focus should be on controlling the external sources of the human lake channel and both sides, blocking pollution, dredging, water diversion and ecological restoration; Zhushan Lake is a small pocket-shaped lake and should be based on Source control, ecological dredging and ecological restoration are the main tasks; Gong Lake is an open bay, and water diversion, pollution prevention and ecological restoration should be the main focus; East Tai Lake is a downstream bay, and ecological dredging and ecological management should be the main focus. Mainly; the west bank and south bank of the upper reaches of Taihu Lake mainly focus on source control.
2. Properly determine the total amount of pollutant control targets
It is necessary to correct the view of some people that as long as industrial sewage reaches the standard discharge and domestic sewage is treated centrally, other things such as controlling external sources , dredging, water diversion, building gates to block pollution, ecological restoration and other engineering and technical measures and safeguard measures are also completely necessary and crucial. For example, the current total COD (Chemical Oxygen Demand) discharge of urban pollutants in Wuxi is 4.5 times greater than the allowable pollutant capacity in 2010, and NH3-N is 3.25 times greater. At present, 96% of major industrial enterprises have reached discharge standards, but the river water has not been discharged for a long time. It is still in a black and smelly state, so the sewage discharge standards should be raised and the total amount of pollutants should be appropriately determined to control the total amount of pollutants.
The Taihu Lake Basin is economically and socially developed, and the total amount of pollutant discharge is several times greater than the allowable amount of pollutants. Each region needs to appropriately determine its total amount of pollutant control targets. Otherwise, even if the discharge reaches the standard partially, it will overwhelm Taihu Lake after the confluence.
To this end, the relevant departments must, on the one hand, work out a more realistic allowable amount of pollutants, but on the other hand, they should not place too much emphasis on the indicator of the allowable amount of pollutants. What is important is to focus on effectively reducing various types of pollution loads and improving the environment. On capacity.
3. Effectively control industrial pollution
Clean production should be implemented throughout the entire process, and processes, technologies, equipment, and raw materials that produce no or less pollutants should be used for decades or more. It will take a longer time for industrial enterprises to achieve "zero" emission of pollutants. At present, it is only the minimum and most basic requirement for industrial enterprises to meet emission standards. Due to the developed economy of the Taihu Lake Basin, there are many factories, especially in cities and towns. Even if all large, medium and small industrial enterprises meet emission standards, their pollutant emissions are still very large. Measures such as takeover, relocation, restructuring and closure should be adopted at present. Among them, takeover is to connect all industrial sewage (excluding circulating water discharged by power plants or thermal power plants and other wastewater that does not increase pollution, the same below) into the sewage collection pipe network and enter the sewage plant for treatment. Some that cannot be directly entered the sewage plant should be pre-treated After passing the qualification, they can enter the sewage treatment plant; relocation means moving heavy polluting enterprises into corresponding industrial parks, and classifying sewage treatment according to different types.
4. Build sufficient high-standard sewage treatment systems
Construct sufficient sewage treatment plants and their supporting pipe networks to ensure that all industrial and domestic sewage enters the sewage plant for treatment. Urban sewage plants mainly deal with domestic sewage and also deal with industrial sewage. Township sewage plants should deal with both industrial and domestic sewage. For example, the current treatment capacity of Wuxi City's sewage treatment plant has exceeded 500,000 t/d, accounting for about 60% of domestic sewage discharge, and is at the forefront of Jiangsu Province. However, due to insufficient pipe network facilities, the actual treatment rate is still only 30-40%. Industrial The rate of sewage entering the sewage treatment plant is even lower. Therefore, all regions in the Taihu Lake Basin must increase investment and build sufficient sewage treatment systems as a hard task to control industrial pollution. The top priority is to explore a market-oriented operation path.
With the increase in sewage treatment capacity and the control of domestic and industrial pollution, the water treated by sewage treatment plants will be the largest pollution load in the Taihu Lake Basin. Therefore, the discharge standards of sewage plants should be improved to minimize Pollution load from wastewater treatment plants. For example, Wuxi urban sewage treatment plant, if it still adopts the secondary emission standard ("Urban Sewage Treatment Plant Pollutant Discharge Standard GBl8918-2002", the same below) in 2010, only the COD (Chemical Oxygen Demand) of pollutants discharged by the sewage plant will This item will exceed the allowable pollution holding capacity of the urban COD. Therefore, in economically and socially developed cities in the south of the Yangtze River, the pollutant discharge standards of sewage plants should be raised to Class A standards, which can reduce COD emissions by half compared to Class II standards.
5. Close urban sewage outlets to control agricultural and rural pollution
There are tens of thousands of domestic and industrial sewage outlets in the Taihu Lake Basin, which is very difficult to manage. In order to ensure that industrial and domestic sewage enters the sewage plant for centralized treatment and facilitates supervision and management, all urban industrial and domestic sewage outfalls must be closed. The closure of rural sewage outfalls should be determined based on the local allowable sewage holding capacity.
Agricultural and rural pollution must be strictly controlled. Agricultural pollution includes planting and breeding (poultry and fisheries), and rural pollution is domestic pollution. Main control measures: First, vigorously promote rural urbanization, build residential areas, centralized living, and centralized treatment of domestic sewage; second, comprehensively build agricultural and rural pollution control areas. An agricultural and rural pollution control area is a major agricultural area that adopts a unified and complete set of pollution control measures to control pollution from planting and breeding in the area as well as domestic pollution from scattered farmers. Attention should be paid to the control of other non-point source pollution, which refers to non-point sources other than agriculture. Mainly, pollutants generated by accumulations on the ground, roads, squares, roofs and vehicles enter water bodies with rainwater, and rainfall and dust fall. At the beginning of every heavy rain, the rainwater discharged from the urban rainwater pipes is black, which shows the huge pollution load. Control measures are: planting more trees and grasses, increasing greening and vegetation coverage, and reducing surface runoff; comprehensively building interception-type rainwater and sewage diversion systems in cities and towns to reduce non-point source pollution from entering water bodies.
6. Continuous ecological dredging
Ecological dredging is carried out to improve water quality and aquatic ecological environment. The purpose is to reduce secondary pollution, which is different from improving navigation. and dredging to relieve waterlogging and flood conditions. The implementation of ecological dredging in Wuli Lake has achieved good results. The first dredging of rivers in Wuxi urban areas has been completed, and the first dredging of rural rivers will also be completed. After ecological dredging, the water ecological environment of Wuxi City has been significantly improved. The improvement effects are in order: Wuli Lake, Yixing Rural Area, Xichengpian Rural Area, General Town, and Wuxi Urban Area. This shows that the effect of ecological dredging on improving the water environment is related to the pollution of the water body, the pollution of the substrate, the rate at which pollutants are released from the substrate, the flow rate of the water body, etc. It is also related to the method of desilting and the mechanical equipment used. It is related to the quality of dredging.
What should be emphasized here is that ecological dredging must control the depth of ecological dredging. In the Taihu Plain river network area and lakes, areas with serious pollution and siltation, and silt accumulated in the past 30-40 years, all need to be dredged. For cleaning, sludge that has been formed for a long time, has low pollutant content, and produces less secondary pollution can be cleaned.
Ecological dredging must use appropriate mechanical equipment and methods, and the cycle and time of ecological dredging must be mastered. Areas in Taihu Lake and other lakes need to be dredged once every 15-20 years, and river networks need to be dredged every 5- Once every 10 years. Ecological dredging will achieve better results after basically controlling external sources. At the same time, ecological dredging should be coordinated with ecological restoration projects. In areas where submerged and emergent plants are planned to be planted, consideration should be given to appropriately reducing the depth of dredging or eliminating dredging.
7. Building gates to block pollution is a simple and feasible pollution control method unique to the middle and lower reaches of Taihu Lake
Before external pollution is completely controlled, building gates to block pollution can effectively control some of the pollution. Pollutants are removed from the lake to protect key waters. For example, the Liangxi River, Zhihu Port, and Wujin Port of Meiliang Lake have all built gates to block pollution, reducing the amount of pollutants in the lake by 40-60%; the 14 rivers of Rengong Lake have all built gates and begun to block pollution. It is necessary to strengthen pollution control management and solve the problems of pollution control and coordination with flood discharge and waterlogging on both sides of the 14 rivers in Zhihu Port, Wujin Port and Rengong Lake.
8. Properly raise the water level of Taihu Lake
The domestic, industrial and ecological water consumption of cities around Taihu Lake continues to increase with social and economic development, so it is necessary to raise the water level and increase the water storage capacity; To control water pollution in Taihu Lake itself, it is also necessary to raise the water level and increase the environmental capacity. The Taihu Lake embankment and its related culverts, gates, and pumping stations have been completed. Taihu Lake has initially formed a lake that can be closed and can artificially adjust the water volume. Taihu Lake's flood control standards have been greatly improved. Taihu Lake's water level and water storage capacity have been appropriately raised. possible. The increase in the water level of Taihu Lake should be considered to be 3.20m (Wusong benchmark) in dry periods and 3.40m in normal times. If it is lower than the above standard, water should be transferred and replenished in time; it is recommended that the flood control warning level of Taihu Lake be appropriately increased to 3.60-3.80m according to the actual situation.
9. Reasonable water transfer is an effective measure to improve the water quality and increase the water volume of rivers and lakes in the Taihu Lake Basin
The Wangyu River has built a clear water corridor. In recent years, water from the Yangtze River has been transferred to Taihu Lake every year, improving the The water quality on both sides of the Taiwan Strait and Taihu Lake has achieved good results, and the diversion of the Yangtze River to Taihu Lake has been affirmed by the central leadership. Water diversion of Wangyu River should continue without hampering flood control. When the Wangyu River Project was originally designed, it was impossible to foresee such a high speed of economic and social development in the Taihu Lake Basin and a huge increase in ecological water consumption. Therefore, the existing Wangyu River can no longer meet the needs of water diversion and water supply in the basin, and other water supplies should be added. The line diverts water from the Yangtze River. For example, if the Xingou River is built to divert water from Zhihu Port to Meiliang Lake clear water channel, the flow rate is 100-200m3/s or larger, which can supplement the water resources of Taihu Lake and effectively improve the water quality of Meiliang Lake and Xichengpian river network, and also Wangyu River can be expanded to increase water diversion capacity.
10. Accelerate ecological restoration
Taihu Lake had a good ecosystem in the 1950s and 1960s. At the end of the 20th century, the ecosystem in the eastern half of Taihu Lake was acceptable, while the western half was severely damaged. Severe damage, the variety and quantity of aquatic life have been greatly reduced. The current successful experience of ecological restoration in Wuli Lake and the experience of three previous ecological restorations (at the water intake of Zhongqiao Water Plant, the water intake of Meiyuan Water Plant and next to the Lakeside Hotel) show that ecological restoration has a significant effect on improving water quality, but it must Choose biological species carefully and pay attention to long-term management.
Multiple wetland reserves should be established. Water intakes of Taihu Lake with a daily water intake of 50,000 tons and above should establish water source wetland protection zones, and estuary wetland protection zones should be established at the mouths of larger rivers to function as oxidation ponds and mainly plant emergent plants. The area of ??wetland protection areas should be 2-5km2; lake wetland protection areas should be established in lakes between river networks. Near towns, landscape lakes can also be built; in some places, fish ponds or low-lying areas can be used to excavate and build new wetland protection areas. , while meeting the needs of ecology, flood storage, and flood detention; ecological restoration projects should pay attention to establishing a long-term mechanism, otherwise they will not be sustainable.
11. Strengthen scientific research and water resources monitoring to achieve full sharing of data
Comprehensive water pollution prevention and control model tests in Taihu Lake and various regions in the basin, demonstration tests in agricultural and rural pollution control areas, and control Information such as research on the effective pathways of total nitrogen and total phosphorus, research on the mechanism of algae outbreaks, research on the machinery and methods of algae removal and algae absorption, and research on the comprehensive utilization of silt and algae should be shared throughout the basin.
It is necessary to strengthen water resources monitoring, including river water volume and water quality monitoring and sewage water volume and water quality monitoring. Each water functional area must have one or several monitoring points, and every sewage outlet must be monitored. Increase monitoring frequency and transition to automated monitoring. The implementation of universal sharing of monitoring data is conducive to the determination of pollution control plans, the measurement of pollution control effects and the supervision of pollution control.
Taihu Lake benefits the entire basin, and the entire basin must make every effort to protect Taihu Lake. The basin is a whole, and agencies at all provincial, municipal, and county levels within the basin should, under the unified arrangement of the central government, accelerate the pace of water pollution prevention and control, so that the Taihu Lake water will become clear as soon as possible, and create a good water environment for sustainable economic and social development. ■