1. eutrophic lake sediment pollution causes and research overview
Eutrophication is an important indicator of serious pollution of water bodies. Serious eutrophication of lakes leads to the collapse of lake aquatic ecosystems. A large number of fish, shrimp and higher plants die. Instead, they adapt to various micro-organisms that pollute, Seriously affected the economic development of our country. Sources of lake pollution can be divided into: point source, surface source and endogenous three. Pollutants enter the body of water through atmospheric deposition, waste water discharge, rainfall leaching and scouring, and finally sediment to the bottom of the lake and are gradually enriched to contaminate the sediment. Accompanied by the rapid economic development, this phenomenon is more and more serious. Including organic debris, toxic and refractory substances, heavy metals and other sediments deposited in lake sediments, resulting in increased sediment pollution. When the point source pollution and the non-point source pollution are large, the sediment can enrich these pollutants. When the point source pollution and the non-point source pollution are controlled, these pollutants deposited in the sediment are widely used in physics and chemistry And biological under the action of complex changes in the sediment, and then release water pollutants, aquatic ecosystems constitute a threat or even damage, is the cause of sediment pollution. And the more eutrophic lakes, the more serious the phenomenon is after the external pollution is brought under control. Data show that after the Dianchi Lake in Yunnan external pollution control, the release of phosphorus in the sediment can also maintain the current level of Dianchi Lake water for 63 years; Changchun South Lake study also illustrates the same problem.
Currently at home and abroad on lake pollution treatment technology can be divided into two kinds of ectopic and in situ processing techniques. After years of practical research, both technologies have been well developed and have been applied in many lakes and achieved some success. For example, the Trummen lake in Sweden, after removing 1m thick sediment, the water depth increased by 1.1 ~ 1.7m. The phosphorus content of the lake decreased by 90% and the average biomass decreased from 75mg / L to 10mg / L. After the Dudai grassland project of Dianchi Lake in China was 4 million m3, after the implementation of the project, TN39600t, TP7900t, Respectively, 5.9 times and 7.0 times of annual pollution control of nitrogen and phosphorus pollutants, dredging area is no longer black and smelly water, water quality improved significantly, the water transparency from the original less than 0.37m to 0.8m; In addition, Anhui Chaohu and Hangzhou West Lake, through the dredging of sediment to remove a large amount of nitrogen, phosphorus and other internal pollution load, making the water quality in the dredged after a period of time has been greatly improved. In situ treatment technology, Japan's Lake Biwa, Lillesjon Lake, Sweden, using in situ chemical treatment technology and found that sediment release rate of phosphorus decreased significantly; Washington Dnny Harbor, Japan Kihama Lake, Norway Eitrhein Bay in situ Physical treatment technology effectively prevents PCBs, PAH and heavy metals in the sediment from entering the water causing secondary pollution; Canada's Hamilton Harbor, Massachusetts, the United States Salen River, Wisconsin, USA Fox River through the release of microorganisms in water bodies, as well as some Chinese scholars The ongoing research on bed biology has yielded good results.
2 eutrophic lake pollution sediment treatment technology classification, characteristics and application
At present, the treatment technology of eutrophic lake sediment can be divided into two kinds: ectopic treatment technique and in situ treatment technique, as shown in the figure:
2.1 ectopic processing technology
Ectopic processing of contaminated sediment mainly refers to the dredging technology and sediment dredging treatment. By hydraulic or mechanical methods to remove pollutants in the lake sediment surface, and then transported to reduce sediment discharge. Generally believed that when the concentration of pollutants in the sediment 2-3 times higher than the background value, which need to consider dredging.
At present, dredging technology has been applied worldwide, generally using dredgers. There are many modern dredgers, which are divided into more than 20 categories in three broad categories. There are over 1,800 domestic or imported dredgers in our country, which handle different contaminated sediments. China's Dianchi Cao Hai, Chaohu Lake in Anhui Province, Hangzhou West Lake, Sweden's Trummen Lake, etc. have adopted the technology. Many scholars have carried out relevant research and discussion on the advantages and disadvantages of dredging, and their opinions are not uniform. However, dredging as an important method of removing pollutants from lake ecosystems is worth promoting.
2.2 in situ processing technology
In situ treatment of contaminated sediment means that physical, chemical or biological processes are used in lakes to reduce the volume of contaminated sediments, reduce the amount of contaminants or reduce the solubility, toxicity or migration of pollutants and reduce the release of pollutants Sediment pollution remediation technology. According to their different principles, can be divided into: in situ chemical treatment, in situ physical treatment, in situ biological treatment and in situ ecological treatment of four.
3. Ecological restoration is the only way to solve the problem of lake sediment pollution
Many domestic scholars have compared the current sediment treatment technology, most people think that, because the lake sediments contain a large number of bio-available organic matter, biological life and metabolic activity can be biodegradable pollutants, while promoting their own Grow. Therefore, for a long time, sediment pollution biological treatment technology has received widespread attention and research, such as the current study of microbial degradation of nitrogen, animal and plant accumulation of heavy metals, plant phosphorus enrichment. However, the single biological treatment technology, because of its strong pertinence, can only work well for some pollutants and can not completely solve the problem of sediment pollution in the lake. It can not play a good role in the biological treatment of heavy metals and phosphorus Therefore, it is necessary to pass through the material circulation of the entire ecosystem to finally bring these pollutants away from the lake system and purify the lake as a whole. Therefore, sediment ecological restoration technology will be eutrophic lake sediment pollution control must pass. However, compared with other treatment technologies, the sediment ecological restoration technology has long cycle and slow response, which is its shortcoming. According to the national conditions of our country, we think that combining different sediment disposal technologies and bioremediation technologies for the different polluting lakes, taking into account the short-term benefits and long-term benefits, the ultimate goal of ecological restoration is to solve the problem of lake sediment pollution.