Control Of Algal Grouth Through Shading At The Sites Of Drinking Water Sources

With the development of Chinese economy, the eutrophic situation of many lakes and reservoirs which are supplying the drinking water for Chinese people are becoming more and more severe. The water blooms happen to the drinking water sources and threaten the drinking water safety. For example, the Taihu Lake water bloom in 2007 cut off the water supply of the whole Wuxi City and disordered the people's life. In this dissertation, the relationship between the algae growth and the light was studied, and the shading technology was introduced. The core of this technology is to decrease the light intensity, to restrict the photosynthesis of algae, to restrain the growth of algae and control the water bloom.The research shows that the shading technology can reduce the algae concentration in the water greatly in 7 to 9 days. According the test results, the shading technology can decrease the chla concentration from 100μg?L-1 to about 20μg?L-1 in 7 to 9 days; The shading technology can handle the water bloom emergency, and can be utilized before the water bloom to prevent breaking out of the water bloom.1. In the BG-11 culture medium, the light intensity of 4300lx is optimum to the growth of Microcystis aeruginosa; When the light intensity is less than 500lx, the algae growth will be restrained, and the specific growth rate will drop greatly; When the light intensity is less than 120lx, the specific will become minus and the algae concentration become less and less.2. Use the sterilized water sample from the drinking water sources as the culture medium. And the growth of Microcystis aeruginosa will be restrained greatly when the light intensity is less than 500lx, the specific growth rate is -0.13d-1, and the algae concentration will become less and less. The light intensity of less than 500lx can control the algae growth effectively.3. Use the shading net from the market as the shading material. The light intensity under the water can be decreased effectively by this shading material. The light intensity of the surface water can be decreased from 10000lx to 2000lx by shading. The light intensity of more than 80% of the whole enclosure can be decreased to less than 500lx before 9 o'clock in the morning and 3o'clock in the afternoon.4. When the water blooms in the enclosure, the water of the 1.25m deep has the highest chla concentration in a sunny day, and the concentration of the bottom layer is 1.2 times more than the surface layer; The water of the 0.65m deep has the highest chla concentration in a cloudy day, and the concentration of the medium layer is 29% more than the surface layer; After shading the enclosure the chla concentration of the surface water is 60% more than the bottom layer. The shading can change the distribution of the microcystis effectively.5. In 7 days the chla concentration in the enclosure was decreased from 176.9μg?L-1 to 21.4μg?L-1 during the first shading experiment; In 9 days the chla concentration in the enclosure was decreased from 97.8μg?L-1 to 33.2μg?L-1 during the second shading experiment. The shading technology can restrain the algae photosynthesis, decrease the biomass and control the water bloom effectively.6. In the pilot test of the shading technology, the chla concentration, turbidity and COD of the water dropped greatly after 9 days shading. The removal rate of the chla concentration, turbidity and COD were 73.9%, 67.3% and 77.7%. The pilot test approves the feasibility of the shading technology. A new algae control method can be introduced according the test: decrease the light intensity of the water around the water intake in the water source through the engineering means, the algae photosynthesis can be restrained and the algae concentration can be decreased to a low level in a short time.7. Use the shading net from the market as the shading material, and use the bamboo or the plastic foam to support the material net. This shading structure can float on the water and resist the wind; Planting the water plants on the material net can increase the shading effect, remove the N, P in the water and beautify the water environment. The shading structure and the water plants can combine to the ecological shading technology.