Study On Effect, Mechanism And Application Of Aquatic Macrophytes-rhizosphere Microorganisms System On Water Purification

At present, the environment of lakes in the country is worryied. In recent years, due to the development and utilization of water resource in an irrational condition, more and more waterbody becomes eutrophication with rapid population growth and economic development. It is reported that eutrophic and extremely eutrophic lakes take up 66% and 22% respectively in China. More than 83.5% water area became eutrophic in Taihu Lake Basin. At home and abroad, the algae outbreak in Taihu Lake on May 29, 2007 caused widespread impact. How to control eutrophic waterbody, reduce nutriment and resume the function of waterbody have become the focus of global environmental problem.The previous study indicated that some hydrophytes and microorganisms could purify waterbody well. Thus, our experiment studied on the effect of different ecosystems of both macrophytes and microorganisms on water purification.(1) In the first indoor experiment, Oenanthe javanica DC. was taken as experimental material. We set up two grads with five concentrations for every grad of each total phosphorus (TP) or nitrogen (TN) to study the change of nutriment concentration and rhizobacteria. The results show that TN played a direct role in promoting the number of rhizobacteria. The rhizobacteria could grow fast when the TN was enough and more. Overall, their number reached the top on the 14th day. In the ecosystem of macrophytes and microorganisms, nitrogen was mainly removed by rhizosphere bacteria, while phosphorus was mainly removed by plant aborbing and the rhizosphere phosphours bacteria acted some. For ecological restoration, Oenanthe javanica DC. could be collocated in eutrophic rivers or shallow lakes.(2) In the second indoor experiment, Veliveria zizanioides, Eichhornia crassipes, Oenanthe javanica DC. were taken as experimental material. We set up three concentrations of nitrogen (TN) with total phosphorus (TP) constant to study the change of nutriment concentration, plants biomasses and rhizobacteria. The results show that these three kinds of aquatic plants acted differently in removing TN and TP. And one plant could have optimal effect under the three concentrations and promote the growth of rhizobacteria. In comparison, Oenanthe javanica DC system. had high absorptive capacity for high concentration of TN, while Eichhornia crassipes system had high absorptive capacity for high concentration of TP. The Veliveria zizanioides and Oenanthe javanica DC. could tolerate the cold environment while Eichhornia crassipes could tolerate hot environment. Thus, they could be collocated in eutrophic rivers or wetlands for landscaping with some income. Thus, it was important to study the effect of Veliveria zizanioides, Eichhornia crassipes, Oenanthe javanica DC. on water pollution with practical application value.(3) The field test of the Demonstration Project in Eighteen Bay of Lake Taihu showed that the project could weaken the energy of wave significantly, and the reducted factor of wave height could be about 75%. When the wave continued to flow through the second wave-reducing belt, the wave height was lower less than 1cm. The physical and ecological wave-reducing belt could reduce wind and waves effectively. Furthermore, Veliveria zizanioides growed lush while Eichhornia crassipes and Ipomoea aquatica growed well in the experimental area. The submerged macrophyte Potamogeton crispus could grow withour escaping.