Study On Augmentation Of Bioremediation In The Constructed Wetland Of Mengqing Garden

Constructed wetland as a kind of dirty water treatment system is an artificial building which has wetland properties. Physical, chemical and biological degradation are the ways to purifying the dirty water. Due to benign eco-friendliness, energy-saving and low operating costs, it is attracting attention in the bioremediation of polluted water.As a crystallization of synthesized treatment of Suzhou River, Mengqing Garden based on the ecological rules. Ecological restoration technique and aquatic ecosystems are used to improve the water quality and the landscape. As one of the key parts in the Mengqing Garden, the constructed wetland was studied in this text. This work is subproject of "Improvement technology and case study of Shanghai city water environment" (Project No: 2003AA601020). The augmentation of bioremediation of the microbe, reed and zoobenthos were studied in the work, as well as mechanisms of the bioremediation studied. The conclusions are the technical basement and theory reference to the applying of the constructed wetland in bioremediation, which were drawn as follows:1) The degradation effect of C, N and P in the Suzhou River by different commercial inocula were studied. The result indicated the inocula are efficiency to the pollutions. High solution microbes to the Suzhou River were achieved after 3 weeks Culturing and the ability to degradation the COD of Suzhou River is one times higher than the controlled group in 12h, the remove ratio of the ammonia could be 88.4%.2) In mesocosm experiment, the degradation rate of ammonia is 30% in test group and 20% in controlled group per year while the TN and TP have 24%, 23% in test group and 20%, 23% in controlled group, which indicated the affective of the inocula.3) With the contribution of root oxygenation, the soil oxidation-reduction potential (ORP) maintained at the +100mV in rhizosphere, while the non-rhizosphere maintained negative. The respiration intensity in the rhizosphere decreased from 0.76 CO₂mg/g·d to 0.55 CO₂mg/g·d from April to July in the rhizosphere while non-rhizosphere maintained at 0.50 CO₂ mg/g·d. By the contribution of root oxygenation, the rhizosphere effects of microorganism are obviously. The ratio of bacteria, fungi and actinomyces in the rhizosphere and non-rhizosphere (R/S) are 11.8, 11.9 and 11.7. The R/S ratio of nitrobacteria, Nitrosomonas and denitrifying bacteria were 14.1, 17.3 and 22.4. The result proved the reed had positive affect to the development of the microorganism.4) Study of biomass and nutrition contents of the reeds showed that the aboveground part of the reeds grown from March to November, the maximum biomass was 2980.8g/m² which showed in the end of October. The nitrogen content of the aboveground reached the maximum in autumn, which was 1.64%, The phosphors content of the aboveground was similar to that of the nitrogen, which have reached the maximum 0.23% in autumn. According to the biomass of aboveground and the nitrogen and phosphors contents, the best time for the harvest was in the end of October. By then, the removing of the nitrogen will reach 485.7kg/hm² and 67.9 kg/hm² of phosphors with the harvest of the plants.5) The batch test of the turbidity degradation on zoobenthos (spiral shell and mussel) shows that spiral shell and mussel could significantly reduce the turbidity of the Suzhou River. The test group could reduce the turbidity to the stable state in only 4 hours. The degradation effect of spiral shell was better than that of the mussel. The result of the dynamical test shows that the average turbidity degradation rate was 66.0%-83.2% of the test group under the same HRT condition, which was better than the controlled group. When the HRT was 2.5h and the density of spiral shell was 400-800/m², the turbidity degradation rate could be above 35%. The density of the spiral shell of 400/ m² could be the best for the system considering the cost of the project. When the density of the spiral shell was 800/ m², the best HRT was 6h and the turbidity degradation rate could be 68%. he results shows that the spiral shell could play a big role in the Mengqin Garden.6) The result of the microbe's community structure shows, the microbe quantity of the rhizosphere is higher than the non-rhizosphere, and the bacteria quantity could be 100 times more than the non-rhizosphere in summer and autumn. The use of inocula increased the microbe quantity of the mesocosm, obviously higher than the controlled group.7) The research of the seasonal distribution of nitrogen and phosphorus in wetland system indicates that the nitrogen fixation of algae doesn't play an important role in the wetland of Mengqing Garden. It also indicates that influent is the major nitrogen resource of the system. Nitrification-denitrification is the main path of denitrogenation in the wetland. And it removed 71.86g/m² N, which was 76.41% of total denitrogenation in spring. The reeds remove 34.57g/m² which were 39.38%. The adsorption of sediments is the weakest, which takes about 10%. In the removal of phosphorus, the adsorption of the sediments is the main path of phosphorus removal which remains more than 50% constantly. The highest is 92.08% in spring, and lowest is 57.81% in autumn. The absorption of plants changes apparently as the seasons. It takes more than 20% of the removal of total phosphorus in summer, autumn and winter.