Study On Eco-protecting Technology Of Water Quality In Green Residential District

With the development of the resource-saving and environment-friendly society and the spread of the career of building energy saving, the idea of green building and green residential district has been enjoying popular support and receiving more and more attention. This article aims at the demand of the green residential district for the water quality and eco-landscape, undertakes the research of eco-protecting Technology of water quality for three water quality, focused investigates the disposal efficiency of seven construed wetland with different plant against domestic sewage, screens out plants fit for the territory of Chongqing, investigates the starting characteristic of Gravel trench and its purification mechanism, purification ability and operation characteristics for the roof runoff, surveys water quality variation of landscape water under natural circumstance and that of former, medium and later range of rainfall, and achieves the best optimum working condition for the application of the effluent of grey-water with high quality disposed by constructed wetlands to landscape water. The chief conclusions by research are as follows:①The research for the screening out of plant fit for the constructed wetlandsThrough the detection of the water quality of the constructed wetlands effluent after the 1st, 2nd, 3rd, 4th, and 7th day after inflow, the removal rate of each plant wetland against COD,TP,TN and NH3-N enlarges along with the prolonging of the time, that is, the largest figure of removal rate appears on the 7th day. The research of removing COD from sewage shows that the water quality of the six plant wetlands effluent meets the Class-V of the standard of water quality (≤40mg/L) of environmental quality standards for surface water (GB3838-2002) other than reed one on the 7th day, and the result of calla wetlands is better than others. The removal rates among the seven plant wetlands against TP are different. The TP concentration of effluent of calla reaches Class-IV of the water quality (≤0.3mg/L), and the canna's reaches that of Class-V(≤0.4mg/L), while the rest plant wetland fails to reach Class-V thereof. Despite that the best result of removing NH3- N appears in canna wetland and reed wetland, they fails to reach Class-V of the standard of water quality (≤2.0mg/L).The result of the research shows that the best four plants to remove the pollutants are windmill grass, canna, reed and calla. They are all green flowers and plants to purify the sewage and beautify the environment when used as wetland plant. Since different plant has different effect to different pollutants, such as canna and calla removes TP well, and reed has the well removal against TN, the appropriate plants can be chosen in accordance with the different nature of the pollutants to build appropriate plant communities so that the purification of the wetland disposal system against sewage shall be improved.②The approval test study of the effectiveness of disposing the roof rainfall by gravel trenchThe experiment of purification effectiveness of gravel trench shows that the remove rate of system may reach 8%～67%against COD, 12%～46% against TP, 8.45%～46.7% against ammonia nitrogen, 46%～67% against turbidity. The removal rates against the pollutants descent obviously along with the increase of the flow of rainfall, among which the downtrend of the removal rate of COD is most obvious. For the inflow with light concentration, the effectiveness of removing runoff pollutant by gravel trench is well, and the effluent of experiment is superior to Class-V of surface water quality. For the inflow with high concentration, in spite that the removal rate against pollutant is high, the absolute quantity of the concentration of water pollutant is not low.③The study of the effectiveness of landscape water quality protectionThe result of the detention for the variation of landscape water quality shows that the reason for the rapid water degradation is its lack of self-purification capacity so as to result in the high concentration of ammonia nitrogen and total phosphorus. Where hard disposal is also accounted, eutrophication of the water especially conversion to phosphorus is caused. Because of the short of self-purification capacity, the function of microbe is not obvious; especially when the nutrition is disproportion, the water trends eutrophication more. Properly deepen the water may enhance the self-purification capacity. The deep of the water is benefit for the growth of anaerobe, and the self-purification capacity shall be enhanced accordingly. Another reason for the inferior of the water quality is liquidity shortage so that dead space is easily caused. When the water is in the state of non-flowing, the dissolved oxygen would reduced, which is bound to lead to smelly black issues, and further brings the water bloom.When the hydraulic loading wetlands reaches 0.15m3/m2·d, the landscape water quality changes moderately, after 8th day, the content of COD is inferior to Class-III of environmental quality standards for surface water, after 10th day, the content of COD is inferior to Class-IV of environmental quality standards for surface water; after 4th day, the content of TP is inferior to Class-III thereof , after 8th day, the content of TP is inferior to Class-IV, after 12th day, the content of TP is inferior to Class-V; after 4th day, the content of TN is inferior to Class-II of environmental quality standards for surface water , after 8th day, the content of TN is inferior to Class-III of environmental quality standards for surface water, after 10th day, the content of TN is inferior to Class-IV of environmental quality standards for surface water; after 8th day, the content of NH3-N is inferior to Class-II of environmental quality standards for surface water, after 10th day, the content of NH3-N is inferior to Class-III of environmental quality standards for surface water. Life cycle of water extends, and color, smell and other sensory characteristics are easy to accept. 0.15m3/m2 ? d can be considered as the best wetland conditions.Analysis upon the variation of the former, medium and later range of rainfall shows that concentrations of kinds of pollutants carried by roof runoff of rainfall is well above the landscape, in which N, P nutrients in the water is one of the major sources of pollution.The results of this article of research will provide technical support and reference for the designs for green residential water resource utilize system, which shall have great practical significance.