| With the rapid development of our country's economy, the demand of industry and domestic sewage is increasing, thus the water pollution become serious day by day. Kinds of low polluted water such as treated effluent from municipal and industrial water treatment plant, treated effluent from farming, rural domestic sewage, rain and farming runoff, attracted people's widespread attention gradually due to the large amount. Accordingly,the advanced treatment and reuse have gradually become the focus of people's attention.In this study, low polluted water is taken as the research object, and the following research has been carried out. Firstly, based on literature summary, laboratory and pilot test, an first-order degradation database of common plants for low polluted water in different seasons was constructed,and it can be used to correct the model parameters. Secondly, this study verified that QUAL2K model canbe used to design the ecological engineering and select the best scheme. Also, a specific scheme was designed in this reasearch. In addition, project performance evaluation system was constructed. Through case evaluation, problems and characteristic of ecological engineering in domestic was summarized, and suggestions for improvement was put forward. The following is the main research content and results summary.Through 2013-2014 year, this study sampled and monitored the typical low polluted water, and analyzed its characteristics. It was found that TN is 2-7 times and TP is 0-0.65 times high than the V standard Environmental Quality Standard for Surface Water, of which NO3--N and OP are the major components. There is a common problem of carbon source insufficient in the effluent of wastewater treatment plant.Based on literature summary, laboratory and pilot test, an first-order degradation database of common plants for low polluted water in different seasons was constructed, and it can be used to correct the model parameters. Meanwhile, plants with good purification efficiency in common plants was selected. In summer, including emergent plant:Canna, calamus, reed and Thalia dealbata, Floating leaved plant Nymphaea L.,Submerged plant:Ceratophyllum demersum L. and waterweed, Ecological purification material is biological rope and ecological grass, their maximum first-order degradation coefficient is up to 0.75 for TN and 0.59 for TP. In winter, including emergent plant:calamus and cress, Submerged plant:Ceratophyllum demersum L. and waterweed, Ecological purification material is biological rope and ecological grass, their maximum first-order degradation coefficient is 0.20 for TN and 0.18for TP. Through the analysis of functional microorganisms, we found that the main functions of the low polluted water are Nitrospira, Flavobacterium, Acidovorax, Pseudomonas, Hydrogenophaga, Thiobacillus, Dechloromonas, etc..In ecological purification scheme design, ecological engineering in Caoqiao WWTP was taken as an example, a QUAL2K numerical model was constructed, and the model was verified by the monitoring data from 2013 to 2014, thus, QUAL2K model was validated for scheme design. At last, the optimal combination of ecological purification in different seasons was selected. Combination with the lowest pollution index in summer, spring/autumn and winter were emergent plant(E)+biological rope(B),E+submerged plant(S)+B, and S+B, respectively. The removal rates for TN and TP in different seasons were 32.48-37.33% and 31.63-39.86%(summer),14.12-33.61% and 17.74-23.80%(spring/autumn), and 14.13-18.03% and 10.05-12.75% (winter).In order to make the annual TN and TP water quality indicators reach the surface water V class standards, layout density and the hydraulic retention time in spring,autumn and winter should be improved. The simulation results of QUAL2k model showed that in spring and autumn, the hydraulic retention time and the density should improved to 2 times and 3 times of the original, namely layout of Canna Ceratophyllum demersum and biological rope should be:17.4kg,7.9 kg and 72.5 meters per square metre of water area; in winter, the hydraulic retention time and the density should improved to 3 times and 4 times of the original, namely layout of waterweed and biological rope should be:24.1 kg and 96.6 m per square metre of water area.Through the selection of appropriate indicators, this study constructed a performance evaluation index system coupled with artificial neural network model to ecological purification.The system has two characteristics:Firstly, this study constructed a water environment quality standard for low polluted water, and normalized eutrophication index in different scheme with the fuzzy neural network (FNN); Secondly, this study fit a curve between the construction cost and wetland volume, and gives experience formula which can be used for the rapid estimation of investment projects. Based on the constructed index system, the research collects the data of 15 typical ecological engineering for low polluted water and makes an evaluation of them. Then, the characteristic and problems of the ecological engineering for low polluted water has been summarized.It is common that the engineering gain a good enviromental benefits, but the economic benefits are very low; engineering investment is quite high,while the removal rate is quite low; poor management lead to a low recreation value and investment efficiency. At last, this study also gives suggestions for improvement. As to the poor economic benefits, the government should construct the mechanism, operators should improve awareness, enterprises make sales network, and scientific research institutions strengthen technical transformation. With the changing of four parts, the economic benefits of ecological project will be improved. As to the investment is not proportional to the water quality improvement, it needs to play the advantage of numerical simulation, and make quantitative calculation to improve the scientificity and accuracy of ecological engineering design. As to poor management, the operators should focus on the propaganda and guidance, and make the wetland as a township residents'leisure gathering places. Thus, the operator will be forced and encouraged to improve their management and maintenance, and eventually form a virtuous circle. |
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