Study On The Assessment Of Water Quality And Water Environmental Capacity Of Shifosi Constructed Wetland

As a unique ecological system,constructed wetland has the advantages of good effluent purification effect and low cost,but it can not eliminate unlimited amount of sewage.Excessive pollutants will degrade the wetland or even make it lose the function of wetland.In this study,Shifosi Constructed Wetland was chosen as the research target.It uses Bayesian method with Entropy Based-Weight and BP neural network method to evaluate its water quality to understand the current status of constructed wetland upstream water and its inside water quality,and then uses the residual modified GM?1,1?predicts the water quality of Shifosi constructed wetland to understand its incoming water and inside water quality development and changes.Then according to the water quality target which determined by the functional positioning of the Shifosi constructed wetland water environment,calculates the water environment capacity,and finally,To ensure the efficient operation of the Shifosi Constructed Wetland Ecosystem and play a good role in purifying water,some water environmental protection are put forward.The main research results are listed as following:?1?According to the water quality evaluation results of the Shifosi Constructed Wetland from 2009 to2015 by Bayesian method with Entropy Based-Weight and BP neural network method,There are relatively objective and credible result on both the two methods,indicating that both methods are Effective and feasible.The outlet water quality of the two evaluation methods is basically better than the upstream water quality.It can be seen that the water quality of the Liaohe River has been significantly improved after passing through the constructed wetland,the water quality was purified effectively by Shifosi Constructed Wetland.The evaluation results showed that the outlet water quality was grade II or III from 2009 to 2015.The water quality during the flood season was better than the non-flood season,the upstream water quality during the non-flood season in 2009 and 2010 was IV-V,the upstream water quality during non-flood season in 2013,2014 are also poor and the result grade were III-V.The remaining years results are better which can reach grade III.Although the upstream water quality of the non-flood season is relatively poor in recent years,the outlet water quality can reach to grade III or above after the Shifosi Constructed Wetland purification??2?The prediction of the water quality of the Shifosi Wetland constructed wetland with relatively serious COD_Cr,ammonia nitrogen,total phosphorus,and total nitrogen as the study object.Due to the short monitoring time series and insufficien monitoring data,this paper used grey system theory to establish one-dimensional time series prediction model?Grey Residual Error modified GM?1,1?model to predict COD_Cr,ammonia nitrogen,total phosphorus and total nitrogen.Through modified Residual,the model accuracy judged by Posteriori difference can reach the qualified or above.The paper predicted concentration of COD_Cr,ammonia nitrogen,total phosphorus and total nitrogen in the next three years and have certain guiding values.?3?Based on the water quality objectives of Shifosi constructed wetland,the water environmental capacity of Shifosi Constructed Wetland was numerically simulated preliminarily.On the condition that the water quality target is III level water quality,the water environmental capacity of Shifosi Constructed Wetland should be:COD_Cr is 32591t/a,NH₃-N is 1629t/a,TP is 93t/a and TN is 1861t/a.At present,the loads of COD_Cr,NH₃-N,TP and TN flowing into constructed wetlands are 18704 t/a,1422 t/a,49.61 t/a,and 1979t/a.Comparing the calculation result of the environmental capacity,the remaining capacity of COD_Cr is13887t/a,the remaining capacity of NH₃-N is 207t/a,the remaining capacity of TP is 43.39t/a,the remaining environmental capacity of TN is-118t/a whose exceeding standard rate is 6%,so it need to be reduced load.?4?After fully understanding the water quality of the Shifosi Constructed Wetland and its own water quality status and changes in water quality and analysed on water environment capacity,this paper recommends the measurements to protect the water environment and countermeasures of pollution control in Shifosi Constructed Wetland.The scientific and reasonable implementation of these measurements will contribute to the conservation and improvement of water environment.