Study On Purification Of Low-polluted Water Of Erhai Lake By The Buffer Zone

With the introduction of new ideas of lake treatment in China and the enhancement of lake management,the problem of low-polluted water is getting more and more attention.The control of low-polluted water is another new challenge after the point pollution source and non-point pollution source of lake.Low-polluted mainly comes from three different sources:agricultural runoff,urban surface runoff and discharge from water treatment plant.Low-polluted water caused a great threat to Erhai Lake,we need to take an effective way to management,the buffer zone is an effective way.In this study,constructing different types of pilot scale test of buffer zone to test the effect of purifying low-polluted water.According to the results of test,calculating the optimal width.Experimental site is located in the town of Dali and south bank of Zhong He Rivulet(25°42'16"N?100°10'19"E),about 3km away from the Erhai Lake area.The pilot scale test include ecological gravel buffer zone,aquatic plants buffer zone and plenty types of plants buffer zone.(1)Ecological gravel buffer zoneFour ecological gravel buffer zones are constructed with a layer is set uniformly under each zone with gravel.Three of the four zones are planted with cattail,scripus tabernaemontani and bulrush respectively,and the remaining belt is set as a blank controller without vegetation,the destination is explore the effect of different plants on the removal of low-polluted water.Water for examination is agricultural runoff of low-polluted water,which is divide by the sewage pipe.The water samples which are taken along the point of the buffer zone should be analyzed.According to the analysis results,using the SPSS 18.0 to calculate the optimal width.The results show that:ecological gravel buffer zone could reduce the TN,TP and CODcr in ecological gravel buffer zone effectively,the removal efficiency from high to low are cattail,scripus tabernaemontani,bulrush and blank controller;effect of vegetation selection on TN removal efficiency is significant.When average removal rate of TN is 80%,the optimal width is different for each zone:3.9m for cattail,4.7m for scripus tabernaemontani,6.3m for bulrush,and 8.6 m for blank controller,when average removal rate of TP is 80%,3.9m for,4.9m for scripus tabernaemontani,10.8m for,and 96.1 m for blank controller,and when average removal rate of CODcr is 80%,the optimal width is different for each zone:4.8m for cattail,7.2m for scripus tabernaemontani,9.7m for bulrush,and 11.5m for blank controller.Which indicated that the ecological gravel buffer zone could effectively save the land.Could decide the optimal width according to the reality,so that make it has good removal effect on the TN,TP,CODcr.(2)Aquatic plants buffer zoneThree aquatic plants buffer zones are constructed with a layer is set uniformly under each zone with soil from Dali that covered with a certain thickness of water.Three of the two zones are planted with nymphoides peltatum and balamus respectively,and the remaining zone is set as a blank controller without vegetation.Adding a certain amount of nutrients to the pool to prepare low concentrations of sewage,whose concentrations are the same as urban surface runoff of low-polluted water.The water samples which are taken along the point of the buffer zone should be analyzed.According to the analysis results,using the SPSS18.0 to calculate the optimal width.The results show that:aquatic plants buffer zone could reduce the TN and TP in aquatic plants buffer zone effectively,the removal efficiency from high to low are nymphoides peltatum,bulrush and blank controller;effect of vegetation selection on TN removal efficiency is significant.When average removal rate of TN is 80%,the optimal width is different for each zone:8.4m for nymphoides peltatum,9.6m for scripus tabernaemontani and 12.5m for blank controller,when average removal rate of TP is 60%,the optimal width is different for each zone:11.6m for nymphoides peltatum,12.1m for scripus tabernaemontani and 6194.1m for blank controller.Which indicated that the aquatic plants buffer zone could effectively save the land.Could decide the optimal width according to the reality,so that make it has good removal effect on the TN and TP.The aquatic plants buffer zone can be used to deal with low concentrations of low-polluted water from Erhai Lake basin.It can also be adopt to purity tail water from ecological gravel buffer zone and make it cleaner.(3)Plenty types of plants buffer zoneThe reasonable allocation of different types of plants can appropriately improve the removal of low-polluted water.Therefore,according to different plant species,10m plenty types of plants buffer zone are constructed which include macrophanerophytes and shrub buffer zone that is planted redwillow and photinia fraseri,sward buffer zone that is planted clover and aquatic plants buffer zone that is planted nymphoides peltatum,bulrush and edible seaweed.The results show that:plenty types of plants buffer zone could reduce the TN and TP,the removal efficiency from high to low are macrophanerophytes and shrub buffer zone,sward buffer zone and aquatic plants buffer zone.Because of difference of plant species,plant density and filler,don't calculate the optimal width.Through the experiment and analysis,Through the above test analysis,it can provide suggestions for the selection of the buffer zone in Erhai Lake.The optimal width can provide some parameters for the implementation of the buffer zone,and save the land.