Study On Removal Efficiency Of Typical Organic Compounds In Large Wetland In Liao River Protected Area

Constructed wetland is a kind of sewage treatment technology which has been paid more attention and widely used all over the world in recent years.A large number of large-scale constructed wetland projects were built at the entrance of the main tributary river and stream of the Liao River,aiming at reducing the pollutants in the tributaries and improving the pollution situation of the Liao River.In order to find out the migration and transformation and distribution characteristics of pollutants in the tributary estuary wetland engineering in Liao River,this paper conducted the long-term water quality monitoring and research for the four exemplary constructed wetland engineering in the middle and upper reaches of the Liao River and the pilot engineering of the Panjin wetland in the lower reaches of the Liao River.The temporal and spatial distribution characteristics of conventional pollutants in wetland engineering were studied.The method of Gas Chromatography Triple Quadrupole Mass Spectrometry(GC-MS/MS)were established to accurately measure the three typical organic pollutants(organophosphorus pesticides,organochlorine pesticides and polychlorinated biphenyls).The pollutant removal efficiency of constructed wetland was calculated,and the Nemero comprehensive pollution index method was used to evaluate the water quality of Wetland,the following conclusions were drawn:The concentration of COD and NH3-N in the Liao River wetland engineering was higher in the tributary inlet.Via the internal control and purification of the wetland,the concentration of COD and NH3-N decreased in the wetland exit and the content of sampling points in the upstream was lower than that in the downstream and had the decreased trend with the passage of time.The content of pollutants in some sampling points fluctuated during the spring and summer seasons.On the whole,the COD content at the exit of the wetland engineering basically reached << Surface Water Environmental Quality Standard >>(GB3838-2002)V grade water quality standard throughout the year,while NH3-N pollution was slightly serious in the first half of the year.Seven kinds of organophosphorus pesticides,nineteen kinds of organochlorine pesticides and nineteen kinds of polychlorinated biphenyls were detected by GC-MS/MS method.The content of total organophosphorus pesticides was NF-849.187ng/L and the main components were monocrotophos,parathion and ethyl-p-nitrophenyl phenylphosphonothioate(EPN).The content of total organochlorine pesticides was NF-2398.802ng/L and the main components were LPHA-BHC\alpha,heptachlor epoxide(isomer B),endosulfan sulfate,endrin-aldehyde,endrin-ketone,BETA-BHC\beta six organochlorine pesticides.The total content of PCBs was 3.221-329.081ng/L,the main components were PCB31,PCB66,PCB170,PCB180,PCB206.In winter,the contents of organophosphorus pesticides and organochlorine pesticides were higher and had certain fluctuation change in sampling points over time.In spring,the content of organophosphorus pesticides and organochlorine pesticides decreased significantly compared with winter.The content of the organophosphorus pesticides declined faster and had more stable fluctuations.As a whole,the content of organophosphorus pesticides and organochlorine pesticides was higher in upstream,great fluctuations in Qixing wetland and lower in downstream in the winter.In spring,the content decreased significantly compared winter especially organic phosphorus pesticide.The content decreased in upstream,increased in the downstream.There were many kinds of PCBs in the sampling point in spring,but the content was low.The content of PCBs was less than limiting value 20ng/L << Surface Water Environmental Quality Standard >>(GB3838-2002)in the majority of sampling points.PCBs content in the Qixing wetland and Panjin wetland was high in April and exceeded the standard limit in some sampling points.The change of PCBs content was stable in the middle and upstream and fluctuated in the downstream,diminishing effect of the wetland on PCBs was not obvious.Taking QiXing wetland as an example,the amount of pollutant removal during non freezing period in wetland was calculated,and the total removal rate of COD was about 52.61 t,the removal rate was 29.56%,the total removal rate of ammonia nitrogen was about 7.36 t,and the removal rate was about 46.34%.The total removal of OPPs is about 1.44 g,the removal rate is about 15.34%;the total removal of OCPS is about 169.86 g,the removal rate is about 71.05%;the total removal of PCBs is about 22.19 g,the removal rate is about 19%,in April and May.The Nemero comprehensive pollution index method was used to estimate the water quality of wetland projects,of which 44% were clean water and cleaner water,and slightly polluted water accounted for 31%.