Study On Pollution Characteristics Of Daoshui River In Hong’an County And Remediation Effects By Constructed Wetland

Daoshui River is the tributaries of the Yangtze River which originates from Xin County,Henan Province,with a total length of 163.3km,including 102.8km in Hong’an County.It is the mother river of Hong’an County,a backup water source,and also has vital fuction being used as industrial and agricultural water,urban flood discharge and deal with sewage and satisfy sevice needs of neighbouring residents.According to the“Types of Surface Water Environment Function in Hubei Province”（2000）,the water environment function of the Hong’an section of the Daoshui River is classified into Class III.However,due to the acceleration of urbanization in Hong’an County in recent years,the level of economic development has increased rapidly,but the construction of some supporting environmental infrastructure has lagged behind,resulting in aggravation of water pollution in the Hong’an section of the Daoshui River.Some indicators of the exit section remain high and continue to exceed the standard.It has had a serious impact on industrial and agricultural production and residents’lives in Hong’an County,and to some extent restricted the economic and social development of Hong’an County.This paper takes the Hong’an section of the Daoshui River as the research object,analyzes the pollution source structure and spatial-temporal distribution characteristics of the water quality in the Hong’an section of the Daoshui River through on-site reconnaissance,data collection and water quality monitoring,and proposes targeted ecological restoration measures on this basis.The main results are as follows:1.The concentration range of COD,permanganate index,NH₃-N and TP in the Hong’an section of the Daoshui River are:5.92-50.47 mg/L,1.79-11.92 mg/L,0.06-9.15 mg,0.01-1.71mg/L,there are 8（32%）points in the dry season exceeding GradeШwater quality,6（24%）in the wet season and 3（12%）in the flat water period.The pollution in the flat water period is the lightest,and the water quality in the dry season is the worst.The water quality evaluation was carried out on 13 monitoring sections on the main stream of the Hong’an section of the Daoshui River.In the dry season,the rate of cross-section exceeding the standard was 46%;in the flood season,the rate of cross-section exceeding the standard was 31%;In the flat water stage,the rate of cross-section exceeding the standard was 8%,and Most of the over-standard sections are located in the monitoring section after the inverted river passes through the town area.The main stream of the Hong’an section of the Daoshui River has different levels of exceeding the standard in the three periods of dry,rich and flat.The water quality is the worst in the dry season,the second in the wet season,and the best in the flat water period.2.According to the analysis of pollution source structure,The pollution of the Hong’an section of the Daoshui River mainly comes from urban living pollution,agricultural planting pollution,livestock and poultry breeding pollution,rural living pollution,river dust pollution,industrial enterprises discharge pollution,and total pollutants entering the river.The total amount of pollutants entering the river is:the total amount of COD entering the river is9213.2 tons per year,the total amount of NH₃-N entering the river is 1302.72 tons per year,the total amount of TN entering the river is 2163.17 tons per year,and the total amount of TP entering the river is 396.2 tons per year.From the spatial distribution analysis of pollution sources,in the towns and villages of Hong’an County,the amount of pollutants entering the river in Chengguan Town is the highest,of which COD inflow is 2408.45 tons per year,accounting for 26.14%of the total;NH₃-N inflow is 318.42 tons per year,accounting for24.44%;TN inflow is 487.69 tons per year,accounting for 22.55%,TP inflow is 65.09 tons per year,accounting for 16.43%.3.Vertical upward subsurface flow constructed wetland was used to simulate the treatment experiment.The packing was made of gravel,zeolite and volcanic rock.The experimental results show that the three filler wetlands have good removal effect on COD.The maximum removal rate of COD in gravel packing wetland is 42.48%,that of zeolite filler wetland is 48.42%,and that of volcanic rock filler wetland is 51.70%.Zeolite filler wetland has the best removal effect on NH3-N,up to 86.51%.The maximum removal rate of NH3-N from gravel pack wetland was 58.22%,and the maximum removal rate of NH3-N from volcanic rock filler wetland was 73.02%.The removal effect of TP on volcanic rock filler wetland can reach 47.06%.The gravel filler wetland and zeolite filler wetland have poor removal effect on TP,and the maximum removal rates are only 17.65%and 27.78%,respectively.