Study On The Enrichment And Release Of Nitrogen And Phosphorus From Internal And External Sources In Ecological Ditch System

Ecological ditch as a water pollution treatment technology which has the advantages of small land occupation,low cost,easy management,good treatment effect and certain landscape effect.In recent years,it has been widely used in the treatment of non-point source pollution by researchers,but the improvement of ecological ditch technology and its application in the prevention and control of internal and external sources pollution system are rare.Based on the research results of ecological ditch at home and abroad,and combined with the landscape effect of wetland basin,this study used slag,waste brick and zeolite as the combination matrix according to the mass ratio of 3:1:1,and Bulrushes,Scirpus validus,Iris,and Lythrum salicaria,which possess excellent cold resistance and landscape effect,are used as water treatment plants to build an ecological ditch system with the ability of swallowing and spiting sediment.And ecological ditch system is applied to the study on the treatment of internal and external source pollution in wetland drainage ditch which can provide significant reference for controlling eutrophication of rivers and lakes and black and odorous water.During the period from May 10 to September 30,2019,three parameters including different types of ditches（blank ditch,plant ditch,substrate ditch and ecological ditch）,different hydraulic retention time（0,6,12,24,48,72,96,120 h）and different influent nitrogen and phosphorus concentrations（low concentration,medium concentration and high concentration）were operated,the effect of ecological ditch system on the enrichment and release of nitrogen and phosphorus from internal and external sources was studied,and the microbial community structure in ecological ditch system was analyzed.The main results are as follows:（1）Through the operation of different types of ditches,different hydraulic retention time and different influent nitrogen and phosphorus concentrations,the ecological ditch has the best interception effect on nitrogen and phosphorus,and the average removal rates of nitrogen and phosphorus in low,medium and high influent water were TN:78.93%,69.82%,58.61%,TP:90.31%,84.47%,76.71%,respectively.（2）During the period of operation and monitoring from May to September in 2019,the operation hydraulic load of the ecological ditch system is 0.017 m³·m^-2·d^-1,and the daily water treatment capacity is 3.216 m³.On the time scale,the removal rates of TN and TP pollutants in the inlet and outlet water were 29.26～72.71%and 27.78～75.68%respectively,and the TN concentration in the outlet water in June,July and September was basically lower than the surface water environmental quality class V standard;The effluent TP concentration in May,June and September was lower than the surface water environmental quality class III standard,and in July was lower than the surface water environmental quality class II standard.On the spatial scale,the average concentrations of TN were 4.59,3.95,3.51,2.92and 2.41 mg·L^-1 and the average concentrations of TP were 0.27,0.23,0.2,0.16 and 0.14mg·L^-1 at 0,3,6,9 and 12m in ecological ditch system,respectively.The average removal rates of TN and TP were 55.47%and 55.22%,respectively.（3）During the whole operation period of the ecological ditch system,the daily average uptake of nitrogen and phosphorus in the external water was about 14.46 g·d^-1 and 0.96g·d^-1,respectively.The daily average accumulation of nitrogen and phosphorus in substrate and plant was about 2.02 g·d^-1,10.71 g·d^-1,0.70 g·d^-1 and 8.43 g·d^-1,respectively.The daily average release of nitrogen and phosphorus from endogenous sediment was about-1.73 g·d^-1 and 8.17 g·d^-1,respectively.High throughput sequencing showed that Proteobacteria,Actinobacteria and Nitrospira were the main denitrification bacteria,Arthrobacter and Sphingomonas were the main nitrifying bacteria,and Gemmobacter,Paracoccus and Sphingomonas were the main denitrifying bacteria.