Evaluation Of Nitrogen And Phosphorus Purification Efficiency Of Constructed Wetland And Pond Recycling Water Culture System

The combination of pond circulating water culture and constructed wetland is a new idea of green culture.In this experiment,the composite vertical subsurface flow constructed wetland-pond circulating water culture system was used to construct the constructed wetland-pond circulating water culture system.Through the research on the migration and transformation of nitrogen and phosphorus and othersourceelements in the culture system,the purification effect of nitrogen and phosphorus pollution in the whole process of culture system was evaluated,which provided some data reference for optimizing the constructed wetland-pond circulation model.The main findings are as follows:During the previous four months,Average total nitrogen concentration of pond,ditch,constructed wetland inlet and constructed wetland outlet was 8.19mg·L^-1,8.20mg·L^-1,7.83mg·L^-1,5.31mg·L^-1,respectively Compared with pond concentration,The average purification rate of total nitrogen was 43%,The average removal rates of ammonia nitrogen（NH₃-N）,nitrate（NO₃^--N）and nitrite nitrogen（NO₂^--N）were 62%,58%and 61%respectively;Average concentration of total phosphorus was 0.194mg·L^-1,0.185mg·L^-1,0.179mg·L^-1,0.0648mg·L^-1,The average purification rate of total phosphorus was 66%,average removal rate of orthophosphate(PO₄^3--P)was 47%.For total phosphorus（TP）content,High proportion of orthophosphate(PO₄^3--P),More than 40%.The contents of nitrogen,phosphorus and nutrients in the inlet of pond,ditch and constructed wetland decreased in turn,Compared with the pond,the total nitrogen concentration of constructed wetland outlet decreased significantly,During the breeding cycle,The removal efficiency of nitrogen and phosphorus nutrients in pond water is stable,in accordance with the Fisheries Water Quality Standards of the People’s Republic of China.The contents of total nitrogen（TN）and total phosphorus（TP）increased slowly in various functional units（deposits of ponds,ditches,artificial wetlands）at different periods.The average mass fraction of total nitrogen（TN）in ponds,ditches and water outlets was 683.6 mg·kg^-1,678.1mg·kg^-1,701.3mg·kg^-1,825.4mg·kg^-1;and the average mass fraction of total phosphorus（TP）was 93.7mg·kg^-1,104.6mg·kg^-1,94.5mg·kg^-1,110.6mg·kg^-1.The total nitrogen and total phosphorus concentration in the outlet is the highest,and the adsorption and precipitation of nitrogen and phosphorus in the pond by wetland sediment is obvious.During the test of the period of concentrated tail water discharge,As the tailwater discharge time increases,The total nitrogen concentration of pond,ditch,constructed wetland inlet and constructed wetland outlet showed an overall increasing trend.Average total nitrogen concentrations mg·L^-1,9.84mg·L^-1,9.56mg·L^-1,5.52mg·L^-1;Compared with pond concentration,Concentrations of total nitrogen（TN）from pond to outlet were significantly different,Average concentration difference4.73 mg·L^-1,The average purification rate of total nitrogen was 42.5%,The average removal rates of ammonia nitrogen（NH₃-N）,nitrate（NO₃^--N）and nitrite nitrogen（NO₂^--N）were 54.4%,52.0%,58.1%,Can meet the emission standards of aquaculture.Average concentration of total phosphorus0.261mg·L^-1,0.251mg·L^-1,0.238mg·L^-1,0.102mg·L^-1,The average purification rate of total phosphorus was 60.1%;average removal rate of orthophosphate(PO₄^3--P)was 45%.Compared with the previous period,For total phosphorus（TP）content,Further increase in the proportion of orthophosphate((PO₄^3--P),More than 50%.During the experiment,Total phosphorus（TP）content of outlet<0.5 mg·L-1;The concentration of orthophosphate(PO₄^3--P)at the outlet was slightly greater than 0.05 mg·L^-1,Compared with the breeding period,The phosphorus nutrient content in tail water discharge period is higher,The purification rate of nutrients has decreased,However,the tailings treated by constructed wetland-pond circulating water culture system also meet the class II standard of freshwater aquaculture tailings discharge.Combined with the above research results,compared with the traditional ponds,the nitrogen and phosphorus concentrations of wastewater treated by constructed wetland-pond circulating water culture system in the early stage of culture can meet the"fishery water quality standard of the people’s Republic of China"（GB11607-89）;Compared with the early stage of culture,the tail water is discharged centrally,the load of constructed wetland system is increased,the content of nitrogen and phosphorus nutrients in the system is increased to varying degrees,and the removal rate of some nitrogen and phosphorus nutrients is reduced by increasing the nitrogen and phosphorus content in the constructed wetland outlet.In this experiment,both in the early stage of aquaculture and in the late stage of tailwater centralized discharge,the constructed wetland-pond circulating water culture system can better solve the problem of aquaculture wastewater.In order to provide a theoretical basis for the effective and stable operation of constructed wetland.