Absorption And Accumulation Characteristics Of Cadmium In Wetland Plants And Its Application In Irrigation Water Purification

In order to reduce the cadmium pollution in paddy soil and rice,the way of purifying Cd in irrigation water was studied.The removal of Cd in the water by several aquatic plant,Typha angustifolia,Canna indica L.,Myriophyllum spicatum L.and Hydrilla verticillata,in static and dynamic conditions were studied.The effects of inlet Cd content and HRT on the removal of cadmium in the water were studied by simulated constructed wetland.The actual removal effect of cadmium in irrigation water,distribution and change of heavy metal cadmium in the process system and changes of cadmium removal in water under long-term runoff were studied by constructing the field experiment of‘grit chamber+plant pond+artificial wetland+adsorption pool'combined process system.The main test results are as follows:?1?The static removal rate of cadmium was favorable in several aquatic plants,and the maximum removal efficiency was reached at 8h.The concentration of Cd²⁺in the water after several treatments was lower than that of the national standard GB 5084-1992?5?g/L?and decreased to below 2.5?g/L.In the dynamic experiment,the cadmium content in the simulated wetland test water was significantly reduced to below 3?g/L,HRT and the removal rate and the concentration of effluent in each level were correlated.The simulated effluent concentration of artificial wetland was as follows:HRT12h>HRT24h>HRT36h,the removal rate and effluent concentration is just the opposite,the size of the law HRT36h>HRT24h>HRT12h.The Cd²⁺concentration and HRT of the simulated wetland system can affect the removal efficiency of cadmium in the simulated wetland.The higher the concentration of Cd²⁺in the inlet,the higher the concentration of Cd²⁺in the effluent.In the HRT range,HRT has little effect on the removal of Cd²⁺from simulated wetland system.?2?Cd in irrigation water in the selected study area was severe.According to the standard of irrigation water quality in GB 5084-1992,the irrigation water exceeded the standard at a rate of 82.69%,while the soluble Cd content in water was 56.34%,which was potentially harmful.In the study area,the cadmium concentration in the irrigation water was large and susceptible to environmental impact,up to 19.15?g/L,the lowest was only2.72?g/L.At the same time,the influent flow of agricultural irrigation activities was also large,the maximum instantaneous flow up to 60.48m3/h,the lowest was 5.61 m3/h.The removal rate of cadmium in irrigation water was between 82.88%and 100.00%,and the average removal rate was 94.78%.The removal rate of soluble cadmium in the irrigation water was 87.17%-100.00%,the average removal rate was as high as 94.72%,and the running effect was stable,and the influent concentration was less than the influent,the final effluent was less than 2.00?g/L.The concentration of only 0.49?g/L,can effectively remove the total amount of irrigation water and soluble cadmium.During the period from2015 to 2016,the cadmium content in the experimental irrigation water was almost constant.The efficiency of the removal of cadmium in the irrigated water was the same,and the removal efficiency of the soluble cadmium?Cd?was increased and the effective removal of the water Of heavy metal cadmium.?3?The content of cadmium in the base and plant roots of each treatment unit was decreasing according to the direction of water flow,and the change of stem and leaf part was small.The cadmium had a strong ability to enrich the cadmium in the water,which can limit the migration of cadmium in the wetland system.Most of the cadmium in the pod was fixed in the roots of the plant,strong.The results of simulated artificial wetland test showed that the accumulation of heavy metal Cd in sediments was higher than that in plants,and the simulated wetland had the main effect on cadmium interception in water.The specific mechanism needed further investigation and exploration.Water flocculent precipitation,but the water flow more easily when the water migration,mobility was large.And there was a certain risk of secondary pollution,which was needed to be guard against.