Study On The Purification Effect Of Two Aquatic Plants On Nitrogen And Phosphorus In Eutrophic Water

The concentration of nitrogen and phosphorus in water body were main factors leading to water eutrophication. Phytoremediation techniques using aquatic plant to controlling eutrophic water is a cost-effective technology. In this study, growth responseof two submerged plants (Hydrilla verticillata and Elodea canadensis) and the changes of TN、TP in plants and sediment in different eutrophic water, modeled by tap water treated with different concentration of N and P, were investigated. Our results were as follows:1、The growth condition (height, branches, biomass) of E. canadensis and H. verticillata were affected by the concentration of nitrogen and phosphorus in water. Within experimental processing extent, the biomass of two aquatic plants was increased, plant height and branch numbers were increased at the beginning two weeks of experiments and subsequently arrested, the growth indexes of plants in treatment group5were lower than other groups, indicated that low concentrations of water (concentration group1,2,3) were conducive to the growth of E. canadensis and H. verticillata, while high concentration of TN and TP in water (concentration group5) had a certain degree of inhibition to plant growth, but did not achieve their threatening level.2、The results of pH values showed that Elodea canadensis and H. verticillata can causing increase of pH values in water body and maintained in an alkaline condition (8-9.5)., but no noticeable changes of the pH values were observed accompanied by the changes of TN and TP concentration in water body.3、The contents of TN enrichment (TNE) of E. canadensis,were17.19、48.26、17.92、47.21、41.69mg respectively according to different concentration treatment. and the contents of TP enrichment (TPE) were4.29、6.83、5.94、16.46、17.29mg accordingly. The trendency of TN and TP enrichment in H. verticillata were similar to in E. Canadensis. The contents of TNE of H. verticillata were5.92、57.07、52.71、79.35、105.18mg respectively and the contents of TPE were3.52、12.13、10.47、18.64、22.54mg. TN and TP contents of two plants all showed the trend of "increased at the first and then decreased".The changes of nitrogen and phosphorus content in plants was impacted by the status of water eutrophication and plant growth condition.4、The result of nitrogen and phosphorus contents in sediment suggested that sediment also played a role in processing of water purification by absorbing parts of nitrogen and phosphorus in water body. At the end of the experment, the rate of TNE in sediment of E.canadensis achieved101-167%,TPE achieved126-187%respectively while the rate of TNE in sediment of H. verticillata achieved134-196%and TPE even reached higher level of164-266%. The level of content of nitrogen and phosphorus enrichment was related to the difference of concentration between sediment and water body..5、The rate of nitrogen and phosphorus removal by E. canadensis and H. verticillata increased according with the increase of TN and TP concentrations in water. The highest rate of TN removal in E. canadensis and H. verticillata water were up to95.97%、90.52%respectively and the highest removal rate of TP were79.23%、79.38%. The peak of purifying effect was focused on the first30days.The absorption capacity of E. canadensis to TN was only accounted for6.51-25.13%of TN removal in water and TP was9.28-17.87%. while the absorption capacity of H. verticillata to TN in water was accounted for7.4-47.55%and TP was12.57-35.26%. The removal of nutrients was partially through absorption of sediment.