Uptake And Removal Of Nitrogen And Phosphorus From Eutrophic Water By Coix Lachrymajobi. L And The Influencing Factors

Water eutrophication is a serious environmental problem in the world.The major factors causing water eutrophication include load of nitrogen(N)and phosphors(P). Many researches have proved that using some large plants to remove nitrogen and phosphorus is an effective way to treat,adjust and control the eutrophication. Therefore,Coix Lachrymajobi.L,a kind of plant can be used as both food supplies and Chinese medicine,was selected to study the possibility to purify eutrophicated water,as well as the effects of environment factors such as pH,temperature and dissolved oxygen on its remove abilities of nitrogen and phosphorus from eutrophicated water.The results of this study,could provide scientific bases for controlling the lake eutrophication.The main results obtained can be summarized as follows:1.Obvious differences of the maximum rates of ammonium,nitrate and phosphorus uptake as well as the Km value of absorption between Coix and rice was observed.The maximum rate of ammonium,nitrate and phosphorus uptake by Coix were 0.0298,0.0302,0.0043rnmol·g^-1FW·hr^-1,respectively;the Km value of the nutrient absorption of Coix were 0.2080,0.6599,0,0308mmoi·L^-1.However,the maximum rate of ammonium,nitrate and phosphorus uptake by rice were 0.0266,0.0270,0.0023 mmol·g^-1FW·hr_-1,respectively;the Km value of absorption of rice were0.3391,0.6051,0.0515 mmol·L^-1.It indicated that Coix is more suitable for improve eutrophicated water with more widely range of NH₄⁺ and phosphorus.2.The effectiveness of Coix for purifying eutrophicated water was studied with simulation experiment and field experiment.The result from simulation experiment showed that the remove rate of total nitrogen,ammonium,nitrate,total phosphorus, dissolved phosphorus and COD_Mnby Coix can reach 84.59%,89.46%,82.66%, 66.36%,51.09%,37.54%respectively,and the pH level of the water decreased from 8.25 to 7.51.The result of constructed wetland experiment achieved the accordant result,and the remove rate of nitrogen,phosphorus and COD_crfrom secondary effluent was also ideal. 3.The removal abilities of nitrogen and phosphorus from eutrophicated water by Coix were studied under different pH,temperatures and dissolved oxygen.In one experiment Lachryma-jobi.L were grownunder 10℃,20℃,30℃,respectively,in another set of experiment the plants were treated with different pH of 4,5,6,7,8,and 9,in the last experiment the plants were grown in aerating water and normal water. From the temperature experiment we can see that the removal rates of total nitrogen, ammonium,nitrate and phosphorus were respectively 67.06%,68,74%,65.66%, 57.52%,which were much higher than those treated under 20℃and 10℃.The results from pH effect experiment showed that the removal rate of total nitrogen reached 77,75%and 78.30%and that of total phosphorus reached to 70.02%and 73.52%at pH 4 and 5.And the removal rates of nitrogen and phosphorus at other pH values were lower,Dissolved oxygen was not so efficiency as pH and temperature in affecting removing nitrogen and phosphorus.These results indicate that more efficient removal of N and P by Coix lacryma-job occurred at relative low pH,high temperature,and high dissoived oxygen.Therefore,this plant could be used for phytoremediation of eutrophic water at summer and autumn seasons.