Purification Efficiency Of Four Types Of Wetland Plants On Eutrophic Water Body

Excessive fertilization,increased resident polluted water and unqualified industrial wastewater polluted surface water.Constructed wetlands has been widely used because of their stronger purifying capacity,lower cost,easier to build,less operation and maintenance requirements.The design of constructed wetlands is very important in pollution control,therefore,it is necessary to study the contribution of substrate,wetland plant and microorganism in the process of removal of pollutants.Four wetland plant species(Acorns calamus,Typha orientalis,Lemna minor,Ceratophyllum demersum)were grown to compare the purification efficiency of wetland plant species alone and in combination on two eutrophic water bodies,high nutrient wastewater(influent)and low nutrient wastewater(effluent)in a wastewater treatment plant.This paper studied the contribution of substrate,wetland plant and microorganism in the process of removal of pollutants.The main research conclusions are as follows:(1)The concentration of total nitrogen(TN),total phosphorus(TP)and chemical oxygen demand(COD)decreased sharply at the beginning of the test(June and July),but this decreasing trend slowed down in the late phase(from August to October).The wetland plants could remove TN,TP and COD from wastewater effectively,but the degree of purification is different between different wetland plant species and between different combinations of these species.In the high nutrient treatment,the TN removal rate were 82.15%～94.79%,and in the low nutrient treatment,the ranges of TN removal rate were 74.54%～94.65%.In the high nutrient treatment,the NH4+-N removal rate were 82.28%～95.71%,and in the low nutrient treatment,the ranges of NH4+-N removal rate were 71.30%～93.58%.In the high nutrient treatment,the NO3--N removal rate were 61.19%～76.00%,and in the low nutrient treatment,the ranges of N03--N removal rate were 46.43%～70.86%.The wetland plant species were more effective in reducing TN,NH4+-N and NO3--N when used in combination than used alone,and the combination of Typha orientalis,Lemna minor and Ceratophyllum demersum had the highest efficiency.In the high nutrient treatment,Typha orientalis was more effective in reducing TP and PO43-,and the combination of Typha orientalis,Lemna minor and Ceratophyllum demersum had the higher efficiency in removing TP and P043-in the low nutrient treatment.In the high nutrient treatment,the COD removal rate were 85.1%-96.0%,and Acorus calamus and Typha orientalis had the highest efficiency;in the low nutrient treatment,the COD removal rate were 76.9%～94.8%,and the combination of Acorus calamus,Lemna minor and Ceratophyllum demersum had the highest efficiency.The pH was improved in both of these two treatments.(2)In the high nutrient treatment,the TN content in the substrate of Lemna minor and Ceratophyllum demersum treatments was higher at the end of the test than at the beginning of the test.However,the TN content in the substrate of Acorus calamus,the combination of Typha orientalis,Lemna minor and Ceratophyllum demersum,Typha orientalis,the combination of Acorus calamus,Lemna minor and Ceratophyllum demersum was lower at the end of the test than at the beginning of the test.In the low nutrient treatment,the TN content in the substrate of wetland plant treatments was lower at the end of the test than before.In both of the water,the TP content and organism content were higher the end of the test than before.(3)The wetland plants’ absorption and microbes’ decomposition are the main ways in removing N.The substrate’ absorption is the main way in removing P.The wetland plants’ absorption and microbes’decomposition are the main ways in removing organism.