Effect Of Different Submerged Plants On Water Purification And Case Study

With the sustained and rapid development of economy,the pollution of water bodies such as lakes and rivers is becoming more and more serious.Using submerged plants to purify water quality has the advantages of simplicity,high efficiency,low energy consumption,low investment,and good benefits in the control of water pollution.Based on the adaptability of plants to Hunan’s climate and the purification capacity of sewage,three submerged plants were selected as test materials:Ceratophyllum dermersum,Hydrilla verticillata,and Vallisneria natans.Eight experimental systems were set up.System 1,2,or 3 includes only one plant species,Ceratophyllum demersum,Hydrilla verticillata,and Vallisneria natans,respectively.System 4,5,or 6 contains two plant species,Ceratophyllum demersum and Hydrilla verticillata,Ceratophyllum demersum and Vallisneria natans,and Hydrilla verticillate and Vallisneria natans,respectively.System 7 consisted three plant species of Ceratophyllum demersum,Hydrilla verticillate,and Vallisneria natans.System 8 is the control without any plant.The effects of different plant configuration modes on the purification of simulated water were studied.The dominant plant configurations screened were then applied to the Songya Lake demonstration project to monitor the water quality within a year,and analyze the change trend of pollutant concentrations with time.This study aimed to provide a theoretical and technical support for the selection of submerged plant species and the related application of water ecosystem in the improvement of water environment.The main results were as follows:Ⅰ.Comparative analysis of different submerged plant models on simulated water purification(1)The increment of plant height and biomass in the combination model was lower than that in the single model.Vallisneria natans had a competitive growth relationship with both Ceratophyllum demersum and the Hydrilla verticillata.The increment in plant height of Hydrilla verticilla was the largest among different plant systems.(2)The removal rate of CODcr,TN,TP,and NH3-N in seven plant systems was significantly higher than the control(p<0.05),which ranged from 22.76%～46.54%,21.58～80.08%,73.46～84.33%,and 87.61%～91.97%,respectively.DO concentration maintained 11 mg/L,and Chla concentration was less than 10 mg/m3,indicating that submerged plants could effectively inhibit algae growth and had good water purification capacity.(3)There was a significantly positive correlation between DO and pH in all systems(p<0.01).The total biomass increment was significantly positive correlated with the removal rate of TP(p<0.01)and positively correlated with the removal rate of TN(p<0.05).(4)By analyzing membership functions of seven indicators,including the removal rate of NH3-N,TN,TP,and CODcr,the inhibition rate of Chla,the growth rate of biomass,and the enhancement rate of DO,the ability of plant systems to purify water quality from strong to weak was:System 5>System 1>System 6>System 3>System 7>System 2>System 4.Ⅱ.Water purification effect of submerged plants on Songya Lake demonstration projectThe three dominant mode systems screened by the simulation experiment:the system 5(Ceratophyllum demersum and Vallisneria natans)、the system 1(Ceratophyllum demersum)、the system 6(Hydrilla verticillate and Vallisneria natans).To study the effect of submerged plants on water purification,the Songya Lake project sited as a demonstration project,which verified the submerged plants in the previous test that have good results in purifying water.(1)At three regions of demonstration project,the concentrations of DO,CODMn,TN,and NH3-N reached the Class III standard of surface water,and TP content could reach the Class IV standard of surface water.The pH ranged from the normal range of 6～9 in autumn and winter,but was higher than 9 in spring and summer.The transparency of the demonstration water body was significantly improved.The Chla content was less than 10 mg/m3,and the comprehensive nutritional value was in the middle nutrient state,ranged from 35.36～44.04.The risk of algal blooms was lower.All the tested indicators could meet the water quality requirements of Songya Lake,indicating that the submerged plant configurations in the three regions had good effects on water purification.(2)The TN and TP were the main pollutants in the demonstration project areas,and TN and TP could be remove to some extent in the three areas.The average removal rate of TN and TP in the area 1 was the highest compared with the area 2 and 3.The Ceratophyllum demersum-Vallisneria natans combination pattern could be first considered inthe treatment of Songya Lake.