A Study Of The Intensification Strategies For Constructed Wetlands And The Effectiveness Evaluation

Constructed wetlands(CWs)have been widely applied for the treatment of waste water.However,the removal efficiency of nitrogen and phosphorus in CWs was limited and unsteady during operation in the practical use(e.g.when temperature was decreased),which restricted the large-scale application of CWs in C hina.Therefore,it is very important to improve the removal efficiency of pollutants(e.g.,nitrogen and phosphorus)in CWs.In this study,the CWs with different strengthening measures were established.The results showed that intermittent aeration(12 h/d),addition of cornstalk,the application of ferric-carbon micro-electrolysis material(FCME)as substrate,and the application of up-flow(UF)could improve the performance of CWs,especially,under varying temperature falls.The result could offer a technological support for the treatment of waste water in C hina,especially,under varying temperature falls.The major findings of this study were as follows:(1)It was found that the intermittent aeration 12 h/d substantially improved the removal percentages of ammonia nitrogen(AN),total nitrogen(NN)and chemical oxygen demand(COD).The removal percentages of AN,NN and COD were 93.9%,95.4% and 92.8%,respectively.It was about 11.0%,12.2% and 20.7% greater than the CWs without intermittent aeration(NA).During the experiment of different C/N ratios,the removal percentages of AN were relatively stable and ranged from 98.4-100%.However,the removal percentages of COD were decreased with the increasing of C/N ratios.The result demostrated that intermittent aeration12 h/d was suited to the treatement of the waste water with the C/N ranged from 3.1-9.2.During the experiment of temperature influence,the removal percentages of AN and COD were relatively stable.The removal percentages of AN were greater than 97.7% and the removal percentages of COD were ranged from 80.7-98.0%.Nevertheless,the removal percentages of AN and COD were substantially influenced by the declined temperature in CWs without aeration.The removal percentages of AN decreased by 2.9-11.2% and the removal percentages of COD were ranged from 43.4-75.2%.Overall,the intermittent aeration(12 h/d)could improve the performance of CWs even at a low temperature.(2)Sustained-released carbon-source(SRCS)added into CWs can improve the performance of CWs.During the experiment with different influent concentrations of total nitrogen(TN),the removal percentages of AN and TP were greater than 87.4% and 91%,respectively.However,the removal of NN was substantially decreased when the influent concentration of TN reached 179.5 mg/L.For example,the removal percentages of TN were 86.8,84.7 and 76.2%,respectively,in the CWs with corncob,wood and control.While,the removal percentages in CWs with cornstalk was still greater than 92.1%.During the experiment of temperature influence,the removal percentages of AN and TN were decreased with the decline of temperature in CWs with SRCS.However,the CWs with SRCS(Sustained-released carbon-source)can still show good performance during the operation.In the CWs with cornstalk,the removal percentages of AN,NN and TN was still greater than 89.7%?81.0% and 82.8%,respectively,even if the influent concentrations of TN was increased to 179.2 mg/L and under low temperature.O verall,CWs with cornstalkcould acclerate the rate of denitrification reaction and increase the removal percentages of NN under low temperature.(3)CWs incorporated with FCME as substrate showed a good adsorption capacity of TP.When the influent concentration of TP was up to 32.8 mg/L,the removal percentage of TP was still greater than 96.6%.Meanwhile,the CWs also showed high removal percentages of AN,NN,TN and COD.During the expriment of temperture influence,the removal percentages of AN,NN,TN and COD were greater than 82.8%?81.9%?85.8 and 80.3%,respectively even at the low temperature.However,the removal percentages of AN,NN and TN were unsteady.During the expriment of different influent concentrations of COD,the removal percentages of COD were greater than 83.8%,and CWs incorporated with FCME also showed high removal percentages of AN(92.9%),NN(94.1%),TN(95.2%)and TP(95.3%).During the expriment of different influent concentration of NN,the removal percentages of NN were still greater than 92.4% even when the influent concentration of NN was up to 75.8 mg/L.O verall,FCME was a potential substrate to enhance the performance of CWs.It was suited to the treatment of the waste water co ntaining high concentration of TP,COD or NN.(4)The CWs with up-flow(UF)generally showed a better performace as compared to other flow modes.The UF-CWs showed a better performance with the removal percentages of AN(99.7%),NN(87.2%),TN(93.1%),TP(95.4%)and COD(87.7%),respectively.The result also indicated that the performance of CWs with different flow was influenced by the change of temperature.However,the SSL-CWs was less affected by the temperature as compared to other CWs.The removal percentages of AN,NN,TN,TP and COD were greater than 94.8%?67.6%?78.4%?98.5% and 77.9%,respectively.Overall,the results of this study demonstrated that the strengthen measures of intermittent aeration(12h/d),the addition of SRCS in CWs(especially with cornstalk),the application of FCME and the up-flow(UF)water mode could enchance the performance of CWs and still show good performance even at low temperature.Additionally,the result can also offer a suggestion for choose appropriate reinforcement measure according to the property of waste water.