Relationships Between Plantting Reed And Nitrogen Removal Effectiveness In Subsurface Constructed Wetlands

Reed is is a common wetland plant, because ti is easy to survive and ithas well-developed root system.Horizontal subsurface flow constructedwetlands (HSCWs)with and without reed were investigeted with aitificialwastewater(nitrate-dominated and ammonium-dominated wastewater)and tailwater from Sewage Treatment Plant.In order to study nitrogenremoval processes for low contaminated waters on HSCWs, indicatorsincluding nitrogen concentration, intensity of nitrification/denitrification,plants and other environmental factors were analyzed in the HSCWssystem.And Polymerase Chain Reaction-Denaturing Gradient GelElectrophoresis(PCR-DGGE) technique was used to research the effects ofplants and NH3-N on community structure of AOB (ammonia-oxidizingbacteria) in HSCWs. Culture reed with hoagland medium which imitatesnitrate-dominated and ammonium-dominated wastewater. Root exudate ofreed was detected for organic acid by using HPLC. The influence of rootexudate and organic acid on the microorganism of nitrification anddenitrification was analyzed.Treating nitrate-dominated and ammonium-dominated wastewaterusing HSCWs,the results showed that HSCWs could remove nitratenitrogen effectively when the TN concentration was between6~7mg/L,and HRT was2.5d. When the pollutants were NO3-N and NH3-N, the reedsubsurface flow wetland treatment efficiency of TN reached76.3%and81.9%, respectively. Moreover, ammonium content and reeds significantly improved the nitrification intensity and AOB community structure inwetland. When nitrate-dominated and ammonium-dominated wastewaterwere treated by HSCWs, at50days, the nitrification intensity were0.164mg·kg-1·h-1and0.103mg·kg-1·h-1respectively, and at90days, diversityindex of AOB community were2.32and1.75. When raw water wasammonium-dominated wastewater,as for the wetland planted with reeds,at50days, the nitrification intensity increased from0.082mg·kg-1·h-1to0.164mg·kg-1·h-1, and at90days,diversity index of AOB community rosefrom1.97to2.32. All these experimental results demonstrated thepromotion of ammonium content and reed growth on the nitrogen removaleffciency of wetland.Tailwater from Sewage Treatment Plant was treated by HSCWs.Theresults showed that plant reed can improve the removal ability of TN, thereed subsurface flow wetland removal efficiency of TN reached26.36%when the ρ(TN) was between6~7mg/L, and HRT was2.5d. Improvingwaste loading had no impact on TN treatment. When the ρ(NO3-N) was5.5~8mg/L,the main nitrogen-containing pollutants, the reed and controlsubsurface flow wetland removal efficiency of NO3-N reached27.69%and5.46%respectively. Reed was in favor of the remove of NO3-N andimproving waste loading had no impact on NO3-N treatment ability. Whenthe ρ(NH3-N) was about0.1mg/L, the reed and control subsurface flowwetland removal efficiency of NH3-N reached40.50%and42.17%, andwhen on high waste loading, they increased to72.20%and75.15%respectively. Improving waste loading can increase NH3-N treatmentability, and planting reeds had no impact on NH3-N treatment ability.Moreover, reed growth had no obvious influence on the nitrification/denitrification intensity.Oxalic acid was the most important organic acid in the root exudate ofreed,meanwhile there were formic acid、malic acid、citric acid、tartaricacid、 monoprop and succinic acid in the root exudate. Under theexperiment conditions, root exudate of reed can improve the removal of nitrogen and increase the amount of denitrifying bacteria. The root exudateof reed had a positive effect on nitrification intensity, on the contrary, had anegative influence on denitrification intensity.