Study On Decontamination Simulation Experiment Of Vertical Subsurface Flow Constructed Wetland

As an ecological wastewater land treatment technology, constructed wetland hasmany advantages such as good efficiency of nitrogen and phosphorus removal, lowoperation cost, easy to operate and manage, wide applicability and significantenvironmental benefits. But its removal effect of pollutants can be affected bymany factors. To seek optimal wetland pattern so as to improve the pollutantsremoval efficiency, this study investigates the influence of matrix type, substrateand hydraulic retention time on the removal efficiency and based on this atwo-stage constructed wetland is designed in the Linhai Mining subsidence area inHuaibei.First, this study takes ceramisite, volcanic, gravel, medical stone and steel slagas the research objects. Static experiment is carried out based on the analysis of thematrix composition and the phosphorus isothermal adsorption curves of them aredraw out. Then their saturated adsorptions are compared and the effects oftemperature and PH on adsorption characteristics are analyzed. The results showthat the absorbing ability of P is in the ascending order of steel slag＞ceramisite＞volcanic＞medical stone＞gravel. As the matrix will go off when the adsorption issaturated, in this study they are regenerated with alternate drying-wettingtreatments to prolong their life. The results show that the removal efficiency ofeach matrix all recover to a certain level except the gravel. Matrix regeneration canbe realized through intermittent operation.Second, dynamic experiment is carried out to simulate vertical subsurface flowconstructed wetland. As the matrixs in wetland system, influence of steel slag andceramisite and their mixture on pollutants removal efficiency under differenthydraulic retention time with different operation condition are compared. Theexperiment is also improved by intermittent aeration inside the matrix. The resultsshow that the removal efficiency of NH₄⁺-N, TN and TP is in the ascending order ofsteel slag, steel slag and ceramisite（1：1）, steel slag and ceramisite（1：2）,ceramisite, while that of NO₃—N, NO₂—N and TOC is in the ascending order ofceramisite, steel slag and ceramisite（1：2）, steel slag and ceramisite（1：1）, steelslag. Taking both purification ability and acid buffering capacity into consideration comprehensively, the mixture of steel slag and ceramisite is the more idealsubstrate of wetland. When the HRT was2h, pollutant removal efficiency of eachsystem is higher than when it is1h. After the intermittent aeration, removalefficiency of NH₄⁺-N, TN and TP of steel slag and ceramisite（1：2）as well as slagand ceramisite（1：2）are all significantly increased, while that of NO₃—N, NO₂—Nall slightly decreased.Finally, vertical subsurface flow constructed wetland is designed according tothe site situation. As for this design, water quantity objective is to meet therequirement of80,000m3/d, while water quality target is expected to maintain thewater quality of the subsidence lake at class III-IV in order to meet the demand forindustrial water, and landscape target is to create landscape richness and speciesrichness. The wetland design selects a combined process, vertical subsurface flowconstructed wetland as the first stage while horizontal one as the second stage.