| Microplastics is an emerging contaminants that has attracted widespread attention in recent years,and it is prevalent in Marine and inland river environments.Constructed wetland is considered to be a better choice for advanced sewage treatment and river water quality improvement because of its reliable removal effect,simple management and low cost.Studying the removal efficiency and influencing factors of different types of constructed wetlands on microplastics in water will help promote the application and promotion of constructed wetland treatment technology in the field of microplastics control in water environment.In order to study the effect of multi-media horizontal subsurface constructed wetlands on microplastics in water bodies,this study took the horizontal subsurface wetland units that grow iris,celandine,and canna plants as the research object.The content and size of microplastics were compared,and the removal effects of different plants on microplastics in water were compared,and the removal rules of wetlands for microplastics of different sizes were explored.By investigating the content of microplastics near the roots of different plants,the differences in the removal of microplastics from different parts of plants were compared,and the mechanism of removing microplastics from plant roots was analyzed and summarized.By investigating the content and size characteristics of microplastics in the influent and effluent of the constructed laboratory model,the efficiency of removing microplastics from constructed wetlands under unplanted conditions was explored.By investigating the microplastic content and size distribution characteristics of different particle size layers and different parts of the same particle size layer in the wetland model,the removal effects of different particle size matrices and different parts of the same particle size layer on microplastics were analyzed and compared.Combined with physical wetland research and laboratory model research,the removal mechanism of horizontal subsurface constructed wetlands for microplastics was reasoned and analyzed.The main findings are as follows:(1)all the multilayered medium level,the undercurrent of artificial wetland unit for the micro plastic water has obvious removal effect,but the removal efficiency by the influence of various conditions are prone to volatility,and compared with sewage treatment plant for the micro plastic removal efficiency,such as more than medium level,the undercurrent of artificial wetland removal efficiency is relatively low.Combined with other sewage treatment technologies,constructed wetlands can help to achieve water purification goals and control microplastic content in water.(2)The removal effects of IRIS yellow,Lythymus gigas and Canna wetland unit on microplastics in water was in the order of Lythymus gigas wetland unit > Canna wetland unit > Iris yellow wetland unit.In two weeks,64.29% of the iris yellow wetland unit showed a removal effect of more than 20%.The removal rate of 92.86% of the unit removal effects was above 20%.The removal rate of canna wetland unit was above 20% in 85.71%.The removal effect of rhizomatous iris yellow was obviously weaker than that of fibrous rhizomatous lythrum and canna.(3)The microplastics content in the effluent of the three plant wetlands with the size of less than 400μm increased to a certain extent,and the removal rate of microplastics in the size of 400-800 μm was 20-50%,while the removal rate of microplastics in the size of more than 800μm was above 50%.The content of microplastics below 400μm in the effluent of wetland model increased,and the size removal rate of microplastics above 400μm was above 50%.The removal efficiency of microplastics is inversely proportional to size.The horizontal and vertical flow of water between different particle size layers leads to continuous collision and friction between microplastics in water and coarse filler,which accelerates the decomposition of larger microplastics into smaller microplastics,and leads to the increase of the content of small and medium-sized microplastics in the water.(4)The content of microplastics in plant roots of IRIS yellow,Lythylidus and Canna wetland units decreased along the direction of horizontal water flow,and microplastics were mainly distributed in the front of wetland units.The size of microplastics near the roots of the three plants is more than 400μm,and the proportion of microplastics smaller than400μm is small.Therefore,plant roots have a better removal effect on the content of microplastics of larger size.(5)The distribution of microplastics content in the wetland model is as follows: 30-50 mm layer > 50-80 mm layer > 100-120 mm layer.Microplastics are mainly adsorbed and settled in the substrate with 30-50 mm particle size,and the removal and interception effect of microplastics in the horizontal subsurface flow wetland unit is inversely proportional to the particle size of the substrate.The distribution pattern of microplastics content in the same medium layer is front > middle > back,indicating that it is easier to trap microplastics in the front area of the same layer wetland unit.Compared with the substrates with 30-50 mm and 100-120 mm particle sizes,the adsorption removal effect of the substrates with50-80 mm particle sizes was more balanced for microplastics of all sizes.(6)The interception of wetland plant roots,the adsorption of matrix biofilms,the sedimentation of suspended solids and the engulfment of some wetland organisms play an important role in the removal of microplastics from water bodies. |
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