| In recent years,with the rapid development of industrial production and the intensification of human activities,the environmental problems caused by PAHs pollution of water bodies have become increasingly prominent,Many rivers and lakes in China are polluted by PAHs in varying degrees.Many PAHs are toxic,mutagenic and carcinogenic.Increased concentration of PAHs in water will do great harm to animals,plants and ecosystems,and accumulate in plants and animals,thus endangering human health.Constructed wetland is a new sewage treatment technology proposed in the 1970 s.It is an ecosystem designed,constructed and regulated by human beings.It is mainly composed of plants,substrates,microorganisms and sewage water,the purification of sewage is mainly achieved through the synergistic action of chemistry,biology and physics.The PAHs removal pathways in constructed wetland system mainly include matrix adsorption,plant absorption and microbial degradation.However,there are few studies on PAHs removal by constructed wetland system in China.Based on field investigation of typical constructed wetlands in Shandong Province,the wetland of Zhu Long river was selected as the research object,the distribution characteristics of naphthalene and phenanthrene in the constructed wetland system were analyzed.Artificial water distribution was used to simulate the inflent of the Zhu Long river wetland.A vertical subsurface flow constructed wetland was constructed in the laboratory.The purification effect of different plants on PAHs polluted water and the physiological responses of plants under different concentrations of PAHs stress were studied,The main research results are as follows:(1)The results showed that the removal rates of naphthalene and phenanthrene were41.84% and 70.36% respectively in the constructed wetland system,The naphthalene and phenanthrene contents in the V water of the Zhu Long River were reduced after the ecological treatment.The contents of naphthalene and phenanthrene in four wetland plants,Irispseudacorus L,Scirpus validus Vahl,Phragmites australis and Zizania latifolia,were determined.The results showed that the enrichment effects of naphthalene and phenanthrene in different plants were different.The order from high to low was Iris pseudacorus L,Scirpus validus Vahl,Phragmites australis and Zizania latifolia.The determination results of naphthalene and phenanthrene in subsurface wetland filler and surface wetland sediment show that the adsorption effect of subsurface wetland filler on naphthalene and phenanthrene is better than that of surface wetland.(2)The simulated constructed wetland system had a good removal effect on conventional pollutants.The average removal rate of COD from four wetland plants Phragmites australis(58.29%)> Scirpus validus Vahl(48.57%)> Thalia dealbata Fraser(44.43%)>Iris pseudacorus L(43.57%).The average removal rate of TN from four wetland plants Scirpus validus Vahl(74.70%)> Iris pseudacorus L(70.22%)> Phragmites australis(69.39%)>Thalia dealbata Fraser(68.69%).The average removal rate of TP from four wetland plants Phragmites australis(93.85%)> Iris pseudacorus L(92.28%)> Scirpus validus Vahl(89.05%)> Thalia dealbata Fraser(81.57%).(3)The simulation results showed that different wetland plants had different removal effects on naphthalene and phenanthrene,the removal rates of naphthalene and phenanthrene were all over 55% and 40% respectively,The average removal rate of naphthalene by plants was Phragmites australis(75.60%)> Iris pseudacorus L(59.56%)> Thalia dealbata Fraser(59.01%)>Scirpus validus Vahl(55.42%).The average removal rate of phenanthrene by plants was Iris pseudacorus L(66.08%)> Phragmites australis(55.17%)> Thalia dealbata Fraser(55.06%)> Scirpus validus Vahl(41.14%).(4)With the increasing concentration of naphthalene and phenanthrene in simulated wetland system,the removal rates of naphthalene and phenanthrene by Phragmites australis and calamus decreased gradually.When the influent concentration of naphthalene was 50ng/L,the removal rates of naphthalene by reed and Iris pseudacorus L were the highest,the removal rates of naphthalene by Phragmites australis and Iris pseudacorus L were the lowest at800ng/L,78.59% and 73.41% respectively,The removal rates of phenanthrene by Phragmites australis and Iris pseudacorus L were 69.40% and 58.64% respectively.When the influent concentration of phenanthrene was 20 ng/L,Phenanthrene removal rate of Phragmites australisand Iris pseudacorus L was the highest,78.45% and 73.36% respectively.When the influent concentration was 400 ng/L,Phenanthrene removal rate of Phragmites australis and Iris pseudacorus L was the lowest,58.06% and 62.46% respectively.(5)Different concentrations of naphthalene stress induced the physiological characteristics of Phragmites australis.With the increase of naphthalene concentration,the chlorophyll content of Phragmites australis leaves decreased,resulting in the withered and yellow leaves of Phragmites australis.With the increase of MDA content,the activities of SOD and POD increased,the activities of CAT first increased and then decreased,and the growth and life activities of reed were obviously inhibited.The removal efficiency of naphthalene by reed might be affected.(6)Different concentrations of phenanthrene stress induced changes in physiological characteristics of Iris pseudacorus L.With the increase of phenanthrene concentration,the chlorophyll content of Iris pseudacorus L leaves decreased,resulting in the yellow of Iris pseudacorus L leaves.MDA content increased,SOD activity increased,CAT and POD activity increased first and then decreased,but the overall trend was upward.The growth and life activities of Iris pseudacorus L were significantly inhibited,and the removal efficiency of phenanthrene by Iris pseudacorus L might be affected. |
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