Study On Removal Of Pahs And Heavy Metals In Malodorous River Sediment Using Nymphaea Tetragona Georgi And Nelumbo Nucifera

Many urban rivers are becoming malodorous, which is an important environmental issue that must be solved urgently in many big and medium-sized cities of China. The polluted sediment is the main secondary source affecting and restricting the river water quality. After the external pollutions are effectively controlled, a large number of toxic and hazardous pollutants accumulated in sediment will rerelease into the river in certain conditions, causing the secondary pollution. Sediment pollution restoration is one of the difficult problems for the city malodorous river repairation, also the prominent environmental issue on the global scale.The paper is supported by the national key technology and R&D program-"Research and demonstration about urban malodorous river extraneous sources blocking, engineering restoration and multi-level situ ecological purification"(2009ZX07317--006). According to the problem, the study selected two common landscape and water purification aquatic plants Nymphaea tetragona georgi and Nelumbo nucifera as the research plants, with taking the sediment of an urban malodorous river-Gongye river in shanghai as the target, and then the study carried out experimental research, using the Nymphaea tetragona georgi and Nelumbo nucifera to remove the typical persistent organic pollutant PAHs and heavy metals existing in sediment of Gongye river. The study mainly focuses on removal efficiency of PAHs and heavy metals in malodorous river sediment by the Nymphaea tetragona georgi and Nelumbo nucifera, the content and distribution characteristics of PAHs and heavy metals in Nymphaea tetragona georgi and Nelumbo nucifera, the influence of planting Nymphaea tetragona georgi and Nelumbo nucifera on composition of PAHs, speciation of heavy metals and biological toxicity in sediment, aiming to explore the potential and feasibility of using Nymphaea tetragona georgi and Nelumbo nucifera to restore persistent organic pollutants (POPs) and heavy metals in malodorous river sediment, and offering the experiment and data reference for river sediment phytoremediation. The main conclusions are as follows:(1) Nymphaea tetragona georgi and Nelumbo nucifera both have the removal efficiency of PAHs and heavy metals in sediment. For the removal efficiency of PAHs, Nymphaea tetragona georgi is better than Nelumbo nucifera, after176day’s restoration, the removal efficiency of PAHs by Nymphaea tetragona georg is55.9%, while Nelumbo nucifera is32.4%. For the removal efficiency of heavy metals, Nelumbo nucifera is better than Nymphaea tetragona georgi, Nelumbo nucifera is20.42%, while Nymphaea tetragona georgi is18.23%. Overall, the removal efficiency of PAHs is better than heavy metals by planting these two plants. (2) In leaf, sterm and root of Nymphaea tetragona georgi and Nelumbo nucifera, the PAHs content rang is from574.6(Nymphaea tetragona georgi) to1750.5ng/g(Nelumbo nucifera leaf), The difference of PAHs content in Nelumbo nucifera three tissues show more apparent as Leaf(1750.5ng/g)>Root (1239.9ng/g)>Sterm (612.7ng/g), Compared with it, PAHs content in Nymphaea tetragona georgi tissues show small difference as Root (620.9g/g)> Stem (597.1ng/g)> Leaf (574.6ng/g). Overrall, PAHs contents of different tissues in Nelumbo nucifera are all higer than Nymphaea tetragona georgi, the PAHs accumulayion ability of Nelumbo nucifera is better than Nymphaea tetragona georgi.(3) To the composition of PAHs in sediment, there was no significant change before and after planting Nymphaea tetragona georgi and Nelumbo nucifera,2-4ring PAHs are based. The more the2-4rings PAHs contented in sediment, the more benefit for the plants absorb and degrade the PAHs. The percentage of2-4ring PAHs in sediment planted Nymphaea tetragona georgi is higher15.54%than the sediment planted Nelumbo nucifera so that the Nymphaea tetragona georgi had good degradation effection on2-4ring PAHs, reduced from start percentage99.29%to78.43%. Nelumbo nucifera had good degradation effect on4ring PAHs, reduced from49.68%to37.55%. Excepted the2-3ring PAHs content is as much as4ring in Nymphaea tetragona georgi leaf, in other tissues of this two plants, the2-3ring PAHs content is highest, followed the4ring PAHs and the5ring PAHs. The content rang of2-3ring PAHs is44.57%(Nymphaea tetragona georgi leaf)～57.58%(Nelumbo nucifera leaf), the4ring PAHs is23.03%(Nelumbo nucifera sterm)～42.93%(Nymphaea tetragona georgi leaf), the5ring PAHs is8.75%(Nelumbo nucifera leaf)～21.08%(Nymphaea tetragona georgi sterm).(4) Both Nymphaea tetragona georgi and Nelumbo nucifera had a certain ability to accumulate heavy metal and show the same accumulation trend for the five heavy metals as Cu> Ni> Cr> Pb> Cd. The absorption and accumulation amount and type of heavy metals vary differently in two different plants, and the distribution of heavy metals in different tissues of two plants also has difference. The distribution characteristics of Cu and Ni in Nymphaea tetragona georgi is root> leaf> stem, Cd and Pb is root> stem> leaf, Cr is leaf> stem> root. Distribution characteristics of Cr, Ni in Nelumbo nucifera is stem> leaf> root, Cu is stem> root> leaf, Cd and Pb are harmful elements in plants, mainly accumulated in the Nelumbo nucifera leaf. Overall, the accumulation and enrichment ability for the five heavy metals by Nelumbo nucifera is better than the Nymphaea tetragona georgi.(5) The different heavy metal speciation content presented the decreasing trend with the decrease of each heavy metal, and the percentage of various forms of heavy metals in sediment had not changed obviously before and after planting plants. The metal forms of Cd, Cu are increased, and Cr, Pb, Ni mainly existed as residual, and Cd, Cu mainly exist as extractable speciation.(6) Before planting Nymphaea tetragona georgi and Nelumbo nucifera, the biotoxicity of sidement is moderate toxicity, after restorted by Nymphaea tetragona georgi, the biotoxicity of sediment reduced to slight toxicity, after planting the Nelumbo nucifera, the biotoxicity of sediment reduced to non-toxic, compared with the Nymphaea tetragona georgi, Nelumbo nucifera has stronger restoration ability on biotoxicity of the sediment.