Study On The Restoration Of Urban Polluted Water And Sediment Using The Combined Iron-carbon Carriers And Floating Green Island

With the rapid development of China's industry and the acceleration of urbanization,a large number of nitrogen,phosphorus and other pollutants are discharged into urban water bodies without effective treatment,resulting in black and odorous problems,as well as eutrophication.Therefore,it is of great significance to control the pollution of nitrogen,phosphorus and other pollutants and carry out the effective restoration of polluted water bodies and sediments in urban regions.At present,the commonly used in-situ repair technologies have limited repair ability and need long repair time.The development of iron-carbon carriers coupled floating green island technology in our laboratory provides a new idea for solving the problem of polluted water bodies and sediments in urban regions.The target of this study is to repair polluted water bodies and sediments intensely and quickly.This study analyzed the repair effect by using the iron-carbon carriers,and then carried out a comparative experiment between the iron-carbon carriers and conventional chemical oxidants.Furthermore,the iron-carbon carriers coupling floating green island restoration system was established and analyzed in a lab-scale experiment,in the aspect of pollutant removal efficiency,microbial population structure and degradation dynamics.Finally,a pilot-scale experiment was further established to explore it's practical application in the field of urban water treatment.The main results are as follows.(1)Density experiment and oxidant comparison were carried out for the restoration effects of the iron-carbon carriers on polluted water bodies and sediments,and the results showed that:?The removal efficiencies of 81.9%,100%,97%and 65.9%were achieved for NH4+-N,NO3--N,TP and chl-a by using iron-carbon carriers in water restoration.In the sediment remediation,the removal efficiencies of NH4^-N,TN,TP and COD reached to 97.1%,74.6%,94.4%and 97.8%,respectively.The restored water transparency changed from opaque to clear bottom,and from odor to tasteless.(2)A study was carried out on the laying density of sediments in polluted water with iron-carbon carriers of 40 cm3·L-1 and 80 cm3·L-1.The results showed that the 80 cm3·L-1 treatment group had significantly improved the removal effects of pollutants,compared with the 40 cm3·L-1 treatment group.Therefore,the density of 80 cm3·L-1 was chosen for the follow-up study.(3)In the comparative experiment with oxidants,the iron-carbon carriers,H2O2,Ca(NO3)2,Ca(C10)2 and superposed oxidants were used.The results showed that the electrochemical action of iron-carbon carriers enhanced the removal efficiencies of pollutants,and it had the advantage of no secondary pollution.In particular,the removal of NH4+-N and TP by the iron-carbon carriers was superior to the other oxidants.(2)The iron-carbon carriers combined floating green island restoration system was established to repair a kind of black and odorous sediment in a lab-scale experiment,together with the addition of H2O2 and Ca(NO3)2.The results showed that the coupling system reached the removal efficiencies of 72.9%,85.1%and 96.4%for NH4+-N,TN,TP,and TOC,respectively,which were much higher than those in the control group(32.6%,0.5%and 38.8%).High-throughput sequencing results indicated that the dominant bacteria in the system included unclassified_Anaerolineaceae,Thiobacillus,unclassified_Chloroflex and unclassified Xanthomonadales.The typical autotrophic denitrifying bacteria in the coupling system(such as Thiobacillus)could enhance its ability to remove nitrogen.(3)In the pilot-scale experiment,the iron-carbon carriers coupling floating green island restoration system was applied to the Yanjing Lake and Yueya Lake in Xiangshan park.After 50 days restoration,the removal efficiencies of 42.5%,98.5%and 82.1%for Yanjing Lake and 67.5%,42.8%and 72.3%for Yueya Lake were achieved for NH4+-N,TP and chl-a.The results of water quality assessment indicated that Yanjing lake was repaired from "moderate eutrophication" to "poor nutrition",and Yueya lake was repaired from "eutrophication" to "medium nutrition".The economic analysis indicated that the cost of iron-carbon carriers are 2.45 yuan/kg,and the investment cost in the pilot-scale experiment is 5.04 yuan/m3 a year,which showed a feasible investment cost in some extent.In summary,the application of iron-carbon carriers coupling floating green island restoration system can improve the repair effects of urban polluted water bodies and sediments,indicating that it has a good prospect in practical engineering application.52 sets of figures,18 tables and 86 references were included in this paper.