| With the accelerated urbanization process and effective control of point source pollution,urban surface runoff, as the second large pollution source for urban water environment besides domestic sewage and industrial wastewater, has become the major reason for deterioration of water quality. Compared with other urban underlying such as roof and green space, road runoff, as the strongest polluted part of urban runoff with high pollutants concentration, is typical of large pollution load and including toxic and harmful substances,especially urban traffic road with high traffic volume. The main sources of road runoff are vehicle’s traffic loss and atmospheric dry and wet deposition. The pollutants, accumulated in road in sunny days,are discharged with runoff in raindays. Some studies have demonstrated that road runoff is the main sources of toxic pollutants such as heavy metal and PAHs in water.In recent years, road runoff, as a hotspot, has been widely concerned by scholars at home and abroad.The sampling station, which was equiped with self-made volume proportional collecting device, was built at south second ring road in Xi’an city. Road runoff caused by rainfall events were sampled from July 2014 to June 2015. Pollution characteristics, pollution load,settleability of urban road runoff in Xi’an city were studied in the dissertation.Study on pollution characteristics of urban road runoff in Xi’an city showed that:(1) EMC of main runoff pollutants cause by 33 storm events varied greatly and the average EMC of SS, COD, dissolved COD, Pb, dissolved Pb, Zn, dissolved Zn, Cu, dissolved Cu, Cd, dissolved Cd, Ni, dissolved Ni, Cr, dissolved Cr, ∑ PAHs were 1272.12mg/L,493.82mg/L, 48.96mg/L, 86.00ug/L, 0.44ug/L, 447.50ug/L, 17.84ug/L, 109.30ug/L, 8.87ug/L,2.33ug/L, 0.06ug/L, 48.27ug/L, 12.75ug/L, 58.42ug/L, 1.58ug/L, 51624.28ng/L, and the coefficient of variation of SS, COD, Pb, Zn, Cu, Cd, Ni, Cr, ∑PAHs were 0.86, 0.74, 0.73,0.65, 1.43, 0.65, 0.68, 0.73, 0.93, 0.55, 0.89, 0.68, 1.32, 0.61, 0.98, 0.43, respectively, which showed that the EMC in road runoff were influenced by many random factors.(2) The correlation of COD, Pb, Zn, Cu, Cd, Ni and Cr with SS were significant at 0.01 level and the correlation coefficients were 0.890, 0.892, 0.875, 0.925, 0.708, 0.758 and0.620,which showed that particulate matters were carried for COD and heavy metal.(3) The occurrence of COD, Pb, Zn, Cu, Cd, Ni and Cr were mainly granular state. The content of particulate were sorted from big to small: Pb>Cd>Cr>Zn>Cu>Ni.(4) The EMC of SS and COD in road runoff in 2014-2015 were lower than in 2009-2010,and the pollution level had been dropping in Xi’an. But the EMC of Pb and Zn of road runoff in 2014-2015 were higher than in 2009-2010, which showed that although conventional pavement cleaning removed the particles in road runoff, it’s difficult to remove fine particulate matter. So the removal effect to heavy metal which stick to fine particulate matter was’ t obvious. With the increase of traffic volume, increasing of the EMC of Pb and Zn showed that vehicle’s traffic loss contribute absolutely heavy metal in road runoff.(5) With the studies at home and abroad, the pollution level of road runoff in Xi’an is higher, and the EMC of SS, COD, heavy metal were is large. This is related to climate, level of air pollution, and level of urban management.(6) The EMC of pollutants in road runoff were unrelated with rainfall volume, rainfall intensity and rainfall duration. The correlation of COD with antecedent dry period were significant at 0.01 level and the correlation coefficients were 0.608, and the correlation of SS,Zn and Cu and Ni with antecedent dry period were significant at 0.05 level and the correlation coefficients were 0.378, 0.358, 0.372 and 0.608, respectively. It showed that the process of being eroded by rain was random and complex, and was influenced by many factors together.(7) The EMC of PAHs in runoff was 19338.59-83117.83ng/L, the average of EMC was51624.28ng/L. The occurrence of PAHs was mainly granular state. The sources of the granular state PAHs were sorted from big to small: asphalt(40.45%) > diesel(25.8%) >gasoline(33.75%). The EMC of dissolved PAHs was 749.86-1306.73 ng/L. The sources of the dissolved PAHs were: gasoline(50.85%), asphalt(32.33%), diesel(16.81%).(8) Heavy metal in road runoff were mainly from vehicle’s traffic loss(59.59%) and atmospheric dry and wet deposition(21.02%). Pb, Zn, Cu, Cr, Ni of road runoff were from vehicle’s traffic loss, and Cd was from atmospheric dry and wet deposition.Study on pollution loads of urban road runoff in Xi’an city showed that:(1) The pollution load of urban road runoff in Xi’an city was quite different between various storm events. The pollution load of SS, COD, Pb, Zn, Cu, Cd, Ni, Cr were1.25kg/hm~2-577.97kg/hm~2, 0.68kg/hm~2-151.6kg/hm~2, 0.15g/hm~2-23.41g/hm~2,1.50g/hm~2-118.76g/hm~2, 0.23g/hm~2-47.99g/hm~2, 0.012g/hm~2-0.656g/hm~2,0.08g/hm~2-11.31g/hm~2, 0.045g/hm~2-13.11g/hm~2, respectively. The dissolved COD, dissolved Pb, dissolved Zn, dissolved Cu, dissolved Cd, dissolved Ni, dissolved Cr were0.09kg/hm~2-12.87kg/hm~2, 0.001kg/hm~2-0.15kg/hm~2, 0.08kg/hm~2-5.29kg/hm~2, 0.03g/hm~2-3.18g/hm~2, 0.001g/hm~2-0.026g/hm~2, 0.05g/hm~2-1.65g/hm~2, 0.003g/hm~2-1.56g/hm~2,respectively.(2) The annual pollution load of SS, COD, Pb, Zn, Cu, Cd, Ni, Cr were6174.27kg/(hm~2·a), 2396.79kg/(hm~2·a), 0.42kg/(hm~2·a), 2.17kg/(hm~2·a), 0.53kg/(hm~2·a),0.011kg/(hm~2·a), 0.23kg/(hm~2·a), 0.28kg/(hm~2·a), respectively. The dissolved COD, dissolved Pb, dissolved Zn, dissolved Cu, dissolved Cd, dissolved Ni, dissolved Cr were237.64kg/(hm~2·a), 0.0021kg/(hm~2·a), 0.87kg/(hm~2·a), 0.043kg/(hm~2·a), 0.0003kg/(hm~2·a),0.062kg/(hm~2·a), 0.008kg/(hm~2·a),respectively. road runoff pollution in Xi’an was serious.(3) The pollution load of SS and COD in road runoff in 2014-2015 were lower than in2009-2010, But the pollution load of heavy metal of road runoff in 2014-2015 were higher than in 2009-2010, which showed that although conventional pavement cleaning removed the particles in road runoff, it’s difficult to remove fine particulate matter. So the removal effect to heavy metal which stick to fine particulate matter was’ t obvious. But with the increasing of traffic volume, pollution load of heavy metal increase, too.Study on settleability of urban road runoff in Xi’an city showed that:(1) The removal efficiency of SS, COD, Pb, Zn, Cu, Cd, Ni, Cr were 43.5-96.8%,35.8-89.2%, 41.9-87.9%, 32.0-54.5%, 17.1-54.9%, 24.1-52.2%, 17.9-51.9%, 15.8-63.1% of 2hours’ settling.2h mean removal efficiency of SS, COD, Pb, Zn, Cu, Cd, Ni, Cr were 74.6%,68.1%, 61.3%, 45.3%, 32.1%, 40.8%, 36.0%, 38.1%, respectively.(2) The pollutants’ removal efficiency was in inverse proportion to surface load. Thesmaller the surface was, the higher removal efficiency was. The surface load decreased1.25-2.83 times as the required particle settling removal efficiency increased 10%.(3) Most of the particles in runoff were fine particles with the diameter of 9-59μm,which showed that the particulates in road runoff was silt. |
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