| Severe drought has hit Southwest China from the autumn of2009to the spring of2010. Southwest drought is a typical extreme weather event under the influence of global climate change. To probe into the pollution characteristics of urban rainfall runoff after persistent meteorological drought, the characteristics of Kunming urban runoff pollution has been studied, and the impact of the runoff pollution on river water quality has been analyzed. An experimental system of combined oxidation pond and constructed wetland was built by selecting suitable substrate and wetland plants, which was then used to deal with heavily polluted river water by rainfall runoff after the severe drought. When stored river water had been treated, the system must continue to run in order to be maintained. During maintenance operation, the efficiencies of the experimental system to treat high polluted river water in rain spell under "pond for water regulation and retardation-recirculating treating" operating conditions and low polluted river water in dry spell under "continuous inflow-continuous outflow" operating conditions has been studied. Finally, the pilot-scale system of combined oxidation pond and horizontal subsurface flow constructed wetland has been designed according to local conditions and used to treat urban polluted river water. The major results are showed as follows:(1) The concentrations of pollutants in the three processes of rainfall runoff after the once-in-a-century drought decreased with the increasing of flow time as a whole. Urban surface runoff possessed less biodegradability, so that it was not suitable to adopt common biological treatment of wastewater to purify it. TP, COD and heavy metal mainly existed in particulate-bounded insoluble phase, but Both TN and BOD5mainly existed in dissolved phase. The heavy metals obviously had a common origin. The three rains all led to obvious first flush effect with regard to TN, TP, COD, BOD5, SS, Cu, Zn, Cd, Pb, Fe, Mn and Cr. Urban runoff pollution in Kunming after the severe drought was serious compared to other cities concerned and Kunming in normal climate.(2) The overflow runoff after the severe drought heavily polluted the river. Compared with the quality of river water in normal rainy season, deterioration rate of river water quality caused by pollution of the first three rainfall runoffs after the severe drought was between18%to75%; compared with normal dry season, deterioration rate even reached up to52%～273%.(3) Wetland plant selection experiment showed that Cannaceae indica var. flava and Cyperus slternifolius which are green all the year around grew best and showed the best integrated purifying performance compared to the other five species of macrophyte, so they were the most suitable macrophyte planted in wetlands. The adsorption capacity of pumice to NH4+-N and P was distinctly higher than lightweight ceramic pellet and haydite. However, the rate of saturated pumice NH4+-N and P desorption was lower than the other two substrates. Therefore, pumice was a better constructed wetland substrate to remove NH4+-N and P from wastewater.(4) The combined system of aerated pond and subsurface constructed wetland using pumice as substrate could treat the heavily polluted river water efficiently. The mean removal rates of SS, COD, TP and NH4+-N were over90%, and TN was60%. The treated water met the standard A of grade I discharge standard of pollutants for municipal waste water treatment plant (GB18918-2002).(5) In the period of maintenance operation, the combined system of oxidation pond and subsurface constructed wetland with two different operating behaviors could treat urban slightly polluted river water in dry spell of both warm and cold season and urban heavily polluted river water in rain spell efficiently. The removal rates of SS, COD, TP, TN and NH4+-N from low polluted river water in dry spell were over86%,56%,85%,42%and67%respectively, and those from high polluted river water in rain spell were98%,87%,94%,53%,88%respectively. The treated water by the system with two different operating behaviors met the standard A of grade I discharge standard.(6) The pilot-scale system of combined oxidation pond and constructed wetland with intermittent inflow and continuous outflow could treat urban slightly polluted river water in dry spell of both warm and cold season and urban heavily polluted river water in rain spell efficiently. The removal rates of SS, COD, TP, TN and NH4+-N from low polluted river water in dry spell were over88%,58%,69%,35%and53%respectively, and those from high polluted river water in rain spell were93%,73%,80%,61%,81%respectively. The treated water met the standard A of grade I discharge standard. |
PDF Full Text Request