Characteristics Of Nitrogen In Urban Runoff And Research On Eco-purifying Box

With the accelerated urbanization in recent years, deterioration of urban water quality was especially significant. Non-point source pollution become particularly significant afterpoint source pollution was mostly under control. Non-point source pollution, such as urban non-point source pollution, agricultural non-point source pollution and the pollution from atmospheric deposition, were more difficult to control than point source pollution. Urban storm runoff has become a major cause of degradation of urban water quality.This paper was supported by the projects of "Major Science and Technology Program for Water Pollution Control and Treatment"(Grant No.2009ZX07317-006), National Natural Science Foundation (Grant No.40971259) and the project of Excellent Academic Leaders of Shanghai (Grant No.10XD1401600). The purpose of this study was to investigate the characteristics of dissolved nitrogen in storm runoff and the first flush effect in urban areas, also to investigate the effect of characteristics of rain and different types of land use on nitrogen pollution. Six land use locations in two watersheds in the city of Wenzhou were selected for sampling during eight storm events. Quality parameters such as dissolved total nitrogen (TDN), ammonium (NH4+), nitrate (NO3-), nitrite (NO2-) of storm runoff water were analyzed. In order to combine water purification technology and riverbank revetment project, a new structure plan was put forward and it was called eco-purifying box. This kind box can be put below the sewer outlet. In different seasons, the purifying effect on artificial rainfall runoff of eco-purifying box was monitored under conditions of different hydraulic retention time.The main conclusions can be summed up as follows.1. The event mean concentrations (EMCs) of TDN, NH4+, NO3-and NO2-varied from0.75to11.84mg N·L-1, from0.40to5.55mg N·L-1, from0.01to4.70mg N·L-1and from0to0.87mg N·L-1, respectively. The EMCs levels of TDN and NH4+were higher than the fifth grade value of national surface water quality standards and lower than second grade value of discharged wastewater quality standards. There were heavy nitrogen pollution at urban traffic road and residential lot. The concentration of nitrogen in urban runoff was affected by characteristics of land use and rainfall characteristics including precipitation, average rainfall intensity, rainfall duration and dry period before the rain.2. The curve of runoff was different from curve of rainfall. When there was a heavy rain, concentrations of TDN and NH4+both decreased during the rainfall. If there was a drizzle, concentrations of NO3-and NO2-in samples from some places increased gradually.3. NH4+dominated dissolved nitrogen in runoffs from traffic road and road in residential lot in both research areas. NH4+still dominated dissolved nitrogen in runoffs from parking lot and roof in residential lot in JS research area, while dissolved organic nitrogen (DON) was the main speciesof dissolved nitrogen in parking lot and NO3-dominated dissolved nitrogen in roof of residential lot in SX research area. If there was interval of runoff, NO3-ratio would increase because of nitrification and ammonification.4. First flush effects of urban runoff wereanalyzed using dimensionless cumulative curve which was defined by Geiger. The first flush effect of NH4+appeared to occur in some runoffs, and the first flush effect of NH4+appeared more frequently, while the first flush effect of NO3-just appeared once or two. If there was obvious first flush effect of nitrogen, the FF30value exceeded40%. The FF30values of TDN, NH4+and NO3-were in the order of NH4+>TDN> NO3-. First flush intensity of NH4+was related to precipitation, runoff amount, average rain intensity and max rain intensity, and first flush intensity of TDN and NO3-were both related to dry period before the rain.5. The phosphorus adsorption characteristics of two substrates (regular ceramsite and biological shale ceramsite) were studied. The results showed that the behaviors of phosphorus adsorption onsubstrates can well be fitted usingboth Langmuir and Freundlish isothermal adsorption equations, and the discriminant coefficient (R2) were above0.90. The phosphorus adsorption capacity of regular ceramsite and biological shale ceramsite were123mg kg-1and147mg kg-1. Regular ceramsite had a better phosphorus adsorption capacity than biological shale ceramsite, so regular ceramsite was selected tobe used in the eco-purifying box.6. In order to combine water purification technology and riverbank revetment project, eco-purifying box was put forward. Experiment results showed that the box had good purifying effect on artificial runoff in summer. It could remove more pollutants from water with increasing hydraulic retention time. The eco-purifying box can remove NH4+,NO3-, PO43-and CODCr with the efficiency of2.07-2.61g N·m-2·d-,0.13～2.18g N·m-2·d-1,3.37～5.99g P·m-2·d-1and60.05～93.24g·m-2·d-1, respectively.