Laboratory Study on Stormwater Runoff Treatment via Sand-Based Micron-scale Pore Pervious Paver

Stormwater runoff samples from a road in China were collected and analyzed for pH,TSS(total suspended solid),TDS(total dissolved solid),COD(chemical oxygen demand),TP(total phosphorus),TN(total nitrogen),Pb,Al,Zn,Fe,Cd,and Mn.Results showed that the pollutant concentrations from road runoff were relatively high.TSS and COD concentrations exceeded the Class B effluent requirement of the Chinese Standards of Pollutant Discharge from municipal WWTPs(wastewater treatment plants).COD,TP,and TN concentrations exceeded Class V of the Chinese Environmental Quality Standard for Surface Water.TSS,Zn,Fe,and Al concentrations exceeded the USEPA(U.S.Environmental Protection Agency)benchmark values.All these indicated proper runoff treatment to avoid negative impacts on the environment is needed.Metal partitioning analysis was conducted and it showed that Pb,Al,Zn,Fe,and Mn exist mostly in particulate forms in the runoff.Thus,gravitational settlement and filtration can still be cost-effective methods for removing most of these metals.Runoff samples were treated through two bench-scale laboratory set-ups,composed of micron-scale pore pervious paver systems and subsoil.The average removal rates of TSS,TP,and TN were 95.2%,81.8%,64.1%,and 64.4%,respectively.The removal rates of Pb,Al,Zn,Fe,and Cd also reached 50%-99.2%.The tested sand-based pervious paver has micron-scale pores with good filtration potential.The system can effectively reduce stormwater runoff pollution,thereby reducing the potential for groundwater pollution.In addition,residues and sediments collected from the surfaces of the pervious pavers were also tested.The metallic constituents in the residues and sediments were correlated to these in the runoff.Pb and Cr were low in the residues,but Zn exceeded the Class A limit of the Chinese Control Standard of Pollutants in Sludge for Agricultural Applications.Thus,proper disposal of the solid wastes generated from the pavers is also to be further investigated.

Pollutant concentrations and pollution loads in stormwater runoff from different land uses in Chongqing

To investigate the distribution of pollutant concentrations and pollution loads in stormwater runoff in Chongqing,six typical land use types were selected and studied from August 2009 to September 2011.Statistical analysis on the distribution of pollutant concentrations in all water samples shows that pollutant concentrations fluctuate greatly in rainfall-runoff,and the concentrations of the same pollutant also vary greatly in different rainfall events.In addition,it indicates that the event mean concentrations （EMCs） of total suspended solids （TSS） and chemical oxygen demand （COD） from urban traffic roads （UTR） are significantly higher than those from residential roads （RR）,commercial areas （CA）,concrete roofs （CR）,tile roofs （TRoof）,and campus catchment areas （CCA）;and the EMCs of total phosphorus （TP） and NH3-N from UTR and CA are 2.35-5 and 3 times of the class-III standard values specified in the Environmental Quality Standards for Surface Water （GB 3838-2002）.The EMCs of Fe,Pb and Cd are also much higher than the class-III standard values.The analysis of pollution load producing coefficients （PLPC） reveals that the main pollution source of TSS,COD and TP is UTR.The analysis of correlations between rainfall factors and EMCs/PLPC indicates that rainfall duration is correlated with EMCs/PLPC of TSS for TRoof and TP for UTR,while rainfall intensity is correlated with EMCs/PLPC of TP for both CR and CCA.The results of this study provide a reference for better management of non-point source pollution in urban regions.

Uncertainties in stormwater runoff data collection from a small urban catchment, Southeast China

Monitoring data are often used to identify stormwater runoff characteristics and in stormwater runoff modelling without consideration of their inherent uncertainties. Integrated with discrete sample analysis and error propagation analysis, this study attempted to quantify the uncertainties of discrete chemical oxygen demand （COD）, total suspended solids （TSS） concentration, stormwater flowrate, stormwater event volumes, COD event mean concentration （EMC）, and COD event loads in terms of flow measurement, sample collection, storage and laboratory analysis. The results showed that the uncertainties due to sample collection, storage and laboratory analysis of COD from stormwater runoff are 13.99%, 19.48% and 12.28%. Meanwhile, flow measurement uncertainty was 12.82%, and the sample collection uncertainty of TSS from stormwater runoff was 31.63%. Based on the law of propagation of uncertainties, the uncertainties regarding event flow volume, COD EMC and COD event loads were quantified as 7.03%, 10.26% and 18.47%.

Application of Green Roof in Relieving Urban Waterlogging: A Review

Green roof plays a critical role in regulating roof runoff by reducing runoff, delaying runoff generation, reducing runoff peak flow and improving runoff water quality effectively. On the basis of introducing significance and role of green roof, this paper reviewed domestic and international researches on the green roof's control over roof runoff, and analyzed the factors that influence the control of green roof over the runoff, so as to provide a theoretical support and method for the construction of green roofs in urban districts.

Low impact development technologies for mitigating climate change:Summary and prospects

Many cities are adopting low impact development(LID)technologies(a type of nature-based solution)to sustainably manage urban stormwater in future climates.LIDs,such as bioretention cells,green roofs,and permeable pavements,are developed and applied at small-scales in urban and peri-urban settings.There is an interest in the large-scale implementation of these technologies,and therefore assessing their performance in future climates,or conversely,their potential for mitigating the impacts of climate change,can be valuable evidence in support of stormwater management planning.This paper provides a literature review of the studies conducted that examine LID function in future climates.The review found that most studies focus on LID performance at over 5 km2scales,which is quite a bit larger than traditional LID sizes.Most paper used statistical downscaling methods to simulate precipitation at the scale of the modelled LID.The computer model used to model LIDs was predominantly SWMM or some hybrid version of SWMM.The literature contains examples of both vegetated and unvegetated LIDs being assessed and numerous studies show mitigation of peak flows and total volumes to high levels in even the most extreme climates(characterized by increasing rainfall intensity,higher temperatures,and greater number of dry days in the inter-event period).However,all the studies recognized the uncertainty in the projections with greatest uncertainty in the LID’s ability to mitigate storm water quality.Interestingly,many of the studies did not recognize the impact of applying a model intended for small-scale processes at a much larger scale for which it is not intended.To explore the ramifications of scale when modelling LIDs in future climates,this paper provides a simple case study of a large catchment on Vancouver Island in British Columbia,Canada,using the Shannon Diversity Index.PCSWMM is used in conjunction with providing regional climates for impacts studies(PRECIS)regional climate model data to determine the relationship between catchment hydrology(with and without LIDs)and the information loss due to PCSWMM’s representation of spatial heterogeneity.The model is applied to five nested catchments ranging from 3 to 51 km2and with an RCP4.5 future climate to generate peak flows and total volumes in 2022,and for the period of 2020–2029.The case study demonstrates that the science behind the LID model within PC stormwater management model(PCSWMM)is too simple to capture appropriate levels of heterogeneity needed at larger-scale implementations.The model actually manufactures artificial levels of diversity due to its landuse representation,which is constant for every scale.The modelling exercise demonstrated that a simple linear expression for projected precipitation vs.catchment area would provide comparable estimates to PCSWMM.The study found that due to the spatial representation in PCSWMM for landuse,soil data and slope,slope(an important factor in determining peak flowrates)had the highest level of information loss followed by soil type and then landuse.As the research scale increased,the normalized information loss index(NILI)value for landuse exhibited the greatest information loss as the catchments scaled up.The NILI values before and after LID implementation in the model showed an inverse trend with the predicted LID mitigating performance.

Revealing the characteristics of dissolved organic matter in urban runoff at three typical regions via optical indices and molecular composition

Dissolved organic matter(DOM)plays a major role in ecological systems and influences the fate and transportation of many pollutants.Despite the significance of DOM,understanding of how environmental and anthropogenic factors influence its composition and characteristics is limited,especially in urban stormwater runoff.In this article,the chemical properties(pollutant loads,molecular weight,aromaticity,sources,and molecular composition)of DOM in stormwater extracted from three typical end-members(traffic,residential,and campus regions)were characterized by UV–visible(UV–vis)spectroscopy,excitationemission matrix spectroscopy combined with parallel factor analysis(EEM-PARAFAC),and ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry(UPLC-Q-TOF-MS).There are three findings:(1)The basic properties of DOM in stormwater runoff varied obviously from three urban fields,and the effect of initial flush was also apparent.(2)The DOM in residential areas mainly came from autochthonous sources,while allochthonous sources primarily contributed to the DOM in traffic and campus areas.However,it was mainly composed of terrestrial humic-like components with CHO and CHON element composition and HULO and aliphatic formulas.(3)The parameters characterizing DOM were primarily related to terrestrial source and aromaticity,but their correlations varied.Through the combination of optical methods and UPLC-Q-TOF spectrometry,the optical and molecular characteristics of rainwater are effectively revealed,which may provide a solid foundation for the classification management of stormwater runoff in different urban regions.

Removal of non-point pollutants from bridge runoff by a hydrocyclone using natural water head

A hydrocyclone using natural water head provided by bridge was operated for the treatment of stormwater runoff. The hydrocyclone was automatically controlled using electronic valve which is connected to a pressure meter. Normally the hydrocyclone was open during dry days, but it was closed after the capture of the first flush. The results indicated that the average pressure and the flow rate were directly affected by the rainfall intensity. The pressure head was more than 2 m when the rainfall intensity was above 5mm·h^-1. The percentage volume of underflow with high solids concentration decreased as the pressure and flow rate increased, but the percentage volume of overflow with almost no solids showed the opposite behavior. The total suspended solids （TSS） concentration ratio between the overflow and inflow （TSSover/TSSin） decreased as a function of the operational pressure, while the corresponding ratio of underflow to inflow （TSSunaer/TSSi,） increased. The TSS separation efficiency was evaluated based on a mass balance. It ranged from 25% to 99% with the pressure head ranging from 1.4 to 9.7 m, and it was proportional to pressure and flow rate. Normally, the efficiency was more than 50% when the pressure was higher than 2 m. The analysis of the water budget indicated that around 13% of the total runoff was captured by the hydrocyclone as a first flush, and this runoff was separated as underflow and overflow with the respective percentage volumes of 29% and 71%. The pollutants budget was also examined based on a mass balance. The results showed that the percentage of TSS, chemical oxygen demand （COD）, total nitrogen （TN）, and total phosphorus （TP） in underflow were 73%, 59%, 7.6%, and 49%, respectively. Thus, it can be concluded that the hydrocyclone worked well. It separated the first flush as solids-concentrated underflow and solids-absent overflow, and effectively reduced the runoff volume needing further treatment. Finally, four types of optional post treatment design are presented and compared.

Determination of urban runoff coefficient using time series inverse modeling

Runoff coefficient is an important parameter for the decision support of urban stormwater management. However, factors like comprehensive land-use type, variable spatial elevation, dynamic rainfall and groundwater elevation, make the direct estimation of runoff coefficient difficult. This paper presented a novel method to estimate the urban runoff coefficient using the inverse method, where observed time-series catchment outfall flow volume was employed as input for the water balance model and runoff coefficients of different catchments were treated as unknown parameters. A developed constrained minimization objective function was combined to solve the model and minimized error between observed and modeled outfall flow is satisfactory for the presenting of a set of runoff coefficients. Estimated runoff coefficients for the urban catchments in Shanghai downtown area demonstrated that practice of low impact design could play an important role in reducing the urban runoff.

Flow and mass balance analysis of eco-bio infiltration system

A structued stormwater infiltration system was developed and constructed at a university campus and monitoring of storm events was performed during a one- year operation period. The flow and pollutant mass balances were analyzed and the overall efficiency of the system was assessed. While significant positive correla- tions were observed among rainfall, runoff and discharge volume （R2= 0.93-0.99; p 〈 0.05）, there was no sig- nificant correlations existed between rainfall, runoff, discharge volume and pollutant load. The system was more effective in reducing the runoff volume by more than 50% for small storm events but the difference between the runoff and discharge volume was significant even with rainfall greater than 10ram. Results showed that the pollutant reduction rates were higher compared to the runoff volume reduction. Average pollutant reduction rates were in the range of 72% to 90% with coefficient of variation between 0.10 and 0.46. Comparable with runoff reduction, the system was more effective in reducing the pollutant load for small storm events, in the range of 80% to 100% for rainfall between 0 and 10mm; while 65% to 80% for rainfall between l0 and 20mm. Among the pollutant parameters, particulate matters was highly reduced by the system achieving only a maximum of 25% discharge load even after the entire runoff was completely discharged. The findings have proven the capability of the system as a tool in stormwater manage- ment achieving both flow reduction and water quality improvement.