Hydraulic and pollutant removal performance of stormwater filters under variable wetting and drying regimes.

Biofiltration systems are an effective stormwater treatment technology. However, their robustness is yet to be tested, particularly their performance following extended dry periods. The hydraulic and treatment performance of five different non-vegetated, soil-based filters under varying periods of inundation and drying was assessed. The infiltration capacity of the filters decreased during wet periods and increased following dry periods, most probably due to swelling and shrinkage of the filter media. Treatment of sediment, heavy metals and phosphorus was not influenced by the wetting and drying regime. However, outflow concentrations of nitrogen were significantly higher upon re-wetting following extended dry periods compared with wet periods. This result has implications for current design practices, as these nitrogen pulses could negatively impact the ecological health of downstream receiving waters.     

Filter media for stormwater treatment and recycling: the influence of hydraulic properties of flow on pollutant removal.

Improved urban water management in Australia is of national importance. Water resources are stretched and urban runoff is a recognized leading cause of degradation of urban waterways. Stormwater recycling is an option that can contribute to easing these problems. Biofilters are effective structural stormwater pollution control measures with the potential for integration into stormwater treatment and recycling systems. However, premature clogging of biofilters is a major problem, with resulting decreased infiltration capacity (and hence the volume of stormwater the system can detain) and increased detention time. This paper presents preliminary findings with respect to the effect of clogging on pollutant removal efficiency in conventional stormwater filter media. A one-dimensional laboratory rig was used to investigate the impact of clogging on pollutant removal efficiency in a conventional biofiltration filter media (gravel over sand). Both the individual gravel layer and the overall multi-filter were highly efficient at removing suspended solids and particulate-associated pollutants. This removal efficiency was consistent, even as the filters became clogged. Removal of dissolved nutrients was more variable, with little reduction in concentrations overall. Although preliminary, these results challenge the concept that increased detention time improves the treatment performance of stormwater filtration systems.     

Statistical analysis of pollution in stormwater infiltration basins.

In order to characterize soil pollution in stormwater infiltration basins, four basins of the Lyon area were selected and sampled. Altogether, 66 soil samples were collected. Each sample was analyzed for pH, cationic exchange capacity, particle size distribution, total organic carbon, total nitrogen, total phosphorus, metals, total hydrocarbons and polycyclic aromatic hydrocarbons (PAHs). Data was explored in a classic way (soil profiles) and using multivariate analysis techniques. Two methods were applied: Principal Component Analysis (PCA) and Cluster Analysis (CA). Main results are presented in this paper. Pollutant concentrations decrease rapidly with depth while pH and grain size increase. Sustainable concentrations are reached at a 50-cm depth, even after 21 years of operation. Multivariate analysis shows how pollution affects each sampling depth.     

Monitor-based evaluation of pollutant load from urban stormwater runoff in Beijing.

As a major pollutant source to urban receiving waters, the non-point source pollution from urban runoff needs to be well studied and effectively controlled. Based on monitoring data from urban runoff pollutant sources, this article describes a systematic estimation of total pollutant loads from the urban areas of Beijing. A numerical model was developed to quantify main pollutant loads of urban runoff in Beijing. A sub-procedure is involved in this method, in which the flush process influences both the quantity and quality of stormwater runoff. A statistics-based method was applied in computing the annual pollutant load as an output of the runoff. The proportions of pollutant from point-source and non-point sources were compared. This provides a scientific basis for proper environmental input assessment of urban stormwater pollution to receiving waters, improvement of infrastructure performance, implementation of urban stormwater management, and utilization of stormwater.     

Sensitivity to experimental data of pollutant site mean concentration in stormwater runoff.

Urban wet weather discharges are known to be a great source of pollutants for receiving waters, which protection requires the estimation of long-term discharged pollutant loads. Pollutant loads can be estimated by multiplying a site mean concentration (SMC) by the total runoff volume during a given period of time. The estimation of the SMC value as a weighted mean value with event runoff volumes as weights is affected by uncertainties due to the variability of event mean concentrations and to the number of events used. This study carried out on 13 catchments gives orders of magnitude of these uncertainties and shows the limitations of usual practices using few measured events. The results obtained show that it is not possible to propose a standard minimal number of events to be measured on any catchment in order to evaluate the SMC value with a given uncertainty.     

Zinc-sulphate-heptahydrate coated activated carbon for microbe removal from stormwater

There is a need to develop effective stormwater filters for passive (without any addition of chemicals or energy) and effective removal of pathogens in order to mainstream stormwater harvesting. This study focuses on the development of coated granular activated carbon (GAC) filtration material in order to develop filters for effective removal of pathogens from urban stormwater. Several laboratory trials were performed to gauge the effectiveness of the filters, which use a mixture of the zinc-sulphate-heptahydrate coated GAC and sand, on the removal of Escherichia coli (E. coli) from semi-natural stormwater. On average, a 98% removal of the inflow concentration of E. coli was achieved. Furthermore, there was also an improvement of approximately 25% in the removal of phosphorous. However, it was found that the treated material was leaching zinc. It was important to determine whether the observed removal of E. coli was indirectly caused by the sampling methodology. The results showed that the inactivation of the E. coli in the collected sample was small compared with the inactivation which actually occurred within the filter. This provides much promise to the filter, but the presence of zinc in the outflow demonstrates the need for further investigation into the stabilisation of the coating process.     

Chemical hazard identification and assessment tool for evaluation of stormwater priority pollutants.

Assessment of chemical hazards is a critical issue, which have to be dealt with when evaluating different strategies for sustainable handling of stormwater. In the present study, a methodology for identifying the most critical and representative chemical pollutants was developed. A list of selected stormwater priority pollutants (SSPP-list) is the out-put from the procedure. Two different strategies for handling of stormwater were considered; discharge into a surface water recipient and infiltration. However, the same methodology can be used for other types of wastewater and other strategies for handling and treatment. A literature survey revealed that at least 656 xenobiotic organic compounds (XOCs) could be present in stormwater. In the next step, 233 XOCs were evaluated with respect to the potential for being hazardous towards either aquatic living organisms or humans, or causing technical or aesthetical problems. 121 XOCs were found have at least one of these negative effects, while 26 XOCs could not be assessed due to the lack of data. The hazard assessment showed that 40 XOCs had a PEC/PNEC ratio above one., e.g. they should be considered as priority pollutants. The final step is the expert judgement, which resulted in a final SSPP-list containing 16 selected priority pollutants.     

Modelling non-structural best management practices--focus on reductions in stormwater pollution.

This paper describes a modelling approach for evaluating the efficiency of different non-structural best management practices for stormwater management. A scenario with a set of source reduction practices was simulated using the substance flow model SEWSYS for an urban catchment in the city of G?teborg, Sweden. The scenario is based on a hypothetical control program that includes prevention, education and regulations. The simulation shows relatively high reductions of copper and PAH, 77% and 50%, respectively. The reduction in copper is mainly due to less copper roof corrosion and brake wear, while reduced road wear has the greatest effect for PAH. An important result from this study is that the nonstructural BMPs applied did not give a sufficient reduction in pollution to meet the desirable environmental quality criteria. To meet these criteria, additional BMPs must be implemented, preferably a combination of both non-structural and structural measures.     

A metamodel for stormwater detention basins design.

The aim of storm basins is to protect urban areas against some predefined risk of exceeding a given value of downstream runoff, or a risk of overflow for a bounded storage capacity. This risk results from the combination of a natural hazard and hydraulic properties. The correct way to address this issue is to use a stochastic rainfall model, but it may require unavailable data and be cumbersome to use in the framework of an optimisation procedure. We give the end user a way to by-pass this step, by means of a metamodel. The problem is to calculate the parameters of the probability density function (pdf) of outputs as a function of the pdf of inputs and of the parameters of the dynamic deterministic system between inputs and outputs. We propose to apply a metamodel, which is a new way of designing approximate but generic derived distribution, based on conditional probabilities. For application to dimensioning of basins, the determination of the parameter(s) corresponding to an acceptable risk simply consists of solving an algebraic equation representing the metamodel. The methodology needs usual rainfall statistics and a specific parameter inferred from analysis of storms, or supposed to have a regional value.     

Pollutant removal efficiency of alternative filtration media in stormwater treatment.

Sorption experiments were used to assess the ability of various materials (sand, compost, packing wood, ash, zeolite, recycled glass and Enviro-media) to remove heavy metal contaminants typically found in stormwater. Compost was found to have the best physicochemical properties for sorption of metal ions (Cu, Zn and Pb) compared with sand, packing wood, ash, zeolite and Enviro-media. The compost sorption of these metal ions conformed to the linear form of the Langmuir adsorption equation with the Langmuir constants (q,) for Zn(ll) being 11.2 mg/g at pH 5. However, compost was also found to leach a high concentration of dissolved organic carbon (DOC, 4.31 mg/g), compared with the other tested materials. Various combinations of sand, compost and other materials were observed to have excellent heavy metal removal (75-96% of Zn and 90-93% of Cu), with minimal DOC leaching (0.0013-2.43 mg/g). The sorption efficiency of the different Enviro-media mixes showed that a combination of traditional (sand) and alternative materials can be used as an effective medium for the treatment of dissolved metal contaminants commonly found in stormwater. The application of using recycled organic materials and other waste materials (such as recycled glass) also provides added value to the products life cycle.     

Applicability of modelling tools in watershed management for controlling diffuse pollution.

Diffuse pollution is hard to analyze, control and manage by its nature. Watershed models and Geographical Information Systems (GIS) are recently developed tools that aid analysis of diffuse sources of pollution. However, their applications are not always easy and straightforward. Turkey is a typical example of a mountainous country rich in rivers and streams. Due to the complex geomorphology, land-use and agricultural practices in most of the watersheds in Turkey, modelling, analyzing and managing diffuse pollution has been a challenge. The complex watershed structure forces the modellers to work with spatially high resolution data. Apart from the data, the models themselves may also cause operational problems. These issues and their probable solutions form the basis of the discussions in this paper. It acts as a guideline for modelling and analyzing diffuse pollution by emphasizing the referred problems and difficulties. Design of an Information Technology-based system tool for watershed and/or water quality modelling, which would be suitable for countries having watersheds with similar structure and problems to those of Turkey, is also outlined.     

Characteristics of urban run-off derived sediments captured by proprietary flow-through stormwater interceptors.

Sediment entrained in urban run-off is acknowledged as being an important carrier of pollutants. The paper reports on the physical and chemical characteristics of sediments captured by six installations of a proprietary interceptor device. The sites, located in the United Kingdom and the Republic of Ireland, were selected to represent a range of urban contexts. Particle D(50) values were found to range from 7 to 112 mum, corresponding with ranges reported for stormwater ponds. Heavy metal and hydrocarbon concentrations were also found to vary, with the highest corresponding to the most established and heavily trafficked sites. Further to confirming the ability of the interceptor to remove contaminated sediments, useful insights are provided into the interrelation between sediment characteristics and site conditions.     

Comparison of pollutant loading estimation using different land uses and stormwater characteristics in Ballona Creek Watershed.

Estimation of stormwater pollutant loads using land use based models has been widely used for establishing regulations and management practices. This approach requires land use information to assign the imperviousness or runoff coefficients (RC) and event mean concentrations (EMCs) for the pollutants of interest. This simplistic approach is useful to estimate the total mass emissions. However, different research groups have used various parameters based upon similar data sources, and there are very few validations using actual field data. This study compares the assumptions, methodologies and results of several, independent modelling efforts, and functions as a quality and sensitivity study of the methodologies. The similarity or differences of the various model results serve as a qualitative indicator of the state of art for this type of stormwater modelling.     

Dynamic actor network analysis for diffuse pollution in the province of North-Holland.

Diffuse pollution problems involve numerous different organizations and this requires decision makers to involve different actors if they want to develop policies that have a chance of being implemented effectively. A first step in such interactive policy development would be to gain an overview of the different actors involved in diffuse pollution problems, as well as their views on the problem, their interests and their means to influence policy development and implementation. Dynamic Actor Network Analysis (DANA) offers a method that helps analysts in providing such an overview, and the use of this method is explored through its application to a case in the Dutch province of North Holland. The described case specifically focuses on the use of herbicides in public space and involves actors from regional water management authorities, municipalities and private sector users. An important finding is that there is an imbalance in the perceptions of actors that needs to be addressed by water management authorities. The paper concludes that DANA is a promising tool for offering new and useful insights to decision makers, although more practical experience is needed to better assess the utility of this analysis tool.     

Defining urban diffuse pollution loadings and receiving water hazard.

The use of unit area loading approaches to address the requirements of the US Clean Water Act (CWA) and the EU Water Framework Directive (WFD) to identify and manage diffuse urban pollution sources is outlined. Issues relating to traditional volume-concentration probabilistic modelling are highlighted and the robustness of total maximum daily load (TMDL) approaches is discussed. A hazard assessment methodology for catchment scale identification of source area pollutant loadings and receiving water ecological impacts is developed based on urban land use activities.     

The next step--incorporating diffuse pollution abatement into watershed management.

The majority of adverse changes in watersheds impairing water quality occurred over a period of thirty to more than one hundred years. In many areas over a period of about 80 years more than 90% of the wetlands were drained, cultivated and converted to agricultural and urban uses. This conversion changed the redox status of the soils and soil cover with a concurrent large increase of suspended solids, dissolved organic matter, nitrogen, and phosphate loads from the watersheds located in the affected regions. The question whether these adverse changes are reversible by reduction or discontinuation of excessive inputs of pollutants came to light and has been analyzed recently after the political changes in Eastern Europe. Reliable dynamic long term models that would describe interactions between nutrient inputs, outputs, storage etc., have not been developed yet. It is becoming apparent that it may take longer for the watersheds to recover after nutrient loads to surface and groundwater are reduced if remedial measures are gradually implemented.     

Contaminant removal and hydraulic conductivity of laboratory rain garden systems for stormwater treatment

In order to evaluate the influence of substrate composition on stormwater treatment and hydraulic effectiveness, mesocosm-scale (180 L, 0.17 m(2)) laboratory rain gardens were established. Saturated (constant head) hydraulic conductivity was determined before and after contaminant (Cu, Zn, Pb and nutrients) removal experiments on three rain garden systems with various proportions of organic topsoil. The system with only topsoil had the lowest saturated hydraulic conductivity (160-164 mm/h) and poorest metal removal efficiency (Cu ≤ 69.0% and Zn ≤ 71.4%). Systems with sand and a sand-topsoil mix demonstrated good metal removal (Cu up to 83.3%, Zn up to 94.5%, Pb up to 97.3%) with adequate hydraulic conductivity (sand: 800-805 mm/h, sand-topsoil: 290-302 mm/h). Total metal amounts in the effluent were <50% of influent amounts for all experiments, with the exception of Cu removal in the topsoil-only system, which was negligible due to high dissolved fraction. Metal removal was greater when effluent pH was elevated (up to 7.38) provided by the calcareous sand in two of the systems, whereas the topsoil-only system lacked an alkaline source. Organic topsoil, a typical component in rain garden systems, influenced pH, resulting in poorer treatment due to higher dissolved metal fractions.     

The assessment of diffuse pollution from acid-mine drainage using an updated and revised diatom assessment procedure as an added-value bio-monitoring tool.

Three data sources (physico-chemistry, bio-monitoring and eco-toxicology) are currently used in South Africa to establish environmental water quality conditions. Environmental water quality in turn is key information required for the "ecological reserve determination" of river reaches. Bio-monitoring in South Africa has been limited in recent times mostly to the use of the SASS procedure which relies on invertebrates only. This paper describes the re-introduction of a diatom-based water quality assessment as an added-value bio-monitoring tool. A specific example is discussed citing the response of diatom assemblages to diffuse pollution from acid mine drainage and how effective diatoms are as indicators of ecological integrity and river recovery measured downstream of the area of impact. The advantages of applying this bio-monitoring technique over other biological measures are presented in the context of technological advances in rapid image processing, species identification and software applications of diatom-based water quality indices. The valuable records of the diatom assemblages of the past, held in the South African Diatom Collection at the CSIR (KwaZulu-Natal), can now be accessed and interpreted as historical environmental water quality reference points for several rivers in South Africa.     

香港维多利亚港三维污染精细预报模型研究

：本文把研究近海水域水质污染与控制的三维精细预报系统作为目标，在分析近海环境中各种物理、化学和生物现象的基础上，针对近海水域水污染的特点，选定一个包含有二十多个状态变量及其相互作用的三维非线性系统作为研究和模拟对象，建立一个统一考虑物理、化学和生物等过程综合作用的近海水域三维水动力学和水质的精细模型，并成功地应用于香港维多利亚港的水质模拟。     

Development and investigation of a pollution control pit for treatment of stormwater from metal roofs and traffic areas.

Source control by on-site retention and infiltration of stormwater is a sustainable and proven alternative to classical drainage methods. Unfortunately, sedimentary particles and pollutants from drained surfaces cause clogging and endanger soil and groundwater during long-term operation of infiltration devices. German water authorities recommend the use of infiltration devices, such as swales or swale-trench-systems. Direct infiltration by underground facilities, such as pipes, trenches or sinks, without pretreatment of runoff is generally not permitted. Problems occur with runoff from metal roofs, traffic areas and industrial sites. However, due to site limitations, underground systems are often the only feasible option. To overcome this situation, a pollution control pit was developed with a hydrodynamic separator and a multistage filter made of coated porous concrete. The system treats runoff at source and protects soil, groundwater and receiving waterways. Typically, more than 90% of the pollutants such as sedimentary particles, hydrocarbons and heavy metals can be removed. Filters have been developed to treat even higher polluted stormwater loads from metal roofs and industrial sites. The treatment process is based on sedimentation, filtration, adsorption and chemical precipitation. Sediments are trapped in a special chamber within the pit and can be removed easily. Other pollutants are captured in the concrete filter upstream of the sediment separator chamber. Filters can be easily replaced.