Method for assessment of stormwater treatment facilities - Synthetic road runoff addition including micro-pollutants and tracer

Impact of green infrastructure on the mitigation of road-deposited sediment induced stormwater pollution

As a vital stormwater pollution source, the pollutants associated with road-deposited sediment (RDS) have become a growing concern in urban water management. Green infrastructure has exhibited great potential in stormwater pollution mitigation, but is not comprehensively understood yet due to the influences of complex RDS-associated pollutant migration processes (i.e., build-up, wash-off, and discharge). In this study, a city-scale hydraulic and water quality model was used to analyze the migration and removal processes of four RDS-associated pollutants (total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP)) under different hydrological patterns, land-cover types, and green infrastructure installation locations. Results show that the antecedent dry-weather period was the main factor influencing RDS build-up, while the precipitation pattern strongly impacted RDS wash-off, discharge, and removal. The downstream-installed green infrastructures reduced the RDS-induced stormwater pollution by up to 68% and relieved the pollution-mitigation pressure of the studied drainage networks by almost 50%. The TSS and COD removal rates were higher (62.22-68.09%) near green space, while those of TN and TP were higher around buildings and roads (40.00-62.50%). Sensitivity analysis indicated that seven parameters regarding the surface layer characteristics and soil texture class strongly impacted the pollution-mitigation performance among the 31 technical parameters of green infrastructure. The results of this study would assist urban water management by optimizing green infrastructure for stormwater pollution mitigation.

Robustness analysis of storm water quality modelling with LID infrastructures from natural event-based field monitoring

Sponge city construction (SCC) in China, as a new concept and a practical application of low-impact development (LID), is gaining wide popularity. Modelling tools are widely used to evaluate the ecological benefits of SCC in stormwater pollution mitigation. However, the understanding of the robustness of water quality modelling with different LID design options is still limited due to the paucity of water quality data as well as the high cost of water quality data collection and model calibration. This study develops a new concept of 'robustness' measured by model calibration performances. It combines an automatic calibration technique with intensive field monitoring data to perform the robustness analysis of storm water quality modelling using the SWMM (Storm Water Management Model). One of the national pilot areas of SCC, Fenghuang Cheng, in Shenzhen, China, is selected as the study area. Five water quality variables (COD, NH3-N, TN, TP, and SS) and 13 types of LID/non-LID infrastructures are simulated using 37 rainfall events. The results show that the model performance is satisfactory for different water quality variables and LID types. Water quality modelling of greenbelts and rain gardens has the best performance, while the models of barrels and green roofs are not as robust as those of the other LID types. In urban runoff, three water quality parameters, namely, SS, TN and COD, are better captured by the SWMM models than NH₃-N and TP. The modelling performance tends to be better under heavy rain and significant pollutant concentrations, denoting a potentially more stable and reliable design of infrastructures. This study helps to improve the current understanding of the feasibility and robustness of using the SWMM model in sponge city design.

Combined dual-size foam glass media filtration process with micro-flocculation for simultaneous removal of particulate and dissolved contaminants in urban road runoff

In this study, a combined media filtration process with micro-flocculation (CMF) was developed, to simultaneously treat particulate and dissolved contaminants in urban road runoff. Dual-size foam glass media with stone and sand layers were applied and the efficiency of road runoff treatment was investigated according to filtration and micro-flocculation under various experimental conditions (stone/sand layer ratio, linear velocity, and coagulant types). Moreover, the removal efficiencies of suspended solids (SS), phosphorus, organic carbon, and heavy metals (Zn, Cu, Pb, Cd) by CMF were evaluated. The removal rate of SS was maintained to be above 84.1% for 1 h filtration by the dual-size foam glass, regardless of increasing pressure. The removal of phosphorus by micro-flocculation was more suitable in alum than ferric due to a higher initial floc growth rate and an increased particle size. The performance of the CMF was significantly improved over media filtration only process (MF) in removing both particulate and dissolved contaminants. The removal efficiency of all particulate pollutants by CMF was found to be more than 90%, and notably, the dissolved phosphorus, which was mostly not removed by MF, was also removed by 97.4%. Meanwhile, the backwash efficiency of CMF was half that of MF. Physical removal mechanisms, such as internal diffusion, dominated MF, whereas chemical removal mechanisms, such as adsorption and surface precipitation, dominated CMF. These results show the potential of the CMF process for the treatment of urban road runoff and identify the removal mechanisms of the filtration process that use micro-flocculation with dual-size foam glass.

Characteristics of particle size distribution and related contaminants of highway-deposited sediment, Maanshan City, China

Road-deposited sediment (RDS) has been identified as both the source and sink of various pollutants. In this study, the highway-deposited sediment (HDS) in Spring, Summer, Autumn and Winter was characterized. On average, the mass proportions of particles with the size of 830-4750 μm, 500-830 μm, 250-500 μm, 150-250 μm, 63-150 μm and < 63 μm were 23.6 ± 8.6%, 16.9 ± 3.4%, 28.4 ± 3.5%, 10.0 ± 4.3%, 15.7 ± 5.8% and 5.3 ± 2.0%, respectively, wherein the HDS of 63-830 μm accounted for 71% of the total mass load. It was observed that the particle size distribution of HDS could be described using the gamma distribution function based on gravimetric and cumulative basis (R² (determination coefficient) = 0.9960-0.9995). The bulk pollutant contents of HDS showed seasonal variation with the mean of COD (chemical oxygen demand), nitrogen, phosphorus, Zn (zinc), Pb (lead) and Cd (cadmium) as 57 g/kg, 839 mg/kg, 97 mg/kg, 627 mg/kg, 110 mg/kg and 1.00 mg/kg and the highest COD of 83 g/kg in Autumn, nitrogen 1164 mg/kg Autumn, phosphorus 133 mg/kg Winter, Zn 801 mg/kg Summer, Pb 133 mg/kg Spring and the highest Cd of 1.36 mg/kg in Summer, respectively. The contents of Zn, Pb and Cd in HDS were significantly above their local soil background values. Moreover, the size fractional pollutant contents overall increased as particles' size increased. Averagely, 40-52% pollutant loads were associated with the particles < 250 μm, which can be moved easily by runoff. This study suggests that the behaviors of HDS different from city RDS should be considered as nonpoint source pollution control is performed.

The Impact of Temperature on the Removal of Inorganic Contaminants Typical of Urban Stormwater

Appropriate management of urban stormwater requires consideration of both water quantity, resulting from flood control requirements, and water quality, being a consequence of contaminant distribution via runoff water. This article focuses on the impact of temperature on the efficiency of stormwater treatment processes in permeable infiltration systems. Studies of the removal capacity of activated carbon, diatomite, halloysite, limestone sand and zeolite for select heavy metals (Cu and Zn) and biogenes (NH4-N and PO4-P) were performed in batch conditions at 3, 6, 10, 15, 22, 30 and 40 °C at low initial concentrations, and maximum sorption capacities determined at 3, 10, 22 and 40 °C. A decrease in temperature to 3 °C reduced the maximum sorption capacities (Qmax) of the applied materials in the range of 10% for diatomite uptake of PO4-P, to 46% for halloysite uptake of Cu. Only the value of Qmax for halloysite, limestone sand and diatomite for NH4-N uptake decreased slightly with temperature increase. A positive correlation was also observed for the equilibrium sorption (Qe) of Cu and Zn for analyses performed at low concentrations (with the exception of Zn sorption on limestone sand). In turn, for biogenes a rising trend was observed only in the range of 3 °C to 22 °C, whereas further temperature increase caused a decrease of Qe. Temperature had the largest influence on the removal of copper and the smallest on the removal of phosphates. It was also observed that the impact of temperature on the process of phosphate removal on all materials and ammonium ions on all materials, with the exception of zeolite, was negligible.

Filtering Capability of Porous Asphalt Pavements

The objective of this study is to assess the filtering capability of porous asphalt pavement models and the quality of rainwater filtered by such models. Three slabs of porous asphalt mixtures and two models composed of porous layers that resulted in porous pavement structures were produced. Data were collected in two phases: using rainwater directly from the sky and then using stormwater runoff collected from a street. Parameters such as pH, dissolved oxygen, ammonia, phosphorus, nitrite, aluminium, chromium, copper, zinc, and iron were measured. For both rainwater and stormwater runoff quality analyses, there was an increase in the concentration of the following parameters: phosphorus, iron, aluminium, zinc, nitrite, chromium, copper, and pH; there was no significant variation in the concentration of dissolved oxygen; and there was a decrease in ammonia in one of the models. However, the concentrations of only phosphorus and aluminium exceeded the limits established by the Brazilian National Environmental Council and National Water Agency for the use of non-potable water. The models were capable of filtering rainwater and stormwater runoff, and reducing the concentration of ammonia. It can be concluded that it is possible to collect stormwater runoff from porous asphalt surfaces and porous asphalt pavements. Porous asphalt pavements are able to filter out certain pollutants from stormwater runoff and rainwater, and were shown to be an alternative to supply rainwater for non-potable uses and to recharge the water table.