Chemical characterization of urban stormwater: Traditional and emerging contaminants

Reduction of methane and nitrous oxide emissions from stormwater bioretention cells through microbial electrolytic cells

This study investigated the reduction of methane (CH4) and nitrous oxide (N2O) emissions from stormwater bioretention cells through microbial electrolytic cell (MEC), showing the largest reduction of 32.21 % (CH4) at 9.2 μA/m2 of current density and 56.16 % (N2O) at 3.5 μA/m2 of current density, compared with the corresponding in the control (0 μA/m2 of current density). Kinetic of CH4 and N2O emissions could be well fitted by Logistic model with high correlation coefficient (R2 > 0.9500) and model efficiency (ME > 0.95) but low relative root mean square error (RRMSE < 7.88). The increase of pmoA and polysaccharide (PS) were responsible for CH4 reduction, while N2O reduction was attributed to the decrease of nirS and the increase for nosZ and protein (PN), which could explain the lowest GWPd (10.67 mgCO2-eq/m2/h) at 3.5 μA/m2 of current density, suggesting that MEC could be promising for the reduction of CH4 and N2O emissions from bioretention cells.

Photoaged tire wear particles hinder the transport of Pb(II) in urban soils under acid rain: Experimental and numerical investigations

Rapid urbanization brought lots of serious environmental contamination, including the accumulation of heavy metals, acid rain, and the emission of tire wear particles (TWPs), with detrimental effects for terrestrial ecosystems. Nevertheless, how naturally aged TWPs affect the mobilization of heavy metals in soils under acid rain is still unclear. Here, we investigate the adsorption and transport mechanisms of Pb(II) co-existing with acid rainwater in soil-TWP mixtures via batch experiments, column experiments and modeling. Results showed that photoaged TWP significantly prolonged the Pb(II) adsorption equilibrium time (1 to 16 h) and enhanced the Pb(II) adsorption capacity of soils. Soil column profiles confirmed that TWP effectively boosted the initial accumulation of lead in the topsoil and thus impeded the downward transport of lead. The retardation factor (R) estimated by the linear two-site sorption model (TSM) fitting the Pb(II) breakthrough curves gradually increased from 1.098 to 16.38 in soils with TWP (0-10 %). Comparative results of linear or nonlinear TSM suggested nonlinear sorption replacing linear sorption as the main Pb(II) sorption mechanism under 1 % and 10 % TWP. This research provides significant insights into the implications of TWP on the Pb(II) retention behaviors and highlights the severer potential remobilization risks of Pb(II) in urban soils under different acid rain environments.

An integrated framework for stormwater management and life cycle assessment of rainwater harvesting: A comparative study of two underserved communities

Green infrastructure, which is designed to provide sustainable and resilient stormwater management solutions, inherently supports flood mitigation, pollution reduction, and a decentralized water supply. When proposing this type of infrastructure, it is important to identify environmental trade-offs related to their implementation. Our research focuses on a city-wide rain barrel (RB) deployment in northern and southern California, San Leandro and Imperial Beach, respectively. San Leandro and Imperial Beach are similar in that they are both low-lying coastal areas, containing a high percentage of residential areas with several census tracts listed as disadvantaged. A key difference is that San Leandro receives approximately 2.5 times the annual rainfall as Imperial Beach. This work utilizes PCSWMM for stormwater modeling to quantify captured stormwater, changes in conventional stormwater management (such as ocean outfall stormwater pumping), and reduced pollutant loading for RB deployment. Stormwater modeling is combined with Life Cycle Assessments (LCA) to quantify trade-offs in terms of Global Warming Potential (GWP), Human Toxicity Potential (HTP), Ecotoxicity Potential (EcoP) and Eutrophication Potential (EP). In Imperial Beach, RBs reduce GWP by 2.6 × 106 kg Carbon Dioxide Equivalent (CO2-Eq) and increase HTP by 3.8 × 106 kg Dichlorobenzene Equivalent (DCB-Eq). In San Leandro, GWP reduces by 1.3 × 107 kg CO2-Eq, and HTP increases by 4.7 × 106 kg DCB-Eq. In Imperial Beach, a reduction in runoff from captured rainfall results in a 44 % reduction of pollutant loading, while San Leandro sees a 27 % reduction. These reductions are equal to the reductions in EcoP and EP. Normalized per 1 m3 of collected stormwater, there is a lower reduction in GWP for Imperial Beach than San Leandro, and a higher contribution to HTP. This study advances current knowledge by quantifying RB benefits through multiple sustainability metrics, while comparing two underserved coastal California communities with distinct rainfall patterns. It demonstrates that while RBs reduce runoff and pollution, they also present environmental trade-offs, providing key insights for green infrastructure deployment.

From the highway to receiving water bodies: identification and simultaneous quantification of small microplastics (< 100 µm) in highway stormwater runoff

Highway stormwater (HSW) runoff is among the environment's most important sources of microplastics. This study aimed to characterize via vibrational spectroscopy and quantify SMPs (small microplastics < 100 µm) in HSW runoff from a trafficked highway entering a facility equipped with a filtration system and in those flowing out to the receiving water body near agricultural activities. Samples of the inlet runoff (from the highway) and outlet runoff (the discharge into the environment) were collected in different periods to investigate potential seasonal and spatial differences. The sampling, methodology, and analysis were thoroughly carried out to quantify and simultaneously identify SMPs via Micro-FTIR to obtain a specific novel dataset to assess the environmental quality of highway pollution. A significant difference between inlet and outlet samples was reported; the highest abundance in inlet samples was 39813 ± 277 SMPs L.1 (SW10 IN; average length of 77 µm), while the highest one in outlet samples was 15173 ± 171 SMPs L-1 (SW10 OUT; SMPs' average length of 63 µm). Polyamide 6 (PA 6) and High-Density Polyethylene (HDPE) were predominant. Our results show that these HSW treatment plants, designed for managing regulated pollutants, can intercept SMPs, improving the quality of HSW runoff discharged into the environment.

Towards sustainable water reuse: A critical review and meta-analysis of emerging chemical contaminants with risk-based evaluation, health hazard prediction and prioritization for assessment of effluent water quality

Reuse of treated wastewater is necessary to address water shortages in a changing climate. Sustainability of wastewater reuse requires reducing the environmental impacts of contaminants of emerging concern (CECs), but it is being questioned as CECs are not regulated in the assessment of effluent water quality for reuse both nationally in Sweden and at the broader European Union level. There is also a lack of details in this topic on which CECs to be addressed and methodologies to be used for assessing their environmental impacts. A better understanding of the ecological risks and health hazards of CECs associated with wastewater reuse will assist in the development of effective regulations on water reuse, (inter)nationally, as well as related treatment/monitoring guidelines. This review provides a list of specific chemical CECs that hinder sustainable wastewater reuse, and also demonstrates a holistic quantitative methodology for assessing, scoring and prioritizing their associated ecological risks and health hazards posed to the environment and humans. To achieve this, we compile information and concentrations of a wide range of CECs (∼15 000 data entries) identified in Swedish effluent wastewater from domestic (blackwater, greywater, mixture of both) and municipal settings, and further perform a meta-analysis of their potentials for 14 risk and hazard features, consisting of ecological risk, environmental hazard, and human health hazard. The features are then scored against defined criteria including guideline values, followed by score ranking for prioritization. This finally produces a unique list of chemical CECs from high to low priority based on risk- and hazard-evaluations. Out of the priority chemicals, 30, mainly pharmaceuticals, had risk quotient ≥ 1, indicating ecological risk, 16 had environmental hazard being persistent and mobile, and around 60 resulted in positive predictions for at least four human health hazards (particularly skin sensitization, developmental toxicity, hepatoxicity, and carcinogenicity). The 10 highest-priority chemicals (final score 2.3-3.0 out of 4.0) were venlafaxine, bicalutamide, desvenlafaxine, diclofenac, amoxicillin, clarithromycin, diethyltoluamide, genistein, azithromycin, and fexofenadine. Potential crop exposure to selected chemicals following one year of wastewater reuse for agricultural irrigation was also estimated, resulting in a range of 0.04 ng/kg (fluoxetine) to 1160 ng/kg (carbamazepine). Overall, our work will help focus efforts and costs on the critical chemicals in future (waste)water-related studies, such as, to evaluate removal efficiency of advanced treatment technologies and to study upstream source tracing (polluter-pays principle), and also in supporting policymakers to better regulate CECs for sustainable wastewater reuse in the future.

Developing simple indicators of nitrogen and phosphorus removal in constructed stormwater wetlands

Quantifying pollutant removal by stormwater wetlands requires intensive sampling which is cost-prohibitive for authorities responsible for a large number of wetlands. Wetland managers require simple indicators that provide a practical means of estimating performance and prioritising maintenance works across their asset base. We therefore aimed to develop vegetation cover and metrics derived from monitoring water level, as simple indicators of likely nutrient pollutant removal from stormwater wetlands. Over a two-year period, we measured vegetation cover and water levels at 17 wetlands and used both to predict nitrogen (N) and phosphorus (P) removal. Vegetation cover explained 48 % of variation in total nitrogen (TN) removal; with a linear relationship suggesting an approximate 9 % loss in TN removal per 10 % decrease in vegetation cover. Vegetation cover is therefore a useful indicator of TN removal. Further development of remotely-sensed data on vegetation configuration, species and condition will likely improve the accuracy of TN removal estimates. Total phosphorus (TP) removal was not predicted by vegetation cover, but was weakly related to the median water level which explained 25 % of variation TP removal. Despite weak prediction of TP removal, metrics derived from water level sensors identified faults such as excessive inflow and inefficient outflow, which in combination explained 50 % of the variation in the median water level. Monitoring water levels therefore has the potential to detect faults prior to loss of vegetation cover and therefore TN removal, as well as inform the corrective action required.

Repurposing spent biomass of vetiver grass used for stormwater treatment to generate biochar and ethanol

Stormwater pollution is a key factor contributing to water quality degradation, posing substantial environmental and human health risks. Although stormwater retention ponds, also referred to as wet ponds, are commonly implemented to alleviate stormwater challenges by reducing peak flow and removing suspended solids, their effectiveness in removing heavy metals and nutrients is limited. This study evaluated the performance of floating treatment platforms (FTPs) featuring vetiver grass (Chrysopogon zizanioides), a non-invasive, nutrient- and metal-accumulating perennial grass, in removing heavy metals (Cu, Pb, and Zn) and nutrients (P and N) in stormwater retention ponds. Furthermore, the potential for utilizing the spent vetiver biomass for generating biochar and bioethanol was investigated. The study was conducted in a greenhouse setup under simulated wet and dry weather conditions using pond water collected from a retention pond in Stafford Township, New Jersey, USA. Two FTPs with vetiver (vegetated FTPs) were compared with two FTPs without vetiver (non-vegetated FTPs), which served as controls. Results showed that the removal of heavy metals and nutrients by the FTPs with vetiver was significantly higher (p < 0.05) than the FTPs without vetiver. Notably, vetiver showed resilience to stormwater pollutants and hydroponic conditions, displaying no visible stress symptoms. The biochar and bioethanol generated from the spent vetiver exhibited desirable yield and quality, without raising concerns regarding pollutant leaching, indicated by very low TCLP and SPLP concentrations. This study provides compelling evidence that the implementation of vetiver-based FTPs offers a cost-effective and environment-friendly solution for mitigating stormwater pollution in retention ponds. Furthermore, the utilization of vetiver biomass for biofuel and biochar production supports clean production and fostering circular economy efforts.

Bioinspired stormwater control measure for the enhanced removal of truly dissolved polycyclic aromatic hydrocarbons and heavy metals from urban runoff

Stormwater harvesting (SWH) addresses the UN's Sustainable Development Goals (SDGs). Conventional stormwater control measures (SCMs) effectively remove particulate and colloidal contaminants from urban runoff; however, they fail to retain dissolved contaminants, particularly substances of concern like polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs), thereby hindering the SWH applicability. Here, inspired by protein folding in nature, we reported a novel biomimetic SCM for the efficient removal of dissolved PAHs and HMs from urban runoff. Lab-scale tests were conducted together with a more mechanistic investigation on how the contaminants were removed. By integrating hydrophobic organic chains with low-cost hydrophilic flocculant matrixes, our biomimetic flocculants achieved a 1.4-9.5 times removal of all detected dissolved PAHs and HMs, while enhancing the removal of a wide-spectrum of particulate and colloidal contaminants, compared to existing SCMs. Ecotoxicity, as indicated by newborn Daphnia magna as experimental organisms, was reduced from "acute toxicity" of the original runoff sample (toxic unit of ∼2.6) to "non-toxicity" (toxic unit < 0.4) of the treated water. The improved performance is attributed to the protein-folding-like features of the bioinspired flocculants providing: (i) stronger binding to PAHs (via hydrophobic association) and HMs (via coordination), and (ii) the ability of spontaneous aggregation. The bio-inspired approach in this work holds strong promise as an alternative or supplementary component in SCM systems, and is expected to contribute to sustainable water management practices in relation to SDGs.

Occurrence, bioaccumulation, fate, and risk assessment of emerging pollutants in aquatic environments: A review

Significant concerns on a global scale have been raised in response to the potential adverse impacts of emerging pollutants (EPs) on aquatic creatures. We have carefully reviewed relevant research over the past 10 years. The study focuses on five typical EPs: pharmaceuticals and personal care products (PPCPs), per- and polyfluoroalkyl substances (PFASs), drinking water disinfection byproducts (DBPs), brominated flame retardants (BFRs), and microplastics (MPs). The presence of EPs in the global aquatic environment is source-dependent, with wastewater treatment plants being the main source of EPs. Multiple studies have consistently shown that the final destination of most EPs in the water environment is sludge and sediment. Simultaneously, a number of EPs, such as PFASs, MPs, and BFRs, have long-term environmental transport potential. Some EPs exhibit notable tendencies towards bioaccumulation and biomagnification, while others pose challenges in terms of their degradation within both biological and abiotic treatment processes. The results showed that, in most cases, the ecological risk of EPs in aquatic environments was low, possibly due to potential dilution and degradation. Future research topics should include adding EPs detection items for the aquatic environment, combining pollution, and updating prediction models.

Removal and release of microplastics and other environmental pollutants during the start-up of bioretention filters treating stormwater

Untreated stormwater is a major source of microplastics, organic pollutants, metals, and nutrients in urban water courses. The aim of this study was to improve the knowledge about the start-up periods of bioretention filters. A rain garden pilot facility with 13 bioretention filters was constructed and stormwater from a highway and adjacent impervious surfaces was used for irrigation for ∼12 weeks. Selected plants (Armeria maritima, Hippophae rhamnoides, Juncus effusus, and Festuca rubra) was planted in ten filters. Stormwater percolated through the filters containing waste-to-energy bottom ash, biochar, or Sphagnum peat, mixed with sandy loam. Influent and effluent samples were taken to evaluate removal of the above-mentioned pollutants. All filters efficiently removed microplastics >10 µm, organic pollutants, and most metals. Copper leached from all filters initially but was significantly reduced in the biochar filters at the end of the period, while the other filters showed a declining trend. All filters leached nutrients initially, but concentrations decreased over time, and the biochar filters had efficiently reduced nitrogen after a few weeks. To conclude, all the filters effectively removed pollutants during the start-up period. Before being recommended for full-scale applications, the functionality of the filters after a longer period of operation should be evaluated.

Nutrient transport, shear strength and hydraulic characteristics of topsoils amended with mulch, compost and biosolids

Anthropogenic disturbance of soils can disrupt soil structure, diminish fertility, alter soil chemical properties, and cause erosion. Current remediation practices involve amending degraded urban topsoils lacking in organic matter and nutrition with organic amendments (OA) to enhance vegetative growth. However, the impact of OAs on water quality and structural properties at rates that meet common topsoil organic matter specifications need to be studied and understood. This study tested three commonly available OAs: shredded wood mulch, leaf-based compost, and class A Exceptional Quality stabilized sewage sludge (or biosolids) for nutrient (nitrogen and phosphorus) water quality, soil shear strength, and hydraulic properties, through two greenhouse tub studies. Findings showed that nitrogen losses to leachate were greater in the biosolids amended topsoils compared to leaf-compost, mulch amended topsoils, and control treatments. Steady-state mean total nitrogen (N) concentrations from biosolids treatment exceeded typical highway stormwater concentrations by at least 25 times. Soil total N content combined with the carbon:nitrogen ratio were identified to be the governing properties of N leaching in soils. Study soils, irrespective of the type of amendment, reduced the applied (tap) water phosphorus (P) concentration of ∼0.3 mg-P/L throughout the experiment. Contrary to the effects on N leaching, P was successfully retained by the biosolids amendment, due to the presence of greater active iron contents. A breakthrough mechanism for P was observed in leaf compost amended soil, where the effluent concentrations of P continued to increase with each rainfall application, possibly due to an saturation of soil adsorption sites. The addition of OAs also improved the strength and hydraulic properties of soils. The effective interlocking mechanisms between the soil and OA surfaces could provide soil its required strength and stability, particularly on slopes. OAs also improved soil fertility to promote turf growth. Presence of vegetative root zones can further reinforce the soil and control erosion.

Advancing rainwater treatment technologies for irrigation of urban agriculture: A pathway toward innovation

Urban agriculture (UA) has emerged for local food security since the 1960s. However, the access to sufficient and safe irrigation water remains a significant constraint. Municipal water supply, though commonly used in UA practices, proves unsustainable due to high costs, intensive energy consumption, and limited availability in many vacant urban spaces. In contrast, rainwater harvesting (RWH) exhibits a potential as a non-traditional water supply for urban farming. This article aims to provide insights into the advantages and challenges associated with RWH for UA irrigation, analyze existing low-cost RWH treatment technologies, and identify a visionary way toward innovative, new-generation RWH treatment processes in UA practices. Despite a promising water source, harvested rainwater is challenged for crop irrigation owing to the presence of various contaminants (e.g., waterborne pathogens, potentially toxic metals and metalloids, and synthetic organic chemicals). While established RWH treatment processes (e.g., first flush diversion, sedimentation, solar disinfection, chlorination, UV irradiation, granular filtration, and bio-sand filtration) can remove certain pollutants, they cannot offer viable treatment solutions for UA irrigation due to different technical, economic, and social restrictions. Particularly, their capacity to reliably remove contaminants of emerging concern in runoff remains limited or uncertain. Consequently, it is essential to develop next-generation RWH treatment technologies tailored specifically for UA irrigation. To this end, three fundamental principles are recommended. First, the focus should be on technically viable, low-cost, simple-operation, and easy-maintenance treatment technologies capable of simultaneously addressing traditional and emerging runoff contaminants, while minimizing the production of undesirable treatment byproducts. Second, advancing the understanding of the water, soil, and crop interactions enables the development of "right" RWH treatment processes for irrigation of "right" crops at a "right" place. Last, crop nutrients, if possible, are retained in rainwater to reduce the nutrient demand for crop production. The insights and perspectives have far-reaching implications for water conservation, stormwater management, and the integration of water, food, and energy systems within the urban environment.

The effects of heavy rain on the fate of urban and agricultural pollutants in the riverside area around weirs using multi-isotope, microbial data and numerical simulation

The increase in extreme heavy rain due to climate change is a critical factor in the fate of urban and agricultural pollutants in aquatic system. Nutrients, including NO3- and PO43-, are transported with surface and seepage waters into rivers, lakes and aquifers and can eventually lead to algal blooms. δ15N-NO3-, δ18O-NO3-, and δ11B combined with hydrogeochemical and microbial data for groundwater and surface water samples were interpreted to evaluate the fate of nutrients in a riverside area around weirs in Daegu, South Korea. Most of the ions showed similar concentrations in the groundwater samples before and after heavy rain while concentrations of major ions in surface water samples were diluted after heavy rain. However, Si, PO43-, Zn, Ce, La, Pb, Cu and a number of waterborne pathogens increased in surface water after heavy rain. The interpretation of δ11B, δ15N-NO3-, and δ18O-NO3- values using a Bayesian mixing model revealed that sewage and synthetic fertilizers were the main sources of contaminants in the groundwater and surface water samples. δ18O and SiO2 interpreted using the Bayesian mixing model indicated that the groundwater component in the surface water increased from 4.4 % to 17.9 % during the wet season. This is consistent with numerical simulation results indicating that the direct surface runoff and the groundwater baseflow contributions to the river system had also increased 6.4 times during the wet season. The increase in proteobacteria and decrease of actinobacteria in the surface water samples after heavy rain were also consistent with an increase of surface runoff and an increased groundwater component in the surface water. This study suggests that source apportionment based on chemical and multi-isotope data combined with numerical modeling approaches can be useful for identifying main hydrological and geochemical processes in riverside areas around weirs and can inform suggestions of effective methods for water quality management.

Interactions of particulate- and dissolved-phase heavy metals in a mature stormwater bioretention cell

Bioretention is an increasingly common stormwater control measure (SCM) for mitigation of stormwater quantity and quality. Studies from lab to field scale have shown successful removal of total metals from stormwater, especially Cu and Zn which are ubiquitous in the urban environment yet detrimental to aquatic ecosystems. While bioretention effectively removes particulate matter and particulate bound (PB) contaminants, removal performance of dissolved metals has been neglected in field studies. After approximately two decades of these systems being implemented, with a typical design-life of 20 years, performance of mature systems is unknown. This study examined the performance of a 16- to 18-year-old bioretention cell by characterizing Cu and Zn partitioning and removal. Flow-weighted composite samples of stormwater and bioretention effluent were collected and analyzed for total and dissolved metals. Size-fractioned road-deposited sediments (RDS) were collected and analyzed for metals and particle size distribution. The comparison of RDS and PB metals showed that PB-Zn was enriched in stormwater, indicating higher mobility of PB-Zn compared to PB-Cu. The mature bioretention system effectively removed particulates and PB-metals with average load reductions of 82% and 83%, respectively. While concentrations for dissolved metals were low (<40 μg/L), no significant difference between influent and effluent was observed. Effluent concentrations of total and dissolved Cu, total organic carbon, and particulates were not significantly different from those measured over 10 years ago at the site, while total Zn effluent concentration slightly increased. MINTEQ speciation modeling showed that Cu was approximately 100% bound with dissolved organic matter (DOM) in all bioretention effluent. While Zn was also mostly bound with DOM in effluent, some events showed free ionic Zn reaching concentrations in the same order of magnitude. Media amendments, maintenance, and monitoring of SCMs should be considered where further removal of dissolved metals is necessary for the protection of aquatic environments.

Review of emerging contaminants in green stormwater infrastructure: Antibiotic resistance genes, microplastics, tire wear particles, PFAS, and temperature

Green stormwater infrastructure is a growing management approach to capturing, infiltrating, and treating runoff at the source. However, there are several emerging contaminants for which green stormwater infrastructure has not been explicitly designed to mitigate and for which removal mechanisms are not yet well defined. This is an issue, as there is a growing understanding of the impact of emerging contaminants on human and environmental health. This paper presents a review of five emerging contaminants - antibiotic resistance genes, microplastics, tire wear particles, PFAS, and temperature - and seeks to improve our understanding of how green stormwater infrastructure is impacted by and can be designed to mitigate these emerging contaminants. To do so, we present a review of the source and transport of these contaminants to green stormwater infrastructure, specific treatment mechanisms within green infrastructure, and design considerations of green stormwater infrastructure that could lead to their removal. In addition, common removal mechanisms across these contaminants and limitations of green infrastructure for contaminant mitigation are discussed. Finally, we present future research directions that can help to advance the use of green infrastructure as a first line of defense for downstream water bodies against emerging contaminants of concern.

Migration and adsorption of naphthalene in road-deposited sediments from stormwater runoff: Impact of the particle size

In this study, we explored the impact of RDS particle size on the migration dynamics of RDS and naphthalene through rigorous wash-off experiments. The results illuminated that smaller RDS particles showed higher mobility in stormwater runoff. On the other hand, RDS particles larger than 150 μm showed migration ratios below 2 %, suggesting that naphthalene adsorbed on larger RDS primarily migrated in dissolved form. Furthermore, we investigated the migration behaviors of RDS and naphthalene under varied conditions, including rainfall intensity, duration, and naphthalene concentrations. Larger rainfall intensity promoted the naphthalene release from RDS, while long rainfall duration (≥10 min) impeded the migration velocities (≤2.91 %/5 min for RDS, and ≤3.32 %/5 min for corresponding naphthalene) of RDS and naphthalene. Additionally, higher naphthalene concentrations in RDS diminished migration ratios of dissolved naphthalene. Significantly, the maximum uptake of naphthalene on RDS was 6.02 mg/g by the adsorption Langmuir isotherm. Importantly, the adsorption process of naphthalene in RDS is primarily governed by the physical adsorption, as demonstrated by the successive desorption experiments, which showed the desorption rate of up to 87.32 %. Moreover, advanced characterizations such as XPS, FTIR and Raman spectra further confirmed the physical nature of the adsorption process. These findings may help the understanding of the migration behavior of other pollutants in urban surface particulates.

Influence of landscape patterns on nitrate and particulate organic nitrogen inputs to urban stormwater runoff

This study investigated the effect of the landscape pattern of permeable/impermeable patches on NO3--N and particulate organic nitrogen (PON) concentrations during stormwater runoff transport and their source contributions. Six landscape pattern indices, namely, mean proximity index (MPI), largest patch index (LPI), mean shape index (MSI), landscape shape index (LSI), connect index (CONNECT), and splitting index (SPLIT), were selected to reflect the fragmentation, complexity, and connectivity of permeable patches in urban catchments. The results show that lower fragmentation, higher complexity, and greater connectivity can reduce NO3--N concentrations in road runoff and drainage flow (i.e., the flow in the stormwater drainage network), as well as PON concentrations in road runoff. Further, the above landscape pattern is effective for mitigating the contributions of NO3--N and PON from road runoff. Low impact development (LID) can be incorporated with the landscape pattern of permeable/impermeable patches to mitigate nitrogen pollution in urban stormwater at the catchment scale by optimizing the spatial arrangement.

Performance of a gross pollutant trap-biofilter and sand filter treatment train for the removal of organic micropollutants from highway stormwater (field study)

This field study assessed the occurrence, event mean concentrations (EMCs), and removal of selected organic micro-pollutants (OMPs), namely, polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons (PHCs), nonylphenol (NP), 4-t-octylphenol (OP), and bisphenol A (BPA), in a gross pollutant trap (GPT)-biofilter/sand filter stormwater treatment train in Sundsvall, Sweden. The effects of design features of each treatment unit, including pre-sedimentation (GPT), sand filter medium, vegetation, and chalk amendment, were investigated by comparing the units' removal performances. Overall, the treatment train removed most OMPs from highway runoff effectively. The results showed that although the sand filter provided moderate (<50 % for phenolic substances) to high (50-80 % for PAHs and PHCs) removal of OMPs, adding a vegetated soil layer on top of the sand filter considerably improved the removal performance (by at least 30 %), especially for BPA, OP, and suspended solids. Moreover, GTP did not contribute to the treatment significantly. Uncertainties in the removal efficiencies of PAHs and PHCs by the filter cells increased substantially when the ratio of the influent concentration to the limit of quantification decreased. Thus, accounting for such uncertainties due to the low OMP concentrations should be considered when evaluating the removal performance of biofilters.

Enhanced Escherichia coli removal from stormwater with bermudagrass-derived activated biochar filtration systems

Stormwater treatment and reuse can alleviate water pollution and scarcity while current sand filtration systems showed low treatment performance for stormwater. For enhancing E. coli removal in stormwater, this study applied the bermudagrass-derived activated biochars (BCs) in the BC-sand filtration systems for E. coli removal. Compared with the pristine BC (without activation), the FeCl3 and NaOH activations increased the BC carbon content from 68.02% to 71.60% and 81.22% while E. coli removal efficiency increased from 77.60% to 81.16% and 98.68%, respectively. In all BCs, the BC carbon content showed a highly positive correlation with E. coli removal efficiency. The FeCl3 and NaOH activations also led to the enhancement of roughness of BC surface for enhancing E. coli removal by straining (physical entrapment). The main mechanisms for E. coli removal by BC-amended sand column were found to be hydrophobic attraction and straining. Additionally, under 105-107 CFU/mL of E. coli, final E. coli concentration in NaOH activated BC (NaOH-BC) column was one order of magnitude lower than those in pristine BC and FeCl3 activated BC (Fe-BC) columns. The presence of humic acid remarkably lowered the E. coli removal efficiency from 77.60% to 45.38% in pristine BC-amended sand column while slightly lowering the E. coli removal efficiencies from 81.16% and 98.68% to 68.65% and 92.57% in Fe-BC and NaOH-BC-amended sand columns, respectively. Moreover, compared to pristine BC, the activated BCs (Fe-BC and NaOH-BC) also resulted in the lower antibiotics (tetracycline and sulfamethoxazole) concentrations in the effluents from the BC-amended sand columns. Therefore, for the first time, this study indicated NaOH-BC showed high potential for effective treatment of E. coli from stormwater by the BC-amended sand filtration system compared with pristine BC and Fe-BC.

Submerged zone and vegetation drive distribution of heavy metal fractions and microbial community structure: Insights into stormwater biofiltration system

Biofiltration system is a widely used stormwater treatment option that is effective in removing heavy metals. The concentration and distribution of heavy metal fractions in biofiltration filter media, as well as the microbiota composition affected by the design parameters, are relatively novel concepts that require further research. A laboratory-scale column study was conducted to investigate the microbial community and the fractionation of heavy metals (Pb, Cu, Cr, and Cd) extracted from filter media samples, subjected to the presence of vegetation, submerged zone (SZ), and major environmental parameters (pH, water content). Sequential extractions revealed that, compared to the three other fractions (exchangeable fraction, reducible fraction, and oxidizable fraction), the residual fraction was the most represented for each metal (41 - 82 %). As a result, vegetation was found to reduce pH value, and significantly decrease the concentration of the exchangeable fraction of Pb in the middle layer, and the oxidizable fraction of Pb, Cu, Cd, and Cr in the middle and bottom layers (p < 0.05). The formation of an anoxic environment by submerged zone settlements resulted in a significant decrease in the concentration of reducible fractions and a significant increase in the concentration of oxidizable fractions for four heavy metals (p < 0.05). In addition, the analysis of the microbiota showed that the diversity and richness of microorganisms increased in the presence of SZ and plants. The dominant phylum in biofiltration was Proteobacteria, followed by Firmicutes, Bacteroidetes, Acidobacteria, and Actinobacteria as major phyla. Heavy metal fractions could regulate the structure of microbial communities in biofiltration. The findings of this study would enrich our understanding of the improvement of multi-metal-contaminated runoff treatment and highlight the impact of design parameters and heavy metal fractionation on microbial community structure in the biofiltration system.

Performance and microbial community of MBBRs under three maintenance strategies for intermittent stormwater treatment

Maintaining microbial activities is a critical problem for biological treatment processes of stormwater runoff because of its intermittent nature. In this study, the suitability of the moving bed biofilm reactor (MBBR) was assessed for stormwater treatment by long-term dry - rainy alternation operation. Three strategies to maintain microbial activities during the dry period, including keeping idle (MBBR_I), introducing river water throughout the period (MBBR_C), and ahead of a rainy day (MBBR_M), were investigated. COD and NH₄⁺-N removal efficiencies declined linearly from 94.2 % and 94.7 % to 51.7 % and 64.6 %, respectively, after the 61-day operation with microbial activity and biomass decreased. Introducing river water adversely affected the process performance as MBBR_C presented the highest declining rates of COD and NH₄⁺-N removal efficiencies. Most genera in MBBRs decayed and their microbial communities developed towards individualization, especially in MBBR_M because of its highest environmental variability. Keeping idle slightly alleviated the performance decline and formed a more stable microbial community structure. However, significantly deteriorating performance in all MBBRs after the long-term operation indicated that MBBRs were unsuitable for treating stormwater independently of intermittent nature.

Considerations for evaluating innovative stormwater treatment media for removal of dissolved contaminants of concern with focus on biochar

Stormwater from complex land uses is an important contributor of contaminants of concern (COCs) such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), Copper, and Zinc to receiving water bodies. A large portion of these COCs bind to particulate matter in stormwater, which can be removed through filtration by traditional media. However, the remaining dissolved COCs can be significant and require special attention such as engineered treatment measures and media. Biochar is a porous sorbent produced from a variety of organic materials. In the last decade biochar has been gaining attention as a stormwater treatment medium due to low cost compared to activated carbon. However, biochar is not a uniform product and selection of an appropriate biochar for the removal of specific contaminants can be a complex process. Biochars are synthesized from various feedstocks and using different manufacturing approaches, including pyrolysis temperature, impact the biochar properties thus affecting ability to remove stormwater contaminants. The local availability of specific biochar products is another important consideration. An evaluation of proposed stormwater control measure (SCM) media needs to consider the dynamic conditions associated with stormwater and its management, but the passive requirements of the SCM. The media should be able to mitigate flood risks, remove targeted COCs under high flow SCM conditions, and address practical considerations like cost, sourcing, and construction and maintenance. This paper outlines a process for selecting promising candidates for SCM media and evaluating their performance through laboratory tests and field deployment with special attention to unique stormwater considerations.

Phosphorus and Heavy Metals Removal from Stormwater Runoff Using Granulated Industrial Waste for Retrofitting Catch Basins

Phosphorus and heavy metals are washed off and transported with stormwater runoff to nearby surface water bodies resulting in environmental and human health risks. Catch basins remain one of the primary gateways through which stormwater runoff and pollutants from urban areas are transported. Retrofitting catch basins to enhance their phosphorus and heavy metal removal can be an effective approach. In this study, aluminum-based water treatment residual (WTR, a non-hazardous byproduct of the water treatment process) was granulated via a green method to serve as a sustainable filter material, called WTR granules, for enhancing the capabilities of catch basins to remove phosphorus and heavy metals. The WTR granules were field tested in a parking lot in Hoboken, New Jersey. Twelve storm events were monitored. The results showed that the WTR granules significantly (p < 0.05) reduced dissolved P, Cu, and Zn, as well as total P, Cu, Pb, and Zn concentrations in stormwater runoff without signs of disintegration. No flooding or water ponding was observed during the implementation. Results suggest the WTR granules are an inexpensive, green filter material that can be used for retrofitting catch basins to remove phosphorus and heavy metals effectively.

The influence of alkali-modified biochar on the removal and release of Zn in bioretention systems: Adsorption and immobilization mechanism

Generally, Zn in stormwater runoff is considered as low toxicity, but in the senarios of roads and zinc-based materials roof runoff, the concentration of Zn becomes extremely high and cannot be ignored. Bioretention systems are used to remove heavy metals from stormwater runoff, while Zn adsorption is insufficient by conventional filler and is prone to secondary release when exposed to acid rain or high salinity runoff. This study integrated batch experiments and density functional theory calculation to investigate the mechanisms of how KOH-modified biochar (KBC) influences the removal and release of Zn in bioretention systems. The results revealed that KBC adsorbed 89.0-97.5% Zn in the influent, the main adsorption mechanism were complexation and precipitation, and precipitation is more important. In addition, 67% of Zn was immoblized as the residual form by KBC. In acidic and saline runoff, KBC reduced Zn secondary release by 43.6% and 37.08% compared to the results in the absence of KBC, which was attributed to the convertion of most dissolved Zn in acidic and saline runoff into residual Zn. Therefore, KBC has a considerable application potential not only to decontaminate the runoff of roads and Zn-containing roofs, but also to deal with secondary Zn release in acid rain or under the treatment of snow-melting agents.

Spatiotemporal occurrence of phthalate esters in stormwater drains of Hong Kong, China: Mass loading and source identification

Urban stormwater is an important pathway for transporting anthropogenic pollutants to water bodies. Phthalate esters (PAEs) are endocrine disruptors owing to their estrogenic activity and potential carcinogenicity and their ubiquitous presence has garnered global interest. However, their transportation by urban stormwater has been largely overlooked. This study, for the first time, investigated 15 PAEs in stormwater from six major stormwater drains in the highly urbanized Hong Kong, a major metropolitan city in China. The results showed that PAEs were ubiquitous in the stormwater of Hong Kong, with total concentrations (∑₁₅PAEs) spanning from 195 to 80,500 ng/L. Bis(2-n-butoxyethyl) phthalate (DBEP), diisopentyl phthalate (DiPP), dicyclohexyl phthalate (DCHP) and di-n-pentyl phthalate (DnPP) were detected in stormwater for the first time. Spatial variations in PAEs were observed among different stormwater drains, possibly due to the different land use patterns and intensities of human activities in their respective catchments. The highest and lowest levels of ∑₁₅PAEs were found in Kwai Chung (3860 ± 1960 ng/L) and the Ng Tung River (672 ± 557 ng/L), respectively. Additionally, significantly higher concentrations of ∑₁₅PAEs in stormwater were found in the wet season (2520 ± 2050 ng/L) than in the dry season (947 ± 904 ng/L). Principal component analysis classified domestic and industrial origins as two important sources of PAEs in the stormwater of Hong Kong. Stormwater played a crucial role in transporting PAEs, with an estimated annual flux of 0.705-29.4 kg. Thus, possible stormwater management measures were proposed to protect the receiving environment and local ecosystems from stormwater.