Stormwater Pollution Research Articles

Stratification and its consequences in two constructed urban stormwater wetlands

Stratification in constructed urban stormwater wetlands is one of the fundamental physical processes that affect hydrodynamics, transport and fate of stormwater pollutants. Adverse effects of stratification include decreasing pollutant retention capacity, causing the water at lower depths to become anoxic, degrading water quality and increasing stress on the downstream aquatic communities. The current study reports on a comprehensive field monitoring program of stratification and hydrodynamics in two ice-free seasons (May – October) in two constructed urban stormwater wetlands in Calgary, Canada, with different inlet, outlet, morphometric and vegetation designs. Despite their small sizes of 0.5 and 1.2 ha and shallow water depths of 0.8 m, stratification was strong and persistent in the wetlands. The response of stratification and mixing to atmospheric forcings (e.g., air temperature, atmospheric instability, rainfall depth, wind speed) and the impact of design characteristics (inlet/outlet design, water depth, surface area and aquatic vegetation) were examined and discussed. Thermal stratification, defined as a vertical temperature gradient >1 °C/m, was found to be significantly higher (up to ten times) near the inlets and last longer (up to twice) than in the main cells and the outlet basins due to the relatively cold summer inflows. The wetland with twice the permanent water volume and surface area and half the length-to-width ratio had denser submerged aquatic vegetation, higher (by up to 2 °C) water temperature and more severe (up to eight times) thermal stratification. Strong densimetric stratification and low wind stress on the water surface caused hypoxic conditions near the bed, potentially adversely affecting water quality and downstream aquatic communities.

Stormwater subsurface gravel wetland hydraulics, phosphorus retention, and chloride dynamics in cold climates

The stormwater treatment performance of an increasingly popular horizontal subsurface-flow gravel wetland design in the northeastern United States was characterized by poor phosphorus retention and negligible impacts on chloride transport.

An Adaptive Toolkit for Projecting the Impact of Green Infrastructure Provisions on Stormwater Runoff and Pollutant Load-A Case Study on the City of Galena Park, Texas, USA.

The implementation of green infrastructure in retrofit projects to reduce flooding and pollution is a significant challenge in space- constrained and overly developed communities which also have complex underground utility systems. To overcome this challenge, the authors have developed an adaptive green infrastructure toolkit that can be tailored by both on-ground spatial size and underground depth of obstruction. This study aims to assess the effectiveness of this toolkit in mitigating flooding and non-point source pollutants by demonstrating the case of the city of Galena Park, Texas, USA, which has suffered from severe flooding as well as on-ground and underground space constraint issues. We first applied the toolkit to create a master plan for Galena Park and evaluated the effect of the plan by using the Delft3D-FM (Flexible Mesh) flood model alongside the Long-Term Hydrologic Impact Assessment (L-THIA) model. The results demonstrate progressive reductions in stormwater runoff and NPS pollutants across different phases. These findings highlight the toolkit's effectiveness in improving water management and pollution control, providing valuable empirical evidences for similar communities facing similar challenges.

Environmental Assessment of a Unique Filtration Process for Treatment of Polluted Storm Water

Environmental Assessment of a Unique Filtration Process for Treatment of Polluted Storm Water

Determination of Pollution and Environmental Risk Assessment of Stormwater and the Receiving River, Case Study of the Sudół River Catchment, Poland

Changes in the land use of urban catchments and the discharge of stormwater to rivers are causing surface water pollution. Measurements were taken of the quality of discharged stormwater from two areas with different types of development: a residential area and a residential-commercial area, as well as the quality of the Sudół River water below the sewer outlets. The following indicators were studied: TSS, COD, N-NO3, N-NO2, TKN, TN, TP, Zn, Cu, Hg, HOI, and PAHs. The influence of land use on the magnitudes of flows in the river was modeled using the SCS-CN method and the Snyder Unit Hydrograph Model. The results showed an increase in sealing and a resulting increase in surface runoff. Concentrations of pollutants in stormwater and analysis of the potential amounts of loadings contributed by the analyzed stormwater outlets indicate that they may be responsible for the failure to meet environmental targets in the Sudół River. Environmental risk assessment shows that the aquatic ecosystem is at risk. A risk factor indicating a high risk of adverse environmental effects was determined for N-NO3, Zn, and Cu, among others.

Improving the Design and Performance of Double-Row Sediment Barriers Used During Highway Construction

Sediment barriers (SBs) are stormwater management devices often installed along the perimeter of a construction site to intercept and treat overland sediment-laden flow before discharge into the surrounding environment. Effective SB practices remove stormwater pollutants by creating a temporary impoundment upstream of the practice which facilitates sediment capture via sedimentation. Controlling agencies and design practitioners often specify the installation of two SB practices (i.e., primary and secondary SB) in areas where enhanced stormwater treatment is critical because of downstream environmental concerns (e.g., impaired waters). This study sought to identify the overall performance of a commonly specified double-row SB (i.e., double-row silt fence), as well as six alternative designs that utilized various secondary SB practices that could be easily paired with a primary silt fence SB. Small-scale experiments were conducted on each of these double-row design configurations to develop a comprehensive understanding of their performance capabilities. A statistical analysis conducted on 700 water quality data points suggests that all six alternative double-row designs significantly outperformed the double-row silt fence installation. Water quality improvements achieved using alternative secondary SBs ranged from 11% to 71% during the 30 min test period and 14% to 60% during the 90 min dewatering period. In comparison, the double-row silt fence installation only achieved 5% and 1%, respectively. Additionally, post-test observations of secondary SB cross sections indicate that, at best, only half of the matrix filter media within the secondary SB contacts sediment-laden flow. This observation suggests that alternative cross-sectional designs could improve media utilization.

Physiological Response of Two Typical Plant Species under Combined Pb and Cd Stress in Bioretention Facilities

Bioretention facilities reduce stormwater runoff and pollutants, but there is a concern that plants in bioretention facilities may absorb heavy metal pollutants from stormwater runoff, which might impair the growth of the plant species. To investigate this issue, stormwater runoff containing various amounts of Pb and Cd heavy metals was used as the irrigation water in a bioretention facility. The low concentrations of Pb and Cd were 0.08 and 0.04 mg/L, and the high values were 0.68 and 0.32 mg/L. The plant heavy metal content and physiological indicators were measured. The indicators were chlorophyll content (CC), net photosynthetic rate (NPR), and transpiration rate (TR). The results showed that the changes in plant chlorophyll content (CC) were highly correlated with changes in the plants’ Pb. Low concentrations of Pb and Cd slightly inhibited the Ginkgo biloba L. and Ligustrum × vicaryi NPRs, the effect was more obvious at high concentrations and the Ligustrum × vicaryi’s NPR decreased from the initial 8.97 μmol CO2/(m2s) to 5.77 μmol CO2/(m2s) under high concentration conditions. Pb and Cd increased the Ginkgo biloba L. and Ligustrum × vicaryi’s TRs, and the effect at low Pb and Cd concentrations was more significant. Under low concentrations of Pb and Cd stress, the Ginkgo biloba L.’s TRs reached 0.63 mmol H2O/(m2s), Ligustrum × vicaryi’s TRs reached 1.30 mmol H2O/(m2s). The TRs of the two plants in the experimental groups remained high throughout the experiment, and there was no significant inhibition. The study found that Pb and Cd in stormwater runoff did affect the physiological function of species to some extent. Different plant species behaved differently in bioretention facilities, but the stormwater runoff did not lead to the death of species. Our study may provide a better understanding of the development of typical plant species in bioretention facilities.

Effects of watershed-scale green infrastructure retrofits on urban stormwater quality: A paired watershed study to quantify nutrient and sediment removal

Urban stormwater represents a substantial source of nutrients and sediment to aquatic ecosystems. Green infrastructure (GI), including bioretention and permeable pavement, is an increasingly utilized method to treat stormwater pollutants. Using soil and plants as natural filters, these systems are effective at the site scale, but little evidence exists regarding their performance at the watershed-scale. Blueprint Columbus is an effort by the City of Columbus, Ohio, USA to retrofit GI to eliminate sanitary sewer overflows and remove 20% of total suspended solids (TSS) from existing developed areas. Changes in water quality resulting from the combined effects of many GI practices installed in 11.5 and 47.8 ha treatment watersheds were quantified using a paired-watershed approach. Based on water quality data collected by automated samplers over a 3.5-year period, significant reductions in particulate and dissolved nutrients as well as sediment were observed following the installation of GI in both treatment watersheds compared to the control. Total nitrogen (TN), phosphorus (TP), and TSS concentrations decreased by 13.7–24.1%, 20.9–47.4%, and 61.6–67.7%, respectively. Runoff attenuation by GI contributed to pollutant load reductions of 24.0–25.4% (TN), 27.8–32.6% (TP), and 59.5–78.3% (TSS). Orthophosphate concentrations and loads increased in the watershed with bioretention only but significantly decreased in the treatment watershed with bioretention and permeable pavement. Reductions in TSS concentration were similar (within a margin of 5%) to the percent of the watershed imperviousness treated by GI. Results demonstrate that GI was effective in reducing runoff event mean concentrations and loads at the watershed-scale.

Experimental Research on the Treatment of Stormwater Contaminated by Disinfectants Using Recycled Materials-Hemp Fiber and Ceramzite.

Pollution caused by the use of disinfectants in public spaces is a relatively new form of environmental contamination. During the COVID-19 pandemic of 2020-2021, early research showed a sevenfold increase in the use of disinfectants to clean outdoor spaces and a corresponding increase in environmental pollution. Typically, after entering stormwater systems, disinfectants are carried to surface waters (e.g., rivers, seas and lakes) where they react with various elements to form harmful compounds. In the absence of data, it is not possible to determine accurate levels of pollution according to the latest scientific information. Our enquiry demonstrates that stormwater pollution indicators (pH, conductivity, turbidity and color intensity) change depending on the amounts of disinfectants present. Laboratory tests were conducted using hemp fiber and ceramzite, in which filtered stormwater samples contaminated with different amounts of disinfectants showed decreases in the amounts of active chlorine from 2.93 ppm to 1.0 ppm. Changes in pH levels, conductivity, turbidity and color intensity were monitored before and after filtration; pH indicators changed slightly (from 7.81 to 7.85), turbidity changes varied in the range of 0.070-0.145 NTU and the highest value of color intensity (1.932 AV) was obtained when 50 mL of disinfectant was added to the investigated sample water. This article presents the results of our research into the impact of disinfectants on stormwater. Further investigation is needed in order to determine the impacts of chemical substances on our water ecosystem.

Investigating the influences of concave depths on stormwater runoff and pollution retention of urban grasslands.

In this study, scale-based runoff plots of concave grasslands were designed and simulated rainfall experiments were conducted to investigate their retention effectiveness for runoff volume and pollutant loads, and to analyze the influences of concave depths on runoff and pollution retention of grasslands. Results showed that mean time to runoff of concave grasslands was 88.5 minutes, which was 5.3 times than that of flat grassland. Average peak flow rate of concave grasslands was reduced by 36.2% compared with flat grassland. Concaved grasslands averagely retained 58.2% of stormwater runoff. Deeper concave depths significantly increased runoff detention and retention performance of grasslands. Total suspended solids (TSS) load reduction rates of concave grasslands were ranged from 50.8% to 97.3%. Total nitrogen (TN) load reduction rate was 49.8% for concave depth of 10 cm. Total phosphorus (TP) load reduction rates were 45.0% and 93.9% for grasslands with 5 cm and 10 cm concave depths, respectively. Pollution load reduction rates of TSS, TN and TP enhanced along with the increase in concave depths. The estimated minimum area ratios of upslope impervious surface to grasslands of 5 cm and 10 cm concave depths were approximately 1:1 under 20 mm rainfall events, and 38:1 under 5 mm rainfalls, respectively.

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.

Nitrogen transport and sources in urban stormwater with different rainfall characteristics.

Nitrogen pollution in urban stormwater has led to serious quality issues in urban water. Nitrogen pollution mitigation requires fully understanding the transport process and major nitrogen sources in urban stormwater. In this study, the concentrations and flux of various nitrogen forms during urban stormwater transport were analyzed. It was found that the concentration and flux of NO3--N and NH3-N decreased in the order of roof runoff, road runoff, and drainage runoff, while the concentration and flux of dissolved organic nitrogen (DON) and particulate nitrogen (PN) were found to be the highest in road runoff. Source quantification found that roof runoff (34%) and rainwater (34%) were the main contributors to nitrate pollution during light and moderate rains (<25 mm), while road runoff was identified as the major source (49%) of nitrate pollution during heavy rains (>25 mm) due to the large road runoff volume. Regarding particulate organic nitrogen (PON), the road runoff in commercial areas contributed most (23%) to PON pollution during light and moderate rains, while the runoff generated from pervious surfaces and drainage sediments were the primary two sources (22%) of PON during heavy rains. Moreover, the influence of rainfall characteristics on nitrate and PON source contributions was identified. The results show that antecedent dry periods were an important factor influencing nitrogen source contributions during light and moderate rains, while rainfall amount and intensity were critical factors impacting the nitrogen source contributions during heavy rains. Taking various transport processes, source contributions, and rainfall characteristics into consideration, several recommendations were given for the mitigation of nitrogen pollution in urban stormwater. This study can provide a useful perspective to understand the transport and sources of nitrogen, thus developing constructive strategies to control urban nonpoint source pollution management.

A suitable deterministic modeling approach of urban stormwater nutrient, metal and organic pollutant removal in plant biofiltration

ABSTRACT Urban water managers regard stormwater runoff and its treatment as one of the greatest challenges, due to its diffused nature and pollutant range. In response, plant biofiltration, a water-sensitive urban design technology, is increasingly preferred. However, due to varying removal performances influenced by design and operational conditions, as well as pollutant removal process complexity, it is under-utilised. This note reviews relevant pollutant removal processes and pathways; and subsequently proffers a first step summary of fundamental processes and pathways applicable to generic plant biofiltration for removal of typical stormwater pollutants. The treatment model combines relevant existing models applicable to the removal pathways of organics, NH3, NO3-, PO4 3- and metal pollutant change, as well as recommends further refinements. Advancing the understanding of plant biofilter complexity represents a significant in the urban drainage management strategy, from simple flood reduction to the recognition of the stochastic nature of interactions influencing water quality.

Willingness to pay for ecosystem benefits of green stormwater infrastructure in Chinese sponge cities

Globally, green stormwater infrastructure (GSI) has been adopted to address urban flash flooding and stormwater pollution and provide additional ecosystem benefits such as recreation, education, and aesthetics to urban communities. However, there has been a lack of research on people's preferences for different ecosystem benefits, making it challenging to understand synergies and trade-offs among co-benefits and optimize GSI planning and design. Additionally, urban stormwater management programs commonly face long-term financial challenges, demanding research that investigates the feasibility of public utility programs. This study fills these gaps in a Chinese context by employing a discrete choice experiment (DCE) to compare public preferences and estimate the monetary values of four GSI benefits, including stormwater quantity and quality treatment, educational benefit, aesthetics, and recreational benefits, in four small-to-medium pilot sponge cities. Results show that respondents preferred some kinds of GSI programs to a conventional lawn space in their living environments, and they had significant willingness to pay (WTP) for GSI programs to obtain educational ($14.8 per household per year, p < 0.001) and recreational benefits ($10.8 per household per year, p < 0.001). Stormwater treatment, as the environmental benefit prioritized by governmental agencies, however, did not generate a significant willingness to pay in any studied cities. Residents also showed indifference towards three different planting aesthetic styles (i.e., formal vs. mixed vs. naturalistic). We conclude that providing social-oriented benefits such as education and recreation is more likely to garner urban residents' financial support for GSI development in the chosen sponge cities. While stormwater utility can be a viable funding source to supplement urban stormwater management programs, people's WTP remains limited, and other financial mechanisms need to be explored.

An Assessment of Groundwater Development Using Pervious Concrete-A Case Study in JSSATE Campus Bangalore

Pervious concrete is a special kind of concrete with a high porosity that is used for concrete flatwork applications to lessen runoff from a site and facilitate groundwater recharging. Water from precipitation and other sources can directly pass through pervious concrete. Other names for it include porous pavement, permeable concrete, no-fines concrete, and porous concrete. Pervious concrete is made with large particles and minimal to no tiny Aggregates. The concrete paste then coats the aggregates and allows water to pass through the concrete slab. In order to reduce runoff from a site and enable groundwater recharge, pervious concrete is a specific variety of concrete with a high porosity that is used for concrete flatwork applications. Pervious concrete allows water from precipitation and other sources to pass through directly. Porous concrete, permeable concrete, no-fine concrete, and porous pavement are other names for it. Pervious concrete is made with large aggregates with little or no small aggregates. The Environmental Protection Agency (EPA) regards pervious concrete as a means of providing storm water management, pollution reduction, and appropriate development. The development of trees is also enhanced by pervious concrete. The behaviour of pervious concrete has been experimentally explored in the current work. The ratio of water to cement was 0.45. The ratio of coarse aggregate to cement was maintained at varying ratios of 1:4 and 1:6. Half of cement is made of fly ash. Experimental research has been done on a variety of pervious concrete qualities, such as workability and compressive strength tests after 7 and 14 days

Influence of particle size on diffuse particulate pollutants in combined sewer systems

Since combined sewer systems are still considered as a threat to urban water environment, understand their pollution transport process and load distribution characteristics during rainfall-runoff events would assist to mitigate urban stormwater pollution. In this study, built-up and wash-off processes of particulate pollutants on road surface and in sewer were synchronously observed during eight natural rainfall events in the combined sewer system in Zhuhai, Southern China. Field observation results showed the significant influence of particles size distribution characteristics on TSS concentration. High TSS concentrations (Road runoff, >200 mg/L; combined sewer runoff, >150 mg/L) usually contained relatively coarse particles (>100 μm) during the eight rainfall events, but the counter argument. Combined sewer runoff had a particle size coarser than road runoff. The relationship between the event means concentration (EMC) of TSS from road and combined sewer runoff varied with rainfall. EMC of TSS in road runoff were higher than that in sewer runoff during small rainfall, while that in combined sewer runoff were higher during large rainfall. The results also showed that 65.2 % of total nitrogen (TN) loadings and 62.3 % of total phosphorous (TP) loadings in the catchment came from combined sewer sediments, while 58.6 % of chemical oxygen demand (COD) loadings came from road runoff, which were mainly determined by the content of each pollutant in the sewer sediments and road-deposited sediments (RDS). Additionally, high pollutant loads phases (drainage of pollutant loads faster than runoff at a given incremental time during an event) of road runoff occurred earlier than that of combined sewer runoff. These findings can provide a basis for the type selection and scale determination of stormwater control measures in combined sewer systems.

Field Application of Spent Lime Water Treatment Residual for the Removal of Phosphorus and other Pollutants in Urban Stormwater Runoff

The threat of anthropogenic eutrophication and harmful algal blooms in lakes requires the development of innovative stormwater best management practices (BMPs) to reduce the external loading of phosphorus (P). This paper presents the findings of a 5-year study of a full-scale P removal structure constructed in Minnesota, USA with spent lime drinking water treatment residual (DWTR), a by-product of water softening at a local water treatment plant. Influent and effluent water samples were collected by auto-samplers during 43 storm events during the growing season. Samples were analyzed for P constituents, heavy metals, total suspended solids (TSS), and pH. Toxicity of the effluent was assessed using Ceriodaphnia dubia. Flow-weighted removal effectiveness was calculated for each storm event. Overall, the spent lime DWTR reduced total P loading by 70.9%, dissolved reactive P by 78.5%, dissolved P by 74.7%, and TSS by 58.5%. A significant reduction in heavy metals was also observed. Toxicity tests indicated the aquatic toxicity of the effluent treated with spent lime DWTR was not different from untreated stormwater. This study provided long-term real-world data that demonstrated that a full-scale P removal structure with spent lime DWTR significantly reduced P and other pollutants in stormwater discharging to an urban lake. Therefore, spent lime DWTR, which is currently treated as a waste product, is a promising filter material for stormwater treatment.

Alfalfa biochar supported Mg-Fe layered double hydroxide as filter media to remove trace metal(loid)s from stormwater

Polluted stormwater (PSW) treatment is becoming increasingly important because of the existence of multiple pollutants from non-point pollution sources. Alfalfa biochar loaded with Mg/Fe layered double hydroxide (AF-LDH) was successfully synthesized to remove trace metal(loid)s from stormwater. The adsorption kinetics and isotherms of metal(loid)s in a mono-component system and the reusability of the composite materials was investigated in this study. The result showed that the maximum removal efficiency for Pb(II), Cu(II), Zn(II), Cd(II), As(V), and Cr(VI) were 98.98 %, 98.11 %, 97.88 %, 97.71 %, 98.81 %, and 50.89 %, respectively, when added calcined AF-LDH (AF-LDO) composite material to the multi-component solution. The AF-LDH and AF-LDO could efficiently remove trace pollutants (10‐100 μg/L) from multi-component solution, especially for AF-LDO, which could completely remove the tested six trace metal(loid)s. Furthermore, Fourier transform infrared spectra and X-ray diffraction characterizations supported the Mg/Fe layered double hydroxide reconstruction. The main mechanisms of Pb(II), Cu(II), Zn(II), and Cd(II) (cationic metals) removal were ion exchange and surface precipitation, whereas As(V) and Cr(VI) (anionic metals) were mainly dislodged through the formation of surface complexation, electrostatic attraction, and interlayer anion exchange, concerning the –OH and –COOH of AF-LDH. Importantly, the results of the column experiment demonstrated that AF-LDO was superior to AF-LDH for anionic metal removal from stormwater. In this study, we synthesized AF-LDH and AF-LDO for trace metal(loid) removal and proposed a new and practical approach for stormwater purification.

A Review of Pollutant Concentrations in Urban Stormwater Across Eastern Australia, After 20 Years

Concerns about pollutants in urban stormwater were initially raised in the early 1970s. Australian investigations decades later, also found urban stormwater runoff contained elevated levels of sediment and nutrients, as well as heavy metals, that brought stormwater management to the forefront for regulators. Planning policies were implemented to integrate stormwater management into development in the form of water sensitive urban design (WSUD), also known internationally as low-impact design (LID) and Sustainable Urban Design solutions (SUDs). Since their introduction, comprehensive broad scale field research to verify their success in achieving load reduction targets (LRTs), has been limited. Paucity of field data on the performance of WSUD has prompted organisations to initiate their own locally-specific studies. Limited regulatory guidance on design of monitoring programs has resulted in various methodologies and meta-data recording. This research review collates urban stormwater data from 77 Australian studies, from geographic regions of east coast Australia. The raw dataset in this review included 2,836 events and 4,536 individual results, collected between 1993 and 2021 from local councils, research organisations and water authorities. The review examined total suspended solids (TSS), total phosphorus (TP) and total nitrogen (TN) concentrations, prior to any form of treatment measures as they are the focus of current guidelines and standards for stormwater management. Seminal research, used to inform stormwater guidelines and water quality modelling across Australia, is significantly different (p &amp;lt; 0.001), in this case approximately double the reviewed concentrations. International data is also &amp;gt;20% higher, on average. Geographic location of catchments had the greatest influence on pollutant concentrations, after accounting for the effects of land use and catchment urbanisation date (p &amp;lt; 0.001). Based on the findings of this review, generic load reduction targets (expressed as a percentage of annual inputs, e.g. 80% TSS reduction, 45% TN, 45% TP) typical in current Australian planning regulations, may be sub-optimal in achieving receiving water quality goals, particularly given the difficulty of removing pollutants when present in low concentrations. Alternately, place-based discharge targets which meet, or exceed, background water quality, or ecological and hydrological benchmarks may be a more appropriate tool to achieve environmental objectives.

Assessment of pyrene adsorption on biochars prepared from green infrastructure plants: Toward a closed-loop recycling in managing toxic stormwater pollutants

Recently biochar is receiving increased attention as an alternative filter medium for enhanced stormwater management. This study attempted to recycle plants harvested from the upper green infrastructure (GI) component for reuse in the lower GI component as a filter medium. Dawn redwood (DR) and bridal wreath (BW) were harvested and converted to biochar. Leaves and branches of each plant species were pyrolyzed at 300 and 500 °C and the prepared biochars were characterized and evaluated for their adsorption capacity of pyrene, one of the major polycyclic aromatic hydrocarbons (PAHs) in urban stormwater runoff. The biochar made from DR leaf at 300 °C showed the highest pyrene adsorption efficiency and was well-fitted with pseudo-second order kinetics and Freundlich isotherm. The first biochar regeneration cycle demonstrated that both thermal and solvent extraction showed high pyrene adsorption efficiency recovery with values of 98.8 and 98.0%, respectively. The relationships between surface properties and adsorption capacities of biochar for PAHs and heavy metals, the two major toxic stormwater pollutants, were further investigated using data pooled from the existing studies. The literature data analysis showed that biochars produced at a lower pyrolysis temperature (~300 °C) can efficiently remove PAHs and heavy metals due to higher hydrophobic interactions and higher cationic exchange capacity, respectively. This study suggests the potential feasibility of closed-loop recycling of GI plants for sustainable stormwater treatment and carbon sequestration.