Bioretention Cells Research Articles

Effect of low-impact development practices on the treatment of urban runoff

The impact of a bioretention cell on the urban runoff (ur) quality was evaluated. The cell was constructed with the following stratification of materials (from the base): 20% coarse gravel, 40% gravel, hydrogel, 40% clinoptilolite, and succulent plants as cover. It was fed with real UR for 24 hours at constant speed to simulate 3.9 mm of precipitation. Samples were taken at the inlet and outlet of the cell, which were analyzed in terms of COD, N-NH4+, N-NO2-, N-NO3-, PO43- (total and dissolved), Escherichia coli density and various metals (Al, Fe, Cu, Mn, Pb, Zn, Cr, Cd and Ni) according to standard methods. To assess the effect of the cell on water quality, we proposed an index that we calculated for the aeu before and after receiving the treatment. The system removed several of the pollutants evaluated: COD (28.5%), N-NH4+ (84.3%), N-NO3- (49.4%), total PO43- (94.8%), and dissolved PO43- (86.2%). The metals were removed with efficiencies between 90 and 99%, with the exception of Ni (58.7%), while E. coli was completely removed. The index calculated for the water treated in the cell was considerably lower than the index calculated for the inlet aeu, which shows the bioretention effect on water quality. 

A Tool for Water Balance Analysis of Bioretention Cells

AbstractBioretention has become one of the most popular urban stormwater best management practices. An easy-to-use analytical tool is developed here to investigate the water balance dynamics of bio...

Influence of low-phosphorus compost and vegetation in bioretention for nutrient and sediment control in runoff from a dairy farm production area

We evaluated the effects of a low-phosphorus compost and vegetation (Panicum virgatum) on the ability of three bioretention cells to remove nutrients and total suspended solids (TSS) from storm runoff originating in a dairy farm production area. The three experimental treatments included a bioretention cell without compost or vegetation (CV), a cell with no compost but vegetation (C-V+), and a cell with vegetation and compost (C + V+); the experimental design allowed for isolation of the variables' (i.e., compost and vegetation) effects on pollutant concentration and mass removal. Influent and effluent were monitored for dissolved and total phosphorus (P) and nitrogen (N), and TSS throughout the first growing season post installation. All bioretention cells significantly reduced pollutant concentrations and loads of TSS, total and dissolved P, and NH4+ in the effluent, but significantly exported NOx− to the effluent. All cells reduced total N (TN) concentrations, with significant reduction observed only in the C-V+ cell, which was the only treatment that retained TN load. Compost treatment significantly increased P. virgatum biomass, but not survival during the first year. P. virgatum coverage in compost and no-compost treatments were similar the second year. While low-P compost is still preferable to other composts higher in P content, we cannot conclude that any compost is necessary in the soil media for plant establishment. Due to anticipated nutrients inputs in a setting like this dairy operation site, omitting compost and avoiding nutrient leaching while waiting for plants to grow should be considered for better nutrient removal performance, even if plants may take more time to establish.

Assessing the impact of spatial allocation of bioretention cells on shallow groundwater – An integrated surface-subsurface catchment-scale analysis with SWMM-MODFLOW

Well-designed and implemented green infrastructure (GI) can help to recover the natural hydrologic regime of urban areas. A large-scale GI planning requires a good understanding of the impact of GI spatial allocation on surface-subsurface hydrologic dynamics. This study, firstly, developed a coupled surface-subsurface hydrological model (SWMM-MODFLOW) that can simulate fine-temporal-scale two-way interactions between GI and groundwater at catchment scale. The model was calibrated and validated using the monitoring data at one urban catchment within Kitsap County, WA, US. Based on the validated model, a series of hypothetical simulations was then performed to evaluate how spatial allocation of bioretention cells (BCs), one type of GI, influences and correlates with surface runoff and groundwater table dynamics. The spatial allocation was represented by implementation ratio (i.e., area), aggregation level (i.e., density) and location of BCs. The hydrologic dynamics were quantified by peak and volume reductions of surface runoff, as well as groundwater table rise and standard deviation of groundwater levels. A small number of BCs can raise groundwater table locally and regionally. However, it may not affect the spatial uniformity of groundwater levels (represented as the standard deviation of groundwater levels) if being properly allocated. Although the impact of aggregation level of BCs was relatively low compared to the implementation ratio and relative location of BCs, more-distributed BCs resulted in lower peak groundwater table rises but higher temporally-averaged groundwater table rises. Allocating BCs upstream resulted in higher groundwater table rises regionally, which is recommended for areas of deeper groundwater tables. While, allocating BCs downstream is more recommended for areas of shallower groundwater tables. BCs of greater surface runoff control efficiencies lead to higher groundwater table rises, which highlights the importance of considering the tradeoff between surface runoff control and groundwater protection in GI planning.

Carbon-to-nitrogen ratio influence on the performance of bioretention for wastewater treatment.

Bioretention cell (BRC), bioretention cell with microbial fuel cell (BRC-MFC), and an enhanced combined BRC-MFC system with bimetallic zero-valent iron (BRC-MFC-BZVI) were implemented in current study to treat the domestic wastewater. Nitrogen removal characteristics of three systems were investigated by adjusting influent carbon/nitrogen ratio (C/N ratio of 2.54-19.36). Results revealed that the nitrification and denitrification performances were mainly influenced by organic matter and system combination, which further affected nitrogen removal. When the influent C/N ratio was between 2 to 3, compared with BRC system, in BRC-MFC and BRC-MFC-BZVI system, chemical oxygen demand (COD), total nitrogen (TN), and ammonical nitrogen (NH4+-N) removal efficiencies were still reached to 83.04%, 61.06%, and 42.26% and 86.53%, 43.61%, and 50.99% respectively, which simultaneously achieved high-efficiency of organic matter and nitrogen removal. The efficient supply of electrons in the BRC-MFC and BRC-MFC-BZVI processes was the main reason to achieve profound denitrification removal under the condition of low C/N. Removal rates of nitrate (NO3--N) and nitrite (NO2--N) were relatively higher due to microbial-driven redox reactions caused by driving electrons to flow in the closed circuit of metal wire connection. Moreover, phylogenetic diversity of bacterial communities mainly induced the catalytic iron, which further enhanced biological nitrogen reduction. The maximum efficient removal of organic matter (OM), TN, and NH4 + -N were obtained in the BRC-MFC-BZVI system, which were 98.42% (C/N = 10.42), 55.61% (C/N = 4.16), and 61.13% (C/N = 4.16), respectively.

Integrating blue-green and grey infrastructure through an adaptation pathways approach to surface water flooding.

A range of solutions to future flood risk are available ranging from blue-green infrastructure (BGI) as commonly incorporated in sustainable drainage systems (SuDS) to traditional grey infrastructure (e.g. pipe networks, storage tanks, flood walls). Each offers a different profile with respect to costs, flexibility of implementation and the ability to deliver a range of wider benefits beyond their flood protection function. An important question that must be addressed when considering these approaches is what is the most suitable mix of grey and blue-green solutions to urban flooding at any location and at any future time? This paper uses an adaptation pathways approach to compare a range of alternative options to deal with current and expected future flood risk in part of a London borough. Solutions considered separately and in combination include grey pipe expansion, bioretention cells, permeable pavements and storage ponds. A methodological framework combines a range of existing tools to develop, assess and characterize each pathway, including a storm water management model (SWMM), a SuDs opportunity selection tool, an adaptation pathway generator and the CIRIA B£ST tool for monetizing multiple benefits. Climate change is represented by the UK Water Industry Research method for establishing future rainfall intensities for sewer and BGI design. The results showed that by extending the way in which adaptation pathways are compared and evaluated through the wider consideration of multiple benefits there is a trade-off between deferring interventions until they are needed for flood risk mitigation and delivering the multiple benefits associated with interventions so that performance thresholds do not need to be met before introducing new options. The relative contribution of each option's capital and operation and maintenance costs has implications on when the option is implemented as well as the rate of implementation. The monetization of the multiple benefits associated with each pathway shows that their economic co-evaluation alongside infrastructure costs can change the preference for one pathway over another. This article is part of the theme issue 'Urban flood resilience'.

Optimizing the cost-effectiveness of low impact development (LID) practices using an analytical probabilistic approach

ABSTRACTTo select optimal LID in urban areas, an optimization assessment framework considering hydrological processes and cost-effectiveness is proposed. To provide the desired runoff reduction efficiencies, hydrological processes of LID were analyzed using a probabilistic analysis of rainfall event characteristics. Meanwhile, life-cycle costs were estimated to determine benefits and costs of implementing different LID units. Finally, various solutions having maximum runoff reductions but different costs were selected using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The results show that the bioretention cell, which had maximum runoff reduction capacity, was identified as a priority measure for implementation. However, given the potential for large implementation areas, resulting in marked runoff reduction benefits, permeable pavements are a more reasonable measure for the study area. Using the NSGA-II to identify optimal cost-effective LID options is convenient for decision makers, tasked with selecting solutions based on their available budgets and runoff reduction objectives in urban environments.

Modeling and Design Scenario Analysis of Long-Term Monitored Bioretention System for Rainfall-Runoff Reduction to Combined Sewer in Cincinnati, OH.

Green infrastructure (GI) is a contemporary approach to the management of stormwater and limits its intrusion into wastewater collection systems. GI practices, such as bioretention systems, affect the local water cycle by encouraging detention, infiltration, and evapotranspiration of intercepted runoff. They may also affect water quality by either contributing nutrients to stormwater or removing pollutants through filtration or biogeochemical transformation. Therefore, for a complete understanding of GI effects, a thorough water-cycle monitoring and simulation approach is needed. In this study, the Green Infrastructure Flexible Model (GIFMod) was used to simulate hydraulic and water quality processes in a system of two bioretention cells, built in series, that drain a small catchment (3.41 ac). The goal was to evaluate the long-term effectiveness of the system at reducing hydrologic and nutrient loads to a combined sewer system. The calibrated model was used to determine cumulative load reductions afforded by the GI system over a 3-year simulation and to evaluate different design scenarios on the performance of the bioretention systems. The results show that hydraulic retention time (HRT) mainly regulates the effectiveness of the bioretention system for flow reduction. The bioretention systems at their current design reduced approximately 50% of the runoff volume before discharging into the sewer system. The engineered soil of the bioretention was found to be a net source of nitrate in the effluent. The results of the multiple design scenarios indicated that adding a riser-type outlet and increasing the storage volume of the aggregate layer of the bioretention system would result in moderate improvements in reduction efficiency, while increasing the catchment area would significantly reduce its effectiveness. Of these modifications, adding a riser feature constitutes a cost-effective design feature that in this case was easily implemented post construction and, therefore, is recommended for similar bioretention installations.

Enhanced bioretention cell modeling with DRAINMOD-Urban: Moving from water balances to hydrograph production

Bioretention systems have become a leading stormwater control measure for mitigating urban hydrology. Although these systems have performed well in many site-scale field studies, less investigation has been directed toward effectively modeling these systems. This is critical, as modeling of bioretention systems provides an avenue for evaluating their effectiveness prior to devoting time and resources into installation. Many hydrologic models capable of simulating bioretention consist of lumped parameters and simplifications that do not fully account for fundamental hydrologic processes such as soil-water interactions. DRAINMOD has shown promise for obtaining detailed daily water balances within bioretention systems under continuous simulations. One significant advantage of DRAINMOD is that it uses the soil-water characteristic curve to account for fluctuations in soil moisture instead of assuming saturation; however, the model historically only produces daily outputs. For this study, DRAINMOD was modified to develop DRAINMOD-Urban, which allows high temporal resolution inputs and outputs, more closely matching the residence time of runoff in urban systems. DRAINMOD-Urban simulations of a bioretention cell in Ohio, USA, revealed that DRAINMOD-Urban could effectively produce hydrographs with a cumulative Nash-Sutcliffe Efficiency (NSE) of 0.60 for the 12 events that produced drainage over a 7-month monitoring period. Overflow was also modeled by DRAINMOD-Urban, but additional overflow data are necessary to derive conclusions about model effectiveness in predicting this hydrologic component. Input parameters previously calibrated for the DRAINMOD model did not translate well to DRAINMOD-Urban with the top-down approach applied in this study (NSE = 0.31 for drainage and NSE = −1.83 for overflow), but the bottom-up approach showed that parameters calibrated with DRAINMOD-Urban (NSE = 0.60 for drainage and NSE = −0.1 for overflow) could be used in DRAINMOD to obtain reasonable drainage volumes (25.6% error compared to measured values). This study suggests DRAINMOD-Urban is an effective tool for modeling bioretention hydrographs and demonstrates the importance of temporal scale in bioretention modeling by illustrating multiple model calibration approaches. Despite the promising results of this study, additional studies are recommended where validation of the model is performed at more sites, in particular for events with overflow. Further, sensitivity analysis of input parameters and comparison of DRAINMOD-Urban to other commonly used bioretention models would inform future modeling efforts.

Microbial diversity for the improvement of nitrogen removal in stormwater bioretention cells with three aquatic plants.

The aquatic plants Iris pseudacorus L., Canna indica L. and Lythrum salicaria L. have been proved to be potential choices for nitrogen removal. However, little is known about microbial diversity for the improvement of nitrogen removal (nitrification and denitrification) in stormwater bioretention cells with the above plants. In this study, batch experiments were conducted to investigate nitrogen removal, substrate layer status, and bacterial community structure to understand microbial diversity and evaluate its effects on performances of nitrogen removal. Ammonia nitrogen removal in the bioretention cell with Lythrum salicaria L. was the highest (88.1%), which was consistent with oxidation reduction potential (ORP) in the bioretention cells. Whilst, removals for both total nitrogen and nitrate were the highest in the bioretention cell with Canna indica L., which was in line with urease activity in the mentioned cells. The used plants had different impact on top 11 dominant microflora at phylum level in the used bioretention cells. Ramlibacter and Nitrosomonadaceaea were both responsible for the difference of nitrogen removal in the bioretention cells with three aquatic plants, suggesting the enhancement of the above dominant microflora could strengthen nitrogen removal in the used bioretention cells.

Design and operation of submerged layer in bioretention for enhanced nitrate removal

Abstract Bioretention, initially designed for treating discontinuous runoff pollution, faces considerable challenges in its trade-off between the hydraulic retention time (HRT) and its treatment capacity. In this study, six enhanced submerged media together with four HRTs were designed for bioretention cells to treat the highly nitrogenous river water in Tai lake basin in Yangtze River delta, China. Results revealed that bioretention with activated carbon has the highest removal of nitrate (NO3−-N) (93–96%) compared with surfactant-modified activated carbon (SMAC), surfactant-modified zeolite (SMZ), zeolite, fly ash and ceramsite. Although the SMAC had the best absorption for NO3−-N and could desorb NO3−-N when its concentration was low in the submerged layer, the desorbed surfactant could inhibit the growth of denitrifying bacteria, which leads to low removal efficiency (49–66%). The dynamic balancing of NO3−-N desorption and denitrifying system restrain in the SMAC device was observed and explained. The best activated carbon-gravel proportion in the submerged layer was 1:1 (150 mm). Such design could ensure the stable and efficient NO3−-N removal rate (93–94%) under high inflow concentration (28.9 mg/L) and high hydraulic loading (8.2 cm/h).

Nitrogen removal performance of microbial fuel cell enhanced bioretention system

Abstract Bioretention cell (BRC) and an enhanced system combining bioretention cell with microbial fuel cell (BRC-MFC) were used to treat domestic wastewater. Nitrogen removal characteristics and permeation characteristics of two systems were investigated by adjusting influent carbon/nitrogen ratio (C/N = 2–20). Results showed that nitrification and denitrification performances were mainly influenced by organic matter and system combination, which further effected the nitrogen removal. When optimal operating parameters were: electrode space of 30 cm, hydraulic load of 1.0 m3/(m2·d) and inlet/reaction time of 1/8 in BRC-MFC system, chemical oxygen demand (COD), total nitrogen (TN) and NH4+ removal efficiencies still reached 97.63, 64, and 42.26%, respectively and achieved high removal efficiency of organic matter and nitrogen simultaneously compared to the BRC system. Efficient supply of electron and phylogenetic diversity of bacterial communities in BRC-MFC process was the main reason to achieve deep denitrification removal. After the V3-V4 variable region of 16S rRNA gene was sequenced by the Miseq high-throughput sequencing method, introduction of MFC enhancement technology affected the microbial community structure in the system. The presence of MFC contributed to an increase in community diversity (from 14 to 19 phyla). The results provide a simple method without kinetic energy for simultaneous denitrification and steady infiltration of bioretention.

Bioretention cell age and construction style influence stormwater pollutant dynamics

In urbanized landscapes, green infrastructure is proposed as a method for using relatively small plots of land to manage stormwater and protect receiving ecosystems from pollutants. Bioretention cells can infiltrate stormwater from roads and parking lots, and as stormwater passed through the soils, metals can be removed. Metal removal and storage has been demonstrated in laboratory media columns and field-scale test cells, but we have an incomplete understanding of metal removal and accumulation in aging bioretention cells in the field. We surveyed 25 bioretention cells (0–7 years of service) for soil physicochemistry to determine which characteristics related to soil metal (Cu, Pb, and Zn) concentrations. We collected soil cores and treated them with simulated stormwater to measure potential rates of metal removal under different metal and salt concentrations. Older bioretention cells had higher Cu, Pb, and Zn concentrations in soil, which indicates accumulation and storage over time. The oldest cells had metal concentrations that were not a risk to human health but which approached screening thresholds for potential impairment of plants. Soil organic matter content (OM) was positively associated with metal concentrations which highlights the importance of OM in the functioning of cells. Retrofit bioretention cells were younger with less OM and more clay than cells built concurrently with new parking lot construction (i.e., de novo), but after 2.7 years of service, soil OM was similar between retrofit and de novo builds. Soil cores from de novo bioretention cells retained more stormwater metals than soil cores from retrofit cells, and this was likely due to differences in soil OM. Elevated road salt in stormwater was associated with less effective metal removal and leaching of Zn from soils. Overall, these data suggest that management (e.g., salting) and design (e.g., construction) decisions can greatly influence metal removal function of bioretention cells.

Simulating the effects of low impact development approaches on urban flooding: a case study from Tehran, Iran.

Low impact development (LID) methods have been shown to be efficient in reducing the peak flow and total volume of urban stormwater, which is a top priority for effective urban stormwater management in many municipalities. However, decision-makers need information on the effects of LIDs and their associated costs before allocating limited resources. In this study, the Storm Water Management Model (SWMM) was used to investigate the effects of five different LID scenarios on urban flooding in a district in Tehran, Iran. The LID scenarios included rain barrel (RB) at two sizes, bio-retention cell (BRC), and combinations of the two structures. The results showed that significant node flooding and overflow volume would occur in the study area under the existing conditions, especially for rainfall events with longer return periods. BRC and combinations of BRC and RBs were the most effective options in reducing flooding, while the smaller-size RB was the cheapest alternative. However, normalized cost, obtained through dividing the total cost by the percent reduction in node flooding and/or overflow volume, was smallest for BRC. The results of this study demonstrate how hydraulic modeling can be combined with economic analysis to identify the most efficient and affordable LID practices for urban areas.

Influence of land use and land cover’s change on the hydrological regime at a Brazilian southeast urbanized watershed

Land use and land cover have a direct influence on the hydrological regime. Urbanization and deforestation are accountable for reducing the water infiltration and consequent runoff’s increase. These modifications lead to high peak flows responsible for catastrophic events. Thus, this work analyzed the impact of land use and land cover’s change on the hydrological regime in a Brazilian southeastern urbanized watershed; considering current and future scenarios. The hydrological model HEC–HMS was used to estimate stream flow and aided in the search for suitable solutions. Using the Land Change Modeler tool made possible to design 2030’s land use and land cover in Grande river watershed. Hydrological simulations were carried out for 2030 using HEC–HMS. Some of the forested areas were replaced by agriculture and pasture. The agricultural areas were the ones that showed greater expansion. Such changes contributed to a mean increase of 52% in the stream flow hydrograph when compared to the watershed’s current scenario. After the use of best management practices, the stream flow hydrograph had a mean reduction of 44%. The structures considered were bio-retention cells, rain gardens, infiltration trenches, and permeable pavements for urban areas. For rural areas, the practices suggested were level terraces, no-till farming, and contour farming. All structures were applied in a distributed manner throughout the watershed. Therefore, it is concluded that land use and land cover’s change in Grande river watershed significantly influence the stream flow regime, and the use of best management practices proved efficient in reducing floods.

An Integrated Fuzzy Simulation-Optimization Model for Supporting Low Impact Development Design under Uncertainty

Seeking cost-effective design of urban hydrological facilities and drainage systems is an important task for many city planners. However, such a process has always been complicated with intrinsic uncertainties. This work presented an integrated fuzzy simulation-optimization model (FSOM) for supporting Low Impact Development (LID) design under model uncertainties. Various LID implementation schemes involving green roof, bio-retention cell, and permeable pavement were simulated through an urban hydrological model. Three model parameters were assumed as fuzzy sets. In a case study, fuzzy simulation (FS) and genetic algorithm (GA) were employed to search the optimal schemes of LIDs under various confidence levels of satisfying flood control constraints. Comparison of FSOM to traditional deterministic and stochastic models were also carried out. It was shown that FSOM could offer a flexible way of defining and assessing uncertainties associated with hydrological modeling and generate solutions that were comparable to those from either deterministic or stochastic models. However, FSOM also showed limitation of high computational requirement.

Bioretention cell incorporating Fe-biochar and saturated zones for enhanced stormwater runoff treatment

Nitrogen (N) and phosphorus (P) removal in conventional bioretention systems is highly variable. Therefore, five novel experimental columns with different media configurations and constituents, and incorporating a saturated zone were developed and assessed to optimize the removal of N, P and other nutrients. Three types of media composed of the conventional mixed sand and soil media (T1), biochar-amended media (T2), and iron-coated biochar (ICB)-amended media (T3) were evaluated. Two of the experimental columns were designed with double-layer configurations, while the other three were of a single-layer structure. Removal efficiencies of nutrients in the experimental columns were evaluated and compared using simulated runoff. Also, the effect of media depth on the retention of P and denitrifying enzyme activity (DEA) in the bioretention columns were evaluated. The experimental column only filled with T3 showed the best performance for COD, ammonia (NH4+-N) and total phosphorus (TP) removal (94.6%, 98.3% and 93.70%, respectively), whereas columns filled with T2 performed poorly for TP removal (57.36%). For the removal of nitrate (NO3−-N) and total nitrogen (TN), the columns using a single-layer and only filled with either T3 or T2 exhibited the best performance (93% and 97% TN removal, respectively). Overall, this study demonstrates that our proposed single-layered bioretention cell only filled with T3 and incorporating a saturated zone effectively improves the runoff quality, and can provide a new bioretention cell configuration for efficient stormwater treatment.

Impacts of rainfall and catchment characteristics on bioretention cell performance

Although many studies have evaluated the impacts of bioretention cell (BRC) design elements on hydrologic performance, few have investigated the roles played by site characteristics and rainfall patterns. The objectives of this study were to assess the impacts of rainfall and catchments with different characteristics on the hydrologic performance of BRCs and identify important factors in sizing bioretention when hydrologic performance was oriented for the design using a modeling approach. A 10-year record of rainfall data was used to identify the frequency and magnitude of rainfall events. The results showed that although the small and medium rainfall events were dominant they contributed less to the total rainfall depth than the large rainfall events. The ratio of runoff coefficient to imperviousness can be used as an indicator to explain why BRCs perform differently with the same design strategy under the same rainfall events. Rainfall patterns had significant impacts on the hydrologic performance of BRCs by influencing the overflow and underdrain flow. BRCs performed better for rainfall events with a longer duration and lower rainfall intensity because they generated smoother runoff processes into the BRCs. On the basis of these results, the runoff coefficient is suggested for BRC surface design.

Performance evaluation of modified bioretention systems with alkaline solid wastes for enhanced nutrient removal from stormwater runoff

Bioretention systems have been found to be potential candidates for the removal of various pollutants/nutrients from rainfall or stormwater runoff. Despite bioretention has been widely developed for the removal of nutrients from stormwater, effective removal of both phosphorus and nitrogen is still a challenge. Hence, in this study, bioretention systems modified by alkaline solid waste media have been reported for the effective removal of nutrients. Six different types of solid wastes were first assessed using leaching and adsorption tests, and then the bottom ash from a refuse incineration plant was selected as a modifier. The bottom ash was mixed with soil to form a special media as the filter layer in the bioretention systems. The nutrient removal efficiencies of the modified bioretention systems were evaluated and also compared with those of the unmodified control. For this purpose, the design of the modified filter media with a saturated zone was combined to enhance the simultaneous removal of nitrogen and phosphorus. The effect of different rainfall intensities and nutrient concentrations in stormwater runoff on the removal efficiency of nutrients was evaluated. The results indicated that the modified bioretention with bottom ash modified soil media and saturated zone could exhibit the excellent removal efficiency of nitrogen and phosphorus from stormwater runoff. The extent of removal of total nitrogen, total Kjeldahl nitrogen, and total phosphorus was found to be 58–70%, 66–82% and 82–97%, respectively. The performed correlation analysis showed that the bioretention cell using the special media could simultaneously enhance the removal of phosphorus and nitrogen. As a part of this study, the adsorption isotherms of phosphorus removal by the modified bioretention systems have also been determined. Finally, the implications and opportunities for deploying modified bioretention systems for optimizing water-energy nexus and stormwater management were illustrated. In overall, this study demonstrated that the modified bioretention systems could substantially enhance the removal efficiencies of nutrients from stormwater runoff.

Using spatially-identified effective impervious area to target green infrastructure retrofits: A modeling study in Knoxville, TN

There is a need for enhanced guidance in siting distributed, infiltrative green infrastructure (GI) practices, especially in densely developed urban watersheds where retrofits come at a high cost. To maximize the hydrologic benefit of GI practices on urban streams, the disconnection of effective impervious areas (EIA), or those impervious areas hydraulically connected to the stormwater network, has been identified as a strategic management approach that is expected to have the greatest impact. The overall effect of full disconnection of spatially-identified EIA on watershed hydrology is uncertain because this type of full disconnection is rarely brought to full-scale implementation. In this study, spatial EIA identification is used to parametrize an urban runoff model using the United States Environmental Protection Agency’s Storm Water Management Model (SWMM). The calibrated model is used to assess runoff reductions resulting from GI practices distributed through the watershed via different placement strategies, both spatially-informed and not. Full treatment of the spatially-identified EIA using bioretention cells was compared to two scenarios treating the same area of impervious surfaces, but with random placement either among all impervious areas or placement focused in areas of higher imperviousness. Model results indicate that substantially higher runoff reduction could be realized by targeting EIA, with a median runoff reduction of nearly 30% more than other treatment scenarios across storm events ranging from 1.27 to 20.7 mm using this strategic siting. Further improvements in optimizing distributed infiltrative GI practice placement are needed and targeting of spatially-identified EIA appears to be a viable method for increasing the hydrologic improvements realized through watershed scale implementations.