Occurrence, Concentration, and Distribution of 35 PFASs and Their Precursors Retained in 20 Stormwater Biofilters.

Current knowledge about the fate and transport behaviors of per- and polyfluoroalkyl substances (PFASs) in urban stormwater biofilter facilities is very limited. C5-14,16 perfluoroalkyl carboxylic acids [perfluorinated carboxylic acids (PFCAs)], C4,8,10 perfluoroalkanesulfonic acids (PFSAs), methyl-perfluorooctane sulfonamide acetic acid (MeFOSAA, a PFSA precursor), and unknown C6-8 PFCA and perfluorooctanesulfonic acid precursors were frequently found in bioretention media and forebay sediments at Σ35PFAS concentrations of <0.03-19 and 0.064-16 µg/kg-DW, respectively. Unknown C6-8 PFCA precursor concentrations were up to ten times higher than the corresponding PFCAs, especially at forebays and biofilters' top layer. No significant trend could be attributed to PFAS and precursor concentrations versus depth of filter media, though PFAS concentrations were 2-3 times higher in the upper layers on average (significant difference between the upper (0-5 cm) and deepest (35-50 cm) layer). PFASs had a similar spatial concentration distribution in each filter media (no clear difference between short- and long-chain PFASs). Commercial land use and organic matter were important factors explaining the concentration variations among the biofilters and between the sampling depths, respectively. Given the comparable PFAS accumulations in deeper and superficial layers and possible increased mobility after precursor biotransformation, designing shallow-depth, nonamended sand biofilters or maintaining only the top layer may be insufficient for stormwater PFAS management.

Bioretention Design Modifications Increase the Simulated Capture of Hydrophobic and Hydrophilic Trace Organic Compounds.

Stormwater rapidly moves trace organic contaminants (TrOCs) from the built environment to the aquatic environment. Bioretention cells reduce loadings of some TrOCs, but they struggle with hydrophilic compounds. Herein, we assessed the potential to enhance TrOC removal via changes in bioretention system design by simulating the fate of seven high-priority stormwater TrOCs (e.g., PFOA, 6PPD-quinone, PAHs) with log KOC values between -1.5 and 6.74 in a bioretention cell. We evaluated eight design and management interventions for three illustrative use cases representing a highway, a residential area, and an airport. We suggest two metrics of performance: mass advected to the sewer network, which poses an acute risk to aquatic ecosystems, and total mass advected from the system, which poses a longer-term risk for persistent compounds. The optimized designs for each use case reduced effluent loadings of all but the most polar compound (PFOA) to <5% of influent mass. Our results suggest that having the largest possible system area allowed bioretention systems to provide benefits during larger events, which improved performance for all compounds. To improve performance for the most hydrophilic TrOCs, an amendment like biochar was necessary; field-scale research is needed to confirm this result. Our results showed that changing the design of bioretention systems can allow them to effectively capture TrOCs with a wide range of physicochemical properties, protecting human health and aquatic species from chemical impacts.

Effect of tire wear particle accumulation on nitrogen removal and greenhouse gases abatement in bioretention systems: Soil characteristics, microbial community, and functional genes.

Tire wear particles (TWPs), as predominant microplastics (MPs) in road runoff, can be captured and retained by bioretention systems (BRS). This study aimed to investigate the effect of TWPs accumulation on nitrogen processes, focusing on soil characteristics, microbial community, and functional genes. Two groups of lab-scale bioretention columns containing TWPs (0 and 100 mg g-1) were established. The removal efficiencies of NH4+-N and TN in BRS significantly decreased by 7.60%-24.79% and 1.98%-11.09%, respectively, during the 101 days of TWPs exposure. Interestingly, the emission fluxes of N2O and CO2 were significantly decreased, while the emission flux of CH4 was substantially increased. Furthermore, prolonged TWPs exposure significantly influenced the contents of soil organic matter (increased by 27.07%) and NH4+-N (decreased by 42.15%) in the planting layer. TWPs exposure also significantly increased dehydrogenase activity and substrate-induced respiration rate, thereby promoting microbial metabolism. Microbial sequencing results revealed that TWPs decreased the relative abundance of nitrifying bacteria (Nitrospira and Nitrosomonas) and denitrifying bacteria (Dechloromonas and Thauera), reducing the nitrification rate by 42.24%. PICRUSt2 analysis further indicated that TWPs changed the relative abundance of functional genes related to nitrogen and enzyme-coding genes.

Biochar and zero-valent iron alleviated sulfamethoxazole and tetracycline co-stress on the long-term system performance of bioretention cells: Insights into microbial community, antibiotic resistance genes and functional genes.

Antibiotics and antibiotic resistance genes (ARGs), known as emerging contaminants, have raised widespread concern due to their potential environmental and human health risks. In this study, a conventional bioretention cell (C-BRC) and three modified bioretention cells with biochar (BC-BRC), microbial fuel cell coupled/biochar (EBC-BRC) and zero-valent iron/biochar (Fe/BC-BRC) were established and two antibiotics, namely sulfamethoxazole (SMX) and tetracycline (TC), were introduced into the systems in order to thoroughly investigate the co-stress associated with the long-term removal of pollutants, dynamics of microbial community, ARGs and functional genes in wastewater treatment. The results demonstrated that the SMX and TC co-stress significantly inhibited the removal of total nitrogen (TN) (C-BRC: 37.46%; BC-BRC: 41.64%; EBC-BRC: 55.60%) and total phosphorous (TP) (C-BRC: 53.11%; BC-BRC: 55.36%; EBC-BRC: 62.87%) in C-BRC, BC-BRC and EBC-BRC, respectively, while Fe/BC-BRC exhibited profoundly stable and high removal efficiencies (TN: 89.33%; TP: 98.36%). Remarkably, greater than 99% removals of SMX and TC were achieved in three modified BRCs compared with C-BRC (SMX: 30.86 %; TC: 59.29%). The decreasing absolute abundances of denitrifying bacteria and the low denitrification functional genes (nirK: 2.80 × 105-5.97 × 105 copies/g; nirS: 7.22 × 105-1.69 × 106 copies/g) were responsible for the lower TN removals in C-BRC, BC-BRC and EBC-BRC. The amendment of Fe/BC successfully detoxified SMX and TC to functional bacteria. Furthermore, the co-stress of antibiotics stimulated the propagation of ARGs (sulI, sulII, tetA and tetC) in substrates of all BRCs and only Fe/BC-BRC effectively reduced all the ARGs in effluent by an order of magnitude. The findings contribute to developing robust ecological wastewater treatment technologies to simultaneously remove nutrients and multiple antibiotics.

Sulfoaluminate cement-modified loess as bioretention cell filler for nutrient removal from stormwater runoff.

In order to reduce the consumption of sand and gravel resources, the use of loess can reduce transportation costs and realize the in-situ construction of spongy in areas with rich loess resources. But the collapsibility and low permeability of loess make it unable to be directly used as the filler of bioretention cells. In this study, sulfoaluminate cement (SAC) mixed with a small amount of basalt fiber was considered to be used for loess modification, and the physicochemical properties and nutrient removal effect of SAC-modified loess as filler in bioretention cells were comprehensively evaluated. The results showed that when the SAC dosage was 15% and the basalt fiber addition was 0% (S15B0) and 0.6% (S15B6) and the curing time was 14 days, the stability and appropriate permeability can be exhibited, which can preliminarily satisfy the requirements of bioretention cell. SAC made the maximum adsorption capacity of S15B0 and S15B6 for ammonia nitrogen (NH4+-N) and phosphate higher than that of sand by 10.96%-31.51% and 45.92%-76.72%, respectively. The hydration products in SAC modified loess can fill the internal pores of loess particles and provide structural support, and ultimately reduce the accumulated pores, mesoporous pore size (20%) and surface homogeneity. Both S15B0 and S15B6 showed good removal effects of NH4+-N and COD. The TP removal efficiency was stable at 95.43%∼99.95%. Both the antecedent drying days and the submerged zone have an effect on the nitrogen removal in the bioretention cells, where a longer antecedent drying days is detrimental to the nitrogen removal, and the installation of a submerged zone improves the nitrogen removal. The basalt fiber can enhance the transformation process from nitrate-nitrogen to nitrite-nitrogen in the bioretention cell. Therefore, the modification of SAC can provide a certain idea for the in-situ use of loess as the filler of the bioretention cell.

Accumulation of typical persistent organic pollutants and heavy metals in bioretention facilities: Distribution, risk assessment, and microbial community impact.

Bioretention facilities have proven highly effective in removing pollutants from runoff. However, there is a concerning paucity of research on the contamination characteristics and associated risks posed by refractory pollutants in these facilities following long-term operation. This research focuses on the distribution, sources, microbial community impact, and human health risks of pollutants in eight bioretention facilities that have been operational for 5-11 years. The results showed that the distribution of Cu, Zn, and Cd was closely related to anti-seepage measures. PAHs, PCBs, and OCPs primarily accumulated in the surface, with concentrations ranging from 7.42 to 20.34 mg/kg, 31.8-77.3 µg/kg, and 60.5-163.6 µg/kg, respectively. Their concentrations inversely correlate with the depth of the media. Although the majority of contaminants remained below their respective risk thresholds, their concentrations typically exceeded those of background soil values, indicating an enrichment phenomenon. Source analysis revealed that PAHs primarily originate from oil combustion, PCBs were linked to their related industrial products, DDTs had their main sources in technical DDx and residues from the use of dicofol, while HCHs were traced back to historical residues from agricultural activities. Microbial α-diversity (Chao 1 and Shannon) decreased by 8.3-23.4% and 0.8-4.4%, respectively, in different facilities after long-term operation. The most dominant microbial phylum in the facilities was Proteobacteria (all relative abundances >48%). The total relative abundance of dominant genera was 6.7-34.3% higher than the control site, and Pseudomonas, a typical POPs-heavy metal degrading bacterium, had the highest relative abundance (>1.2%). Cu, Zn, and Cd present no non-carcinogenic risks and have low potential ecological risks. However, the lifetime cancer risk for PAHs is 10-6 ∼10-4 in most facilities and is of concern. The cancer risk for PCBs is acceptable, while OCPs pose a low cancer risk only for children.

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.

Compare individual and combined bioretention systems on the reduction of thermal pollution from stormwater runoff.

Urban surface temperatures are high in summertime, and thermal pollution caused by heat transfer from pavement to stormwater runoff is harmful to aquatic ecosystems. However, there is a lack of studies investigating the temperature change pattern during rainstorms and evaluating the effects of bioretention on dynamic characteristics of thermal pollution. Therefore, this study selected a 1.05 ha parking lot retrofitted with five individual bioretention cells in Beijing as the object to compare the temperature and volume of stormwater runoff before and after bioretention treatment. In the LID parking lot, the average EMT and EMXT (event maximum temperature) of runoff decreased by 2.28 °C and 4.18 °C, respectively, and the median percent thermal load reduction was 90.6%. Data analysis from 15 summer rainfall events showed that the sequence of factors affecting runoff EMT (event mean temperature) was average air temperature, max air temperature, max solar radiation, and rainfall peak 5-min intensity. Bioretention profoundly changed the thermal dynamic characteristics of stormwater runoff. Surface runoff temperatures generally showed a decreasing trend over time. The temperature change pattern of LID parking lot outflow was synchronized with that of the inflow and varied with different grades of precipitation. The probability of the peak temperature ahead of peak flow decreased from 80% to 53%, suggesting that 27% of the thermal first-flush effect of thermal pollution from the urban surface was alleviated by site-scale bioretention implementation. The site-scale bioretention combination had a lower effluent temperature and a higher thermal load reduction rate than single-scale solutions. These results fill the gap in research on the thermal pollution reduction process of bioretention. Furthermore, they can guide the optimization of bioretention design methods and strategies to protect urban water bodies from the stormwater runoff thermal pollution.

Investigation of pollutants accumulation in the submerged zone for pyrite-based bioretention facilities under continuous rainfall events.

Submerged zone in bioretention facilities for stormwater treatment has been approved to be an effective structure amendment to improve denitrification capability. However, the role and influence of water quality changes in the submerged zone under natural continuous random rainfall patterns are still not clear, especially when the rainfall is less than the pore water in the submerged zone. In this study, continuous rainfall events with different rainfall volume (light rain-light rain-heavy rain) were designed in a lab-scale woodchip mulched pyrite bioretention facility to test the effects of rainfall pattern. The results exhibited that light rain events significantly affected the pollutant removal performance of bioretention for the next rainfall. Different effects were observed during the long-term operation. In the 5th month, light rain reduced the ammonia removal efficiency of subsequent rainstorm events by 8.70%, while in the 12th month, when nitrate leakage occurred, light rain led to a 40.24% reduction in the next heavy rain event's nitrate removal efficiency. Additionally, light rain would also affect the concentration of by-products in the next rainfall. Following a light rain, the concentration of sulfate in the subsequent light rainfall can increase by 24.4 mg/L, and by 11.92 mg/L in a heavy rain. The water quality in the submerged zone and media characteristics analysis suggested that nitrogen conversion capacity of the substrate and microbes, such as Nitrospira (2.86%) and Thiobacillus (35.71%), as well as the in-situ accumulation of pollutants under light rain played important roles. This study clarifies the relationship between successive rainfall events and provides a more comprehensive understanding of bioretention facilities. This is beneficial for field study of bioretention facilities in the face of complex rainfall events.

The impact of recycling polyaluminium chloride and anionic polyacrylamide water treatment residuals on heavy metal adsorption in soils: implications for stormwater bioretention systems.

Despite the high adsorption capacity of polyaluminum chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) for Pb2+, Cd2+, Cu2+, and Zn2+, their influence on the adsorption behavior of heavy metals in traditional bioretention soil media remains unclear. This study investigated the impact of PAC-APAM WTRs at a 20% weight ratio on the adsorption removal of Pb2+, Cd2+, Cu2+, and Zn2+ in three types of soils. The results demonstrated improved heavy metal adsorption in the presence of PAC-APAM WTRs, with enhanced removal observed at higher pH levels and temperatures. The addition of PAC-APAM WTRs augmented the maximum adsorption capacity for Pb2+ (from 0.98 to 3.98%), Cd2+ (from 0.52 to 10.99%), Cu2+ (from 3.69 to 36.79%), and Zn2+ (from 2.63 to 13.46%). The Langmuir model better described the data in soils with and without PAC-APAM WTRs. The pseudo-second-order model more accurately described the adsorption process, revealing an irreversible chemical process, although qe demonstrated improvement with the addition of PAC-APAM WTRs. This study affirms the potential of PAC-APAM WTRs as an amendment for mitigating heavy metal pollution in stormwater bioretention systems. Further exploration of the engineering application of PAC-APAM WTRs, particularly in field conditions for the removal of dissolved heavy metals, is recommended.

Pollutant removal in an experimental bioretention cell situated in a northern Chinese sponge city.

To assess the viability and effectiveness of bioretention cell in enhancing rainwater resource utilization within sponge cities, this study employs field monitoring, laboratory testing, and statistical analysis to evaluate the water purification capabilities of bioretention cell. Findings indicate a marked purification impact on surface runoff, with removal efficiencies of 59.81% for suspended solids (SS), 39.01% for chemical oxygen demand (COD), 37.53% for ammonia nitrogen (NH3-N), and 30.49% for total phosphorus (TP). The treated water largely complies with rainwater reuse guidelines and tertiary sewage discharge standards. Notably, while previous research in China has emphasized water volume control in sponge city infrastructures, less attention has been given to the qualitative aspects and field-based evaluations. This research not only fills that gap but also offers valuable insights and practical implications for bioretention cell integration into sponge city development. Moreover, the methodology and outcomes of this study serve as a benchmark for future sponge city project assessments, offering guidance to relevant authorities.

Removal effect of pollutants from stormwater runoff in shallow bioretention system with gramineous plants.

The bioretention system is one of the most widely used low impact development (LID) facilities with efficient purification capacity for stormwater, and its planting design has been a hot spot for research at home and abroad. In this paper, ryegrass (Lolium perenne L.), bermuda (Cynodon dactylon Linn.), bahiagrass (Paspalum notatum Flugge), and green grass (Cynodon dactylon × C .transadlensis 'Tifdwarf') were chosen as plant species to construct a shallow bioretention system. The growth traits and nutrient absorption ability of four gramineous plants were analyzed. Their tolerance, enrichment, and transportation capacity were also evaluated to compare plant species and their absorptive capacity of heavy metals (Cu, Pb, and Zn). Results showed that the maximum absorption rate (Imax) ranged from 22.1 to 42.4 µg/(g·h) for P and ranged from 65.4 to 104.8 µg/(g·h) for NH4+-N; ryegrass had the strongest absorption capacity for heavy metals and the maximum removal rates of Cu, Pb, and Zn by four grasses were 78.4, 59.4, and 51.3%, respectively; the bioretention cell with ryegrass (3#) was significantly more effective in purifying than the unplanted bioretention cell (1#) during the simulated rainfall test. Overall, the system parameters were optimized to improve the technical application of gramineous plants in the bioretention system.

Application of multi-criteria decision-making on low-impact development practice selection for the Kinyerezi River sub-catchments in Dar es Salaam, Tanzania.

The impermeable areas in catchments are proportional to peak flows that result in floods in river reaches where the flow-carrying capacity is inadequate. The high rate of urbanization witnessed in the Kinyerezi River catchment in Dar es Salaam city has been noted to contribute to floods and siltation in the Msimbazi River. The Low-Impact Development (LID) practices that includes bio-retention (BR) ponds, rain barrels (RBs), green roofs (GRs), etc. can be utilized to mitigate portion of the surface runoff. This study aims to propose suitable LID practices and their sizes for mitigating runoff floods in the Kinyerezi River catchment using the Multi-Criteria Decision-Making (MCDM) approach. The results indicated that the BR and RBs were ranked high in capturing the surface runoff while the sediment control fences were observed to be the best in reducing sediments flowing into the BR. The proposed BR ponds were greater than 800 m2 with 1.2 m depth while RB sizes for Kinyerezi and Kisungu secondary schools and Kinyerezi and Kifuru primary schools were 2,730; 2,748; 1,385; and 1,020 m3, respectively. The BR ponds and RBs are capable of promoting water-demanding economic activities such as horticulture, gardening, car washing while reducing the school expenses and runoff generation.

Efficient nitrogen removal through coupling biochar with zero-valent iron by different packing modes in bioretention system.

Three kinds of bioretention were designed to explore the effects of zero-valent iron (ZVI) and biochar on the nitrogen removal performance and to seek a more reasonable packing method in this study. The results showed that the effluent removal rates of nitrate, ammonium and total nitrogen were 53.30 ± 12.68%, 98.41 ± 0.38% and 64.03 ± 8.72% respectively in Bioretention-3 during the rainfall events, while the nitrate concentration decreased gradually with the increase of drying time. According to the batch experiment, it was found that zero-valent iron could release continuously and stably in Bioretention-3 and Bioretention-1 due to the interception effect of biochar on dissolved oxygen. In addition, biochar in soil layer could protect zero-valent iron from excessive oxidation while biochar in the substrate layer could release organic matter to promote heterotrophic denitrification. Microbial community analysis showed that the dominant phyla were Proteobacteria (20.92-40.81%) and Actinobacteriota (9.89-24.54%). The dominant nitrifying genera was Nitrospira while there were also aerobic denitrifying bacteria (Sphingomonas, Bradyrhizobium and Chryseolinea, etc.) in soil layer. In the substrate layer, there was more ferrous iron-mediated autotrophic denitrification process (Thiobacillus, Geobacter and Denitratisoma, etc.) in Bioretention-1 and Bioretention-3 while a larger proportion of Dissimilatory Nitrate Reduction to Ammonium process (DNRA) (Bacillus, Desulfovibrio and Pseudomonas, etc.) in Bioretention-2. In general, this study showed that biochar addition in soil coupled with mixing zero-valent iron and biochar as substrate layer was a more stable and efficient design through various aspects of evidence. It provides a new way for how to use zero-valent iron and biochar to improve nitrogen removal capacity in stormwater management.

Sensors for Biomass Monitoring in Vegetated Green Infrastructure: A Review.

Bioretention cells, or rain gardens, can effectively reduce many contaminants in polluted stormwater through phytoremediation and bioremediation. The vegetated soil structure develops bacterial communities both within the soil and around the vegetation roots that play a significant role in the bioremediative process. Prediction of a bioretention cell's performance and efficacy is essential to the design process, operation, and maintenance throughout the design life of the cell. One of the key hurdles to these important issues and, therefore, to appropriate designs, is the lack of effective and inexpensive devices for monitoring and quantitatively assessing this bioremediative process in the field. This research reviews the available technologies for biomass monitoring and assesses their potential for quantifying bioremediative processes in rain gardens. The methods are discussed based on accuracy and calibration requirements, potential for use in situ, in real-time, and for characterizing biofilm formation in media that undergoes large fluctuations in nutrient supply. The methods discussed are microscopical, piezoelectric, fiber-optic, thermometric, and electrochemical. Microscopical methods are precluded from field use but would be essential to the calibration and verification of any field-based sensor. Piezoelectric, fiber-optic, thermometric, and some of the electrochemical-based methods reviewed come with limitations by way of support mechanisms or insufficient detection limits. The impedance-based electrochemical method shows the most promise for applications in rain gardens, and it is supported by microscopical methods for calibration and validation.

Biochar and fungi as bioretention amendments for bacteria and PAH removal from stormwater.

Bioretention has been widely used to mitigate hydrologic impacts of stormwater runoff and is increasingly being relied upon to treat chemical and biological pollutants transported by stormwater. Despite this reliance, we still lack an understanding of treatment performance for certain organic and biological contaminants which may interact with biotic and abiotic components of bioretention systems. We evaluated the treatment of fecal indicator bacteria (FIB) and polycyclic aromatic hydrocarbons (PAHs) in stormwater runoff by bioretention. We compared treatment performance by Washington's standard bioretention mix of 60% sand: 40% compost (by volume), and by three other mixtures amended with biochar, fungi (Stropharia rugosoannulata), or both. All bioretention columns were conditioned with clean water and then dosed with collected roadway runoff at a rate equivalent to a 6 month, 24 h storm in this region during 8 events over a 14-month period. Effluents for each column were analyzed for 23 PAHs, Escherichia coli, fecal coliform, dissolved organic carbon (DOC), and total suspended solids (TSS). The fate and transport of PAHs within the bioretention columns was tracked by measuring soil PAHs in media cores taken from the columns. ΣPAH were almost completely removed by all treatments across all storms, with removal rates ranging from 97 to 100% for 94 out of 96 samples. Compost appeared to be a source of PAHs in bioretention media, as biochar-amended media initially contained half the ΣPAHs as treatments with the standard 60:40 sand:compost mixture. We observed a net loss of ΣPAHs (19-73%) in bioretention media across the study, which could not be explained by PAHs in the effluent, suggesting that bioremediation by microbes and/or plants attenuated media PAHs. E. coli and fecal coliform were exported in the first dosing event, but all columns achieved some treatment in subsequent dosing events. Overall, these findings suggest that PAHs in stormwater can be remediated with bioretention, are unlikely to accumulate in bioretention media, and that biochar amendments can improve the treatment of E. coli.

Effects of freeze-thaw cycles on nutrient removal from bioretention cells.

There have been numerous summaries of the runoff purification characteristics of bioretention cells in warm climates. However, little has been done on the effects of freeze-thaw cycles (FTCs) that frequently occur in cold regions on bioretention cell performance. Three experimental columns were constructed to simulate the operation of the bioretention cell under the FTCs. The effects of FTCs on the nutrient removal efficiency of different filling bioretention cells were analyzed. The results showed that the ammonia nitrogen (NH4+-N) concentration in the effluent of the wood chip bioretention cell under the T3 conditions (WBCF) (2.35 mg/L) was significantly higher than that of the wood chip bioretention cell operating at room temperature (WBCR) (0.62 mg/L). The effluent NH4+-N concentration of aluminum sludge bioretention cell (ABCF) (0.096 mg/L) under the FTCs was lower than that of WBCF (0.91 mg/L). Under the T3 condition, the effluent nitrate nitrogen (NO3--N) and total nitrogen (TN) concentrations of WBCF (5.33 mg/L and 8.86 mg/L) were higher than those of WBCR (5 mg/L and 6.11 mg/L) at room temperature. Under FTCs conditions, both WBCF and ABCF had high NO3--N removal efficiency (up to 85.87% and 24.75%) at the initial stage of thawing of the filler, and the efficiency gradually decreased with the thawing of the filler. With the increase of FTCs, the NO3--N removal efficiency of WBCF gradually decreased (always higher than 13.6%), while the removal efficiency of ABCF fluctuated wildly (the removal efficiency was primarily negative). The total phosphorus (TP) concentration in the effluent of WBCF (0.11 mg/L) under the T3 conditions was lower than that of WBCR (0.02 mg/L) at room temperature, and the TP concentration of ABCF (0.021 mg/L) in the effluent under the FTCs was slightly lower than that of WBCF (0.031 mg/L). The FTCs have a more significant impact on removing nitrogen pollutants in runoff, but have little effect on phosphorus. Compared with aluminum sludge, wood chips are more suitable for efficient removal of nitrogen pollutants in runoff under the FTCs. The experimental conclusions can provide a reference for the construction of bioretention cells in cold regions.

Impact of wood-derived biochar on the hydrologic performance of bioretention media: Effects on aggregation, root growth, and water retention.

Bioretention systems are one example of green stormwater infrastructure that may mitigate the hydrologic impact of stormwater runoff. To improve water retention while maintaining rapid stormwater infiltration, conventional bioretention soil media (BSM) might be augmented with biochar. Biochar may improve the BSM's structure by increasing soil aggregation, which might improve water retention and increase stormwater infiltration while also improving root growth. Pots with BSMs representing high and moderate sand content media were amended with a wood-derived biochar, planted with switchgrass, and subjected to weekly storms for 20 weeks, followed by a 10-week drought. In the high sand content medium (NC mix), biochar amendment increased hydraulic conductivity (Ksat), and this effect increased with time. At 0 weeks, 2% and 4% (w/w) biochar increased Ksat by 4 ± 2% and 10 ± 4%, respectively, while at 30 weeks the increase was 30 ± 10 and 70 ± 20%, respectively, above biochar-free media. Similar improvements were seen in plant available water (PAW) in NC mix. However, minimal improvements in Ksat and PAW from biochar amendment were found in the moderate sand content BSM that contained compost and mulch (DE mix). Where biochar promoted Ksat, this was correlated with increased water-stable aggregate size (r = 0.86), fine root volume (r = 0.88), and below ground biomass (r = 0.83). Important factors affecting Ksat and aggregation in the NC mix were biochar's influence on organo-mineral association, fungal hyphae length, and plant roots. Wood-derived biochar amendment to BSM may obviate the need for compost/mulch since biochar has similar effects on improving BSM hydrology and root growth without the risk of undesired nutrient leaching.

Performance evaluation of a low-cost loess-based filler for bioretention cells.

The sand and gravel fillers used in traditional bioretention cells are expensive and becoming increasingly scarce, and their performance is unstable. It is important to find a stable, reliable, and low-cost alternative filler for bioretention facilities. Using cement as a modified loess filler for bioretention cells is a low-cost and easily obtainable alternative. The loss rate and anti-scouring index of the cement-modified loess (CM) were analyzed under different curing times, cement addition amount, and compactness control conditions. This study found that the stability and strength of the cement-modified loess in water with a density of not less than 1.3 g/cm3, a curing time, of not less than 28 d and a cement addition amount not less than 10% meets the use requirements of the bioretention cell filler. X-ray diffraction and Fourier transform infrared spectroscopy of cement-modified materials with a 10% cement addition and a curing time of 28 days (CM28) and 56 days (CM56). Cement-modified materials with 2% straw and a curing time of 56 days (CS56) showed that the three kinds of modified loess all contain calcium carbonate and that the surface contains hydroxyl and amino functional groups that can effectively remove phosphorus. The specific surface areas of the CM56, CM28, and CS56 samples were 12.53 m2/g, 24.731 m2/g, and 26.252 m2/g, respectively, which are significantly higher than that of sand (0.791 m2/g). At the same time, the adsorption capacity of the ammonia nitrogen and the phosphate that was present in the three modified materials is better than that of sand. CM56, like sand, has rich microbial communities, which can entirely remove nitrate nitrogen in water under anaerobic conditions, indicating that CM56 can be used as an alternative filler for bioretention cells. The production of cement-modified loess is simple and cost-effective, and using modified loess as a filler can reduce the use of stone resources or other on-site materials. Current methods for improving the filler of bioretention cells are mainly based on sand. This experiment used loess to improve the filler. The performance of loess is better than sand, and can completely replace sand as the filler in bioretention cells.

Understanding a wood-derived biochar's impact on stormwater quality, plant growth, and survivability in bioretention soil mixtures.

Bioretention systems are planted media filters used in stormwater infrastructure. Maintaining plant growth and survival is challenging because most designs require significant sand. Conventional bioretention soil media (BSM) might be augmented with biochar to make the BSM more favorable to plants, to improve nutrient removal efficiency, and enhance plant survivability during drought while replacing compost/mulch components that have been linked to excess nutrient export. Pots with BSMs representing high and moderate sand content were amended with wood biochar, planted with switchgrass, and subjected to weekly storms for 20 weeks, followed by a 10-week drought. After 20 weeks, 4% biochar amendment significantly increased stormwater infiltration (67%) and plant available water (52%) in the high sand content BSM (NC mix, which meets requirements for the state of North Carolina (US) and contains no compost/mulch), and these favorable hydraulic properties were not statistically different from a moderate sand content, biochar-free BSM with compost/mulch (DE mix, which meets requirements for state of Delaware (US)). While biochar amendment improved plant height (25%), the number of shoots (89%), and total biomass (70%) in the NC mix, these parameters were still less than those in the biochar-free DE mix containing compost/mulch. TN and NO3-1 removal were also improved (28-35%) by biochar amendment to NC mix, and the resulting TN and TP loadings to groundwater were 10 and 7 times less, respectively than biochar-free DE mix with compost/mulch. During the drought period, biochar amendment increased the time to switchgrass wilting by ∼8 days in the NC mix but remained 40% less than the biochar-free DE mix. A recalcitrant carbon-like biochar mitigates some of the deleterious effects of high sand content BSM on plants, and where nutrient pollution is a concern, replacement of compost/mulch with wood biochar in BSM may be desired.