Bioretention Soil Media Research Articles

Removal, accumulation, and micro-ecosystem impacts of typical POPs in bioretention systems with different media: A runoff infiltration study

Bioretention systems prove effective in purifying common persistent organic pollutants (POPs) found in urban rainfall runoff. However, the response process of the microecosystem in the media becomes unclear when POPs accumulate in bioretention systems. In this study, we constructed bioretention systems and conducted simulated rainfall tests to elucidate the evolution of micro-ecosystems within the media under typical POPs pollution. The results showed all POPs in runoff were effectively removed by surface adsorption in different media, with load reduction rates of >85 % for PCBs and OCPs and > 80 % for PAHs. Bioretention soil media (BSM) + water treatment residuals (WTR) media exhibited greater stability in response to POPs contamination compared to BSM and pure soil (PS) media. POPs contamination significantly impacted the microecology of the media, reducing the number of microbial species by >52.6 % and reducing diversity by >27.6 % at the peak of their accumulation. Enzyme activities were significantly inhibited, with reductions ranging from 44.42 % to 60.33 %. Meanwhile, in terms of ecological functions, the metabolism of exogenous carbon sources significantly increased (p < 0.05), while nitrogen and sulfur cycling processes were suppressed. Microbial diversity and enzyme activities showed some recovery during the dissipation of POPs but did not reach the level observed before the experiment. Dominant bacterial species and abundance changed significantly during the experiment. Proteobacteria were suppressed, but remained the dominant phylum (all relative abundances >41 %). Bacteroidota, Firmicutes, and Actinobacteria adapted well to the contamination. Pseudomonas, a typical POPs-degrading bacterium, displayed a positive correlation between its relative abundance and POPs levels (mean > 10 %). Additionally, POPs and media properties, including TN and pH, are crucial factors that collectively shape the microbial community. This study provides new insights into the impacts of POPs contamination on the microbial community of the media, which can improve media design and operation efficiency.

Characterization and microbial mechanism of pollutant removal from stormwater runoff in the composite filler bioretention system

Abstract Bioretention systems are a low-impact development (LID) measure to effectively control stormwater runoff and reduce pollutant concentrations. In this paper, three groups of bioretention cells with different filling materials (1# bioretention soil media (BSM), 2# BSM + 5% biochar, and 3# BSM +5% biochar +biological filler) were constructed to analyze the pollutant removal characteristics and microbial action under different simulated rainfall conditions. Results showed that the overall pollutant removal capacity of systems 2# and 3# was higher than that of system 1#, with system 3# having the lowest effluent concentrations of 2.71 mg/L for total nitrogen (TN) and 64.3 mg/L for chemical oxygen demand (COD). The load reduction effect for heavy metals of the three systems was ranked as 2# &amp;gt; 1# &amp;gt; 3#, and average load reduction rates were 80.3, 75.1, and 84.8% for Cu, Pb, and Zn in 2#. Microbial community analysis indicated that Proteobacteria and Firmicutes were the absolute dominant bacteria of the three bioretention systems, and the dominant genera included Bacillus, Hyphomicrobium, Micrococcaceae, and Nitrospira. In addition, the total number of denitrifying functional bacteria genera in systems 2# and 3# was increased by 1.39 and 52.1% compared to system 1#.

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.

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.

Metabolism characteristics of nitrogen functional microorganisms in bioretention system under multiple dry-wet alternation

In this study, we used metagenomic sequencing to explore the metabolism characteristics of nitrogen-cycling microorganisms in a bioretention system under multiple dry-wet alternation conditions. The results revealed that different dry-wet alternation conditions affected the composition of nitrogen-cycling microbes in bioretention soil media (BSM). In addition, the metagenomic analyses showed a higher relative abundance of key denitrifiers (Proteobacteria and Actinobacteria) under constant periods than unordered period. Furthermore, there was increased expression of nitrification functional genes and decreased expression of denitrifying functional genes during the unordered period, leading to nitrate accumulation in BSM. Under the constant dry-wet conditions, a short dry period (5 d) was shown to be beneficial to the nitrate reduction process. However, there was a risk of nitrite accumulation, which could be improved by rewetting. Moreover, our data proved that the NADH production process was inhibited in unordered period, causing nitrate accumulating. In conclusion, this study revealed that the different dry-wet alternation conditions could drive the expression of nitrogen functional genes, thus affected the biological nitrogen metabolism in bioretention systems.

Study of pollutant accumulation characteristics and microbial community impact at three bioretention facilities.

In this paper, three bioretention facilities (BT, RG1-A, and RG1-B) were selected for on-site testing and experimental analysis. Of which, BT is a roadside bioretention tank with layered filler, while RG1-A and RG1-B are rain gardens with conventional filler (Bioretention soil media, BSM) and modified filler (BSM+10% Water treatment residuals,WTR), respectively. The effect of pollutant accumulation on the soil microbial community structure in the facilities, and the risk of heavy metal contamination over several years of bioretention facility operationwere studied. Results showed that the water quality pollutant load reduction in BT was fluctuating. This is related to the poor waterquality of roadstormwater flowing into BTand the facility filler. Because RG1-B uses modified filler, RG1-B was more effective than RG1-A in regulating water quality and quantity; the changes in soil physical and chemical properties in BT, RG1-A, and RG1-B were influenced by external factors. Next, BT was at high risk of heavy metal contamination than other facilities. The microbial community structure of the facility had the following characteristics: at the phylum level, Proteobacteria was the dominant phylum in the bioretention facility, accounting for 29-45%; and at the genus level, Blastocatella was the dominant phylum, and the relative abundance in situ was higher than that in the bioretention facility. The results of the correlation analysis combining filler environmental factors and microbial community structure indicated that SMC was a highly influential factor among the three facilities.

Optimization design of key parameters for bioretention cells with mixed filter media via HYDRUS-1D model and regression analysis

The structural design of bioretention cells (BRCs) is important for stormwater flood control and pollutant removal. How to determine the key parameters and their values that affect the operation effect of facilities is a key problem to be solved. Synthetic storm experiments were monitored and analyzed to determine these regulation effects. The BRC with filler of BSM (Bioretention soil media) +10% fly ash showed excellent water reduction rate and event mean concentration (EMC) removal rate. BSM was the mixture of sand, soil and wood chips, and the ratio was 65:30:5 by mass. Based on the experimental data, the sensitivity of model parameters in Hydrus-1D was defined by using the Morris classification screening method. The key hydrological and water quality parameters were calibrated and validated with a determination coefficient R2 above 0.6 and a Nash–Sutcliffe efficiency coefficient NSE above 0.5. The key structure parameters in BRCs were optimized by using the calibrated HYDRUS-1D model and the response surface methodology (RSM). Results show that the BRC with the filler of BSM + 10% fly ash has the smallest optimized thickness of the filler layer, while the BRC with the filler of BSM + 10% green zeolite is the largest, and the difference between the two media combination is 16–26 cm. The design return period and the confluence ratio affect the design water volume jointly. Under the three-year design return period, the confluence ratios of five kinds of filling combinations (BSM + 10% WTR, BSM + 10% fly ash, soil, BSM, BSM + 10% green zeolite) are recommended to be≤20:1, 20:1, 15:1, 15:1 and 10:1 respectively

Balancing Hydraulic Control and Phosphorus Removal in Bioretention Media Amended with Drinking Water Treatment Residuals.

Green stormwater infrastructure like bioretention can reduce stormwater runoff volumes and trap sediments and pollutants. However, bioretention soil media can be both a sink and source of phosphorus (P). We investigated the potential tradeoff between hydraulic conductivity and P sorption capacity in drinking water treatment residuals (DWTRs), with implications for bioretention media design. Batch isotherm and flow-through column experiments were used to quantify the maximum P sorption capacity (Smax) and rate of P sorption for three DWTR sources. Smax values varied greatly among DWTR sources and methodologies, which has implications for regulatory standards. We also conducted a large column experiment to determine the hydraulic and P removal effects of amending bioretention media with solid and mixed layers of DWTRs. When applied to bioretention media, the impact of DWTRs on hydraulic conductivity and P removal depended on layering strategy. Although DWTR addition in solid and mixed layer designs improved P removal, the solid layer restricted water flow and exhibited incomplete P removal, while the mixed layer had no effect on flow and removed ~100% of P inputs. We recommend that DWTRs be mixed with sand in bioretention media to simultaneously achieve stormwater drainage and P reduction goals in green stormwater infrastructure.

Bioretention System Enhancements for Nutrient Removal

Bioretention systems typically demonstrate limited nutrient treatment and often export nutrients just after installation. A variety of bioretention configurations were tested in duplicate field-scale mesocosms dosed with stormwater. A commercial bioretention soil media (BSM) was used by itself in some mesocosms and mixed with topsoil in others. Configurations tested included an activated alumina (AA) layer placed below the BSM, expanded gravel storage below the BSM, bottom outlets, and single and dual elevated outlets. Mesocosms with BSM/soil mix outperformed BSM-only mesocosms for both nitrogen and phosphorus removal. Mesocosms without AA exported considerable phosphorus. The AA layer substantially reduced phosphorus export and slightly improved nitrogen removal. Outlet types and elevations did not affect phosphorus removal. Compared to treatments with bottom drains, those with elevated outlets showed better nitrogen removal. The effectiveness of dual elevated outlets equaled or slightly exceeded single elevated outlets. Washing the media with tap water during construction reduced export only initially, with no differences noted after a few runs. The expanded storage mesocosms showed mixed results probably due to construction deficiencies.

Efficacy of Spent Lime as a Soil Amendment for Nutrient Retention in Bioretention Green Stormwater Infrastructure

The composition of bioretention soil media (BSM) is among the most critical design attributes contributing to the water quality performance of bioretention systems, as various amendments may increase the capacity for chemical sorption of certain nutrient pollutants. We investigated the spent lime (a calcium-based water treatment residual) as BSM amendments for nutrient retention. The study was conducted in two parts: the first was a field-based mesocosm experiment in which we assessed the effect of spent lime amendments on leachate nutrient concentration for treatments receiving different levels of phosphorus and nitrogen loading (simulated by different levels of compost added to the substrate). The second was a laboratory study comparing various levels of spent lime and coir on leachate nutrient concentration at two different simulated loading rates. Effluent water was collected and analyzed for PO43−, NH4+ and NO3− concentrations in the field and lab. Spent lime significantly reduced leachate PO43− concentrations (upwards of 50%) in both the field and lab mesocosm studies compared to treatments without spent lime. Reductions in NH4+ concentrations were also observed due to spent lime but with variable significance across the different compost levels, whereas NO3− concentrations were higher in plots with spent lime than plots without spent lime. In the lab, columns with coir had significantly higher leachate PO43− concentrations compared to spent lime-treated columns, however, leachate NH4+ and NO3− concentrations did not significantly differ between treatments at the same compost levels. This study shows that spent lime, which is a waste product, is effective in significantly reducing leachate PO43− concentrations from BSM, while be a cost-effective substitute to engineered proprietary media that is expensive to acquire; however, future studies must also evaluate its potential for clogging.

Reduction and Accumulative Characteristics of Dissolved Heavy Metals in Modified Bioretention Media

Twelve bioretention filter columns with different media were designed to study the effects of media on dissolved heavy metals in bioretention systems by changing three test conditions (inflow concentration, discharge ratio, and recurrence interval). The results showed that the average load reduction efficiency of the bioretention soil media (BSM)+10%water treatment residue, BSM+10%green zeolite, and BSM+10%medicinal stone for Cu and Zn was larger than 80%. The highest volume reduction efficiency is 39.25% by BSM+coconut bran. Among the three factors selected in tests, inflow concentration had the biggest degree of influence, followed by discharge ratio and recurrence interval. The media of the upper, middle, and lower layers of each filter column were detected before and after the treatment to study the accumulative characteristics of heavy metals in the bioretention system. The accumulation of Cu, Zn, and Cd in the media of BSM+medicinal stone, BSM+fly ash, BSM+vermiculite, and BSM+turfy soil was relatively low. The contents of the three metals were positively correlated with urease and negatively correlated with protease in the media, but no obvious rule was showed in the accumulation of dissolved heavy metals with depth.

Soil Media CO2 and N2O Fluxes Dynamics from Sand-Based Roadside Bioretention Systems

Green stormwater infrastructure such as bioretention is commonly implemented in urban areas for stormwater quality improvements. Although bioretention systems’ soil media and vegetation have the potential to increase carbon (C) and nitrogen (N) storage for climate change mitigation, this storage potential has not been rigorously studied, and any analysis of it must consider the question of whether bioretention emits greenhouse gases to the atmosphere. We monitored eight roadside bioretention cells for CO2-C and N2O-N fluxes during two growing seasons (May through October) in Vermont, USA. C and N stocks in the soil media layers, microbes, and aboveground vegetation were also quantified to determine the overall C and N balance. Our bioretention cells contained three different treatments: plant species mix (high diversity versus low diversity), soil media (presence or absence of P-sorbent filter layer), and hydrologic (enhanced rainfall and runoff in some cells). CO2-C and N2O-N fluxes from all cells averaged 194 mg m−2 h−1 (range: 37 to 374 mg m−2 h−1) and 10 µg m−2 h−1 (range: −1100 to 330 µg m−2 h−1), respectively. There were no treatment-induced changes on gas fluxes. CO2-C fluxes were highly significantly correlated with soil temperature (R2 = 0.68, p &lt; 0.0001), while N2O-N fluxes were weakly correlated with temperature (R2 = 0.017, p = 0.04). Bioretention soil media contained the largest pool of total C and N (17,122 g and 1236 g, respectively) when compared with vegetation and microbial pools. Microbial biomass C made up 14% (1936 g) of the total soil C in the upper 30 cm media layer. The total C and N sequestered by bioretention plants were 13,020 g and 320 g, respectively. After accounting for C and N losses via gas fluxes, the bioretention appeared to be a net sink for those nutrients. We also compared our bioretention gas fluxes to those from a variety of natural (i.e., grasslands and forests) and artificial (i.e., fertilized and irrigated or engineered) land-use types. We found bioretention fluxes to be in the mid-range among these land-use types, mostly likely due to organic matter (OM) influences on decomposition being similar to processes in natural systems.

Predictors of Phosphorus Leaching from Bioretention Soil Media.

The phosphorus saturation index (PSI) and P saturation ratio (PSR) were tested across a wide range of bioretention soil mixtures (BSMs) for their relationship to total and dissolved P in column leachate. The BSMs tested were made using different feedstocks including sand alone, food and yard waste compost, biosolids and yard compost, and high Fe biosolids. The PSI of the mixtures ranged from 0.23 ± 0.03 (biosolids and yard waste compost 15%, oyster shells 5%) to 1.26 ± 0.02 (biosolids and yard waste compost 80%). The PSR of the mixtures ranged from 0.05 ± 0 (100% sand) to 3.12 ± 0.12 (biosolids and yard waste compost 80%). A total of 12 storm events were staged using both synthetic rainwater (total P = 1.71 ± 0.3 mg L) and actual stormwater (total P = 0.08 ± 0.03 mg L). Excluding the sand-only mixture, all treatments were a source of P for the duration of the study. However both total and dissolved P concentrations decreased over time. Effluent concentrations of total P in the first event ranged from 0.59 to 75.55 mg L but decreased by the final event to between 0.15 and 10.73 mg L. The PSR was found to be a good predictor of P leaching from all BSMs with an of 0.73 for total mass of P leached across all leaching events. The PSI was a poor predictor ( < 0.3). The PSR also predicted total P in leachate for individual events more effectively than the PSI. Total P in the BSMs had no relationship to P in the leachate.

Lab-Scale Column Studies for Enhanced Phosphorus Sorption from Synthetic Urban Stormwater Using Modified Bioretention Media

AbstractBuilding on previous batch studies, this study further investigated the removal of dissolved organic P (DOP) using small (15 cm) columns with water treatment residual (WTR) and alum as two promising amendments to bioretention soil media (BSM). BSM modified with alum and WTR exhibited higher sorption capacity. Compared with unmodified BSM, significant improvements were observed for adenosine monophosphate (AMP), myo-inositol hexakisphosphate (IHP), and inorganic P (SRP) removal using 10% alum-modified WTR-amended BSM (WTR-BSM), by factors of 26, 7, and 150, respectively. The 10% alum-modified WTR-BSM reduced DOP levels<0.01 mg/L within 1 min of contact time, demonstrating more-rapid DOP sorption processes compared with unamended media. The oxalate ratio (OR), which is based on oxalate-extractable Al, Fe, and P, was employed to provide a criterion for BSM performance with respect to P sorption. Strong correlations (R2=0.92, 0.96, and 0.65 for AMP, IHP, and SRP, respectively) between the media OR an...

Enhanced Organic Phosphorus Sorption from Urban Stormwater Using Modified Bioretention Media: Batch Studies

AbstractDissolved organic phosphorus (DOP) has been found to be a significant fraction of the urban runoff phosphorus load. To achieve enhanced DOP removal, bioretention soil media (BSM) amended with an aluminum-based water treatment residual (WTR) and montmorillonite (both 10% by mass) were additionally treated with aluminum sulfate (10% by mass) to improve sorption capacities. The sorption of myo-Inositol hexakisphosphate (IHP) and adenosine monophosphate (AMP), two forms of organic phosphorus, by modified BSM were studied using batch experiments. The sorption of AMP was increased by a factor of 17 and 21 for WTR- and montmorillonite-amended BSM with 10% alum, respectively. Similarly, the IHP removal capacity of these two modified media mixtures were increased by factors of 4 and 5, respectively. Scanning electron microscopy (SEM) and Brunauer, Emmett, and Teller (BET) surface area analyses were used to provide support for underlying sorption mechanisms for the enhanced DOP removal. The oxalate ratio (O...

Water Treatment Residual as a Bioretention Amendment for Phosphorus. II: Long-Term Column Studies

Bioretention is an EPA-designated best management practice developed to mitigate negative ecological effects from urban storm-water. However, while these facilities perform well for the removal of a multitude of pollutants, in many cases they are ineffective in treating excessive storm-water nutrients such as phosphorus (P) that may induce surface water eutrophication. This work builds on the results of a previous paper, which describe initial studies on the use of aluminum-based water treatment residual (WTR) as a bioretention soil media (BSM) amendment. A 5% WTR-, 3% triple-shredded hardwood bark mulch-amended loamy sand BSM was investigated in a large-scale (0.9 m) column to determine the media P adsorption performance under varying hydrologic and pollutant concentration conditions. Results indicate that the WTR-amended media adsorbed 88.5% of the applied P mass, relative to a non-WTR-amended control media for which effluent P mass increased by 71.2%. The amended media consistently produced total phosp...

Water Treatment Residual as a Bioretention Amendment for Phosphorus. I: Evaluation Studies

Urban stormwater runoff has been implicated as a major source of excess nutrients to surface waters, contributing to the development of eutrophic conditions. Bioretention, a promising technology for urban stormwater pollution treatment, was investigated to determine whether an aluminum-based water treatment residual (WTR) amended bioretention soil media (BSM) could adsorb sufficient P at low concentrations (120 μg P L-1), extrapolated for a 20-year facility lifetime. Batch and minicolumn studies were employed to determine both an optimal BSM mixture and media performance. Media tests demonstrated P adsorption proportional to WTR addition. Additional amendments such as quartz sand and hardwood bark mulch produced further significant variations in adsorptive behavior. WTR-amended media showed excellent P removal, meeting the developed benchmark for adsorptive behavior. Predominantly, media met minimal P adsorption requirements when it contained at least 4 to 5% WTR by mass (air dried). The use of an oxalat...