Bioretention system mediated by different dry-wet alterations on nitrogen removal: Performance, fate, and microbial community

Application of construction waste residue-based compositing fillers in bioretention facility: Intensified nitrogen removal and mitigated by-product effects

Bioretention facilities (BRF) are widely utilized in sponge cities for stormwater management, but they face challenges in effectively controlling nitrogen due to the instability of traditional fillers. Pyrite has been extensively employed as an electron donor to enhance nitrogen removal; however, it generates by-products such as H+, SO42-, and Fe2+/Fe3+ that can pose environmental issues. Construction waste residues (CWR), consisting of waste brick and concrete, have been explored as alternative fillers, but they suffer from alkaline leaching problems. To mitigate this limitation, this study investigated the optimal packing location of a composite filler consisting of pyrite with CWR (a mixture of waste brick and concrete) within BRF, considering rainfall intensity and antecedent drying days. The synergetic pollution removal and by-product mitigate mechanism of waste residue-based composite fillers applied to BRF was elucidated through SEM and FTIR characterizations, as well as microbial community analysis. Results showed that incorporating 40% CWR in the vadose layer and 20% pyrite in the submerged layer significantly enhanced nitrogen removal while maintaining limited NO2--N accumulation in BRF (exceeding 80% TN), effectively controlling effluent pH levels and by-products (total Fe and SO42-) concentration within acceptable limits. CWR improved NH4+-N and TP adsorption capacity, whereas pyrite further increased NO3--N removal through autotrophic denitrification. Alkaline leaching from CWR was neutralized with H+ produced during autotrophic denitrification, forming Fe (oxyhydr)oxides with Fe3+ derived from pyrite oxidation; thus, achieving acceptable pH values and total Fe concentrations. Meanwhile, the media composite strategy successfully regulated effluent SO42- concentration by reducing Thauera and Thiobacillus abundance. Overall, this study demonstrates that integrating CWR with pyrite into BRF can facilitate stable and efficient pollutant removal while concurrently mitigating by-product issues.

Atrazine disrupts nitrogen removal performance and greenhouse gas abatement in bioretention systems: Unraveling microbiotas and macrophytes responses

The potential impact of stormwater runoff-induced loss of triazine herbicides, like atrazine (ATZ), on soil nitrogen cycling remains poorly understood. Bioretention systems (BRS) represent effective stormwater control measures (SCM) now understood to serve as important ATZ accumulation zones. However, the effects of ATZ exposure on nitrogen removal and greenhouse gas (GHG) abatement within BRS remain unclear. In the present study, bioretention columns were established and exposed to ATZ (0-25 mg kg-1) for 200 days. The results demonstrated that the accumulation of ATZ led to a reduction in total nitrogen removal efficiency (by 7.7-49.3 %) while simultaneously causing an increase in GHG emission fluxes (by 11.2 %-25.1 %). Moreover, ATZ significantly altered microbial activities, including nitrogen metabolism enzymes (hydroxylamine oxidoreductase, nitrate reductase, and nitrite reductase) and the electron transport system (ETSA). Microbial community analysis showed that ATZ reduced the relative abundance of nitrifying bacteria (Nitrospira and Nitrosomonas), along with certain denitrifying bacteria (Thauera, Terrimonas, and Dechloromona). Besides, the compromised function of leaves and roots diminished plant nitrogen uptake, and the application of structural equation modeling (SEM) revealed an increased contribution of plants to nitrogen removal. These findings collectively suggest that the widespread presence of triazine herbicides in urban areas could potentially impact the performance of SCMs.

Advanced treatment of first flush roof runoff via a dry-wet polymorphic constructed wetland system: Performance and mechanistic insights

Controlling runoff pollution is crucial to improving ecological environments in the context of urbanization and climate change. However, a significant research gap remains in the treatment and reuse of roof runoff, particularly during the first flush. To address this, a novel dry-wet polymorphic constructed wetland (DWP-CW) system was developed to purify first flush runoff efficiently and reliably. The performance and stability of the DWP-CW system were evaluated under varying conditions, including rainfall intensities, pollution load levels, and antecedent dry days (ADDs). The purification mechanisms and pollutant metabolism were further analyzed using bioinformatics. Results demonstrated that the DWP-CW system achieved excellent pollutant removal efficiencies, with average removal rates exceeding 99% for chemical oxygen demand (COD) and ammonia-nitrogen (NH3-N), and stable removal rates above 80% for total nitrogen (TN) and total phosphorus (TP). The dominant aerobic microbial community played a key role in the system's purification process, while the superior water-retention capacity of the upper sandy soil layer provided a favorable environment for microbial survival during ADDs. This study offers robust theoretical support for practical application of DWP-CW systems in runoff pollution control.

Optimizing irrigation and planting strategies to prevent non-point source pollution in the Hetao Irrigation District using SWAT-MODFLOW-RT3D model

Non-point source (NPS) pollution is a significant issue in the Hetao Irrigation District (HID), affecting local water environment and ecological safety. To explore solutions for managing NPS pollution in the HID, this study establishes the SWAT-MODFLOW-RT3D (SMFR) model based on data from recent years. The results show that the determination coefficient (R2) of monthly drainage simulation for both the calibration and validation periods are >0.6, the Nash-Sutcliffe efficiency (NSE) values are >0.7, and the percent bias (PBIAS) values are <10 %. For pollutant transport simulation (total nitrogen and total phosphorus), the R2 values for both calibration and validation periods exceed 0.6, the NSEs are >0.75, and the PBIAS values are below 20 %. The model demonstrates good performance in simulating hydrology and pollutant transport in the study area, indicating strong applicability. Building on this, the spatial and temporal distribution characteristics of nitrogen and phosphorus losses in the HID were analyzed, and the impacts of different agricultural management practices, such as irrigation and fertilization regimes, drip irrigation under film (DIUF), and crop structure adjustments, on NPS pollution were assessed. Extensive scenario testing indicates that deficit irrigation and DIUF reduce total nitrogen (TN) in agricultural NPS pollution by 7.74 % and 9.34 %, respectively, and total phosphorus (TP) by 35.12 % and 40.99 %, respectively. In contrast, crop structure adjustments have a relatively moderate reduction effect on TN and TP, ranging from 2.66 % to 6.80 %. Additionally, the study examines the NPS pollution control effects of various combined scenarios. Through economic benefit evaluation, it was found that the scenario combining deficit irrigation with crop structure adjustments has a lower cost-effectiveness (CE) ratio and a higher cost-benefit (CB) ratio, making it a more favorable measure for controlling NPS pollution in the HID.

The difference between tire wear particles and polyethylene microplastics in stormwater filtration systems: Perspectives from aging process, conventional pollutants removal and microbial communities

Tire wear particles (TWPs) in stormwater runoff have been widely detected and were generally classified into microplastics (MPs). TWPs and conventional MPs can be intercepted and accumulated in stormwater filtration systems, but their impacts on filtration, adsorption and microbial degradation processes of conventional pollutants (organic matters, nitrate and ammonium) have not been clarified. TWPs are different from MPs in surface feature, chemical components, adsorption ability and leaching of additives, which might lead to their different impacts on conventional pollutants removal. In this study, five different levels of aged polyethylene MPs (PEMPs) and aged TWPs contamination in stormwater filtration systems were simulated using thirty-three filtration columns. Results showed that ultraviolet aging treatment was less influential for the aging of TWPs than that of PEMPs, the specific surface area of aged PEMPs (1.603 m2/g) was over two times of unaged TWPs (0.728 m2/g) in the same size. Aged PEMPs and aged TWPs had different impacts on conventional pollutants removal performance and microbial communities, and the difference might be enlarged with exposure duration. The intensified aged PEMPs contamination generally promoted conventional pollutants removal, whereas aged TWPs showed an opposite trend. Mild contamination (0.01% and 0.1%, wt%) of aged PEMP/TWPs was beneficial to the richness and diversity of microbial communities, whereas higher contamination of aged PEMPs/TWPs was harmful. Aged PEMPs and TWPs had different impact on microbial community structure. Overall, the study found that TWPs were more detrimental than PEMPs in filtration systems. The research underscores the need for more comprehensive investigation into the occurrence, effects and management strategies of TWPs, as well as the importance of distinguishing between TWPs and MPs in future studies.

Influence of rubber particle inputs on nitrogen removal efficiency of bioretention systems

Bioretention systems effectively capture rubber particles and other microplastics in stormwater runoff. However, it is uncertain whether long-term particle accumulation affects pollutant removal efficacy. This study investigated the impact of various concentrations of ethylene-propylene-diene-monomer (EPDM) particles (0, 50, 100, and 400 mg/L) on bioretention system nitrogen removal performance. The input of EPDM during short-duration (2 h) rainfall favored the removal of nitrogen, and the total nitrogen effluent concentration of the bioretention system with EPDM was reduced by 0.59-1.52 mg/L compared with that of the system without EPDM. In addition, the input of EPDM reduced the negative effects of drought. During long-duration (24 h) rainfall, higher concentrations of EPDM led to lower nitrate-nitrogen concentrations in the effluent. The bioretention system with EPDM required less time for nitrate-nitrogen removal to reach 50% than that without EPDM input. Microbial community analysis showed that EPDM increased the relative total abundance of denitrifying bacteria (such as Dechloromonas, Zoogloea, Ramlibacter, and Aeromonas) by 7.25-10.26%, which improved the denitrification capacity of the system.

Evaluation of agricultural non-point source pollution infiltration on clogging and nitrogen leaching effects in BRCs with different plants in dryland areas

As high-standard farmland rapidly expands, agricultural non-point source pollution has emerged as a main environmental issue in China. To tackle nitrogen pollution, green infrastructure (GI), especially bioretention cells (BRCs), has been extensively adopted. However, the long-term effectiveness of these systems may be hindered by clogging and nitrogen leaching. In this study, we designed three BRCs simulation devices to investigate the effects of different plants on the removal of TSS TN and NO3-N from runoff through simulated pollutant infiltration experiments. To address this issue, laboratory research has explored the contributions of woody plants like Buxus and herbaceous plants such as Ophiopogon in BRCs, concentrating on their impact on system clogging and nitrogen leaching. The results indicated that, although the total suspended solids (TSS) removal rates in the Buxus and Ophiopogon treatment groups were slightly lower than in the control group, permeability experienced a notable enhancement, with the Buxus group showing a 24.47% increase in permeability. The removal rates of TN and NO3-N in the Buxus group were significantly reduced, decreasing by 31.82% and 41.25%, respectively, in comparison to the control group. After five months, Ophiopogon demonstrated considerably better root growth, with its root length, volume, and surface area all significantly exceeding those of the Buxus group. The choice of plants significantly influenced nitrogen cycling and system clogging, with the reduced removal rates in the Buxus group potentially linked to its weaker root system, lower abundance of actinomycetes, and reduced soil enzyme activity.

Nitrogen removal performance of bioretention cells under freeze-thaw cycles: Effects of filler structure and microbial community

Cold climates have an adverse effect on the nitrogen-removal capacity of bioretention cells, especially during freeze-thaw cycles (FTCs). To explore the effects of FTCs on the nitrogen removal performance of bioretention cells, this research compared the effects of FTCs on the pore structure and microbial community composition of the filler, and analyzed the nitrogen removal performance of the bioretention cell before (RT), during (FTC) and after (RRT) FTCs. The results demonstrated that RRT filler had a much greater number of pores with equivalent diameter <500 μm than RT filler, and that RRT had a higher pore volume and pore density than RT. Microbial community analysis revealed that the diversity and richness of the microbial community in FTC were lower than in RT, and the relative abundance of Lacunisphaera, Pseudomonas, and Dokdonella decreased significantly. There was no significant difference in microbial community richness between RRT and RT, however RRT diversity was lower. RRT has a higher relative abundance of nitrifying bacteria (Subgroup_10, Bryobacter, etc.) than RT, but a lower relative abundance of denitrifying bacteria (Pseudomonas, Dokdonella, Arenimonas, etc.). The nitrogen removal efficiency of FTC was inhibited, resulting in a decrease of 13.0 ± 4.86%, 19.7 ± 9.17%, and 26.6 ± 1.74% in the removal rates of ammonia nitrogen(NH4+-N), nitrate nitrogen(NO3--N), and total nitrogen(TN) when compared to RT, respectively. RRT improved nitrification and increased NH4+-N removal rate by 10.3 ± 2.69% compared to RT. However, because of denitrification inhibition, the nitrogen removal performance of RRT was not able to reach RT levels, and its NO3--N and TN removal rates decreased by 100 ± 4.70% and 58.3 ± 3.71%, respectively. This study has demonstrated that FTCs can permanently harm the bioretention cell's filler structure and microbial community, resulting in a significant decrease in the nitrogen removal performance of the bioretention cell designed according to warm climate conditions after experiencing FTCs.

Migration of naphthalene in a biochar-amended bioretention facility based on HYDRUS-1D analysis

Biochar has been proved as a promising and efficient filler in bioretention facilities for enhancing the stormwater pollutants removal. However, the migration behaviors of stormwater pollutants in biochar filled bioretention facilities is unclear. In this study, as one of the most typical stormwater pollutants, naphthalene was selected as an example and a HYDRUS-1D model was first used to understand the migration behavior of naphthalene in a bioretention facility. In comparison with the conventional bioretention soil media (sandy loam), the amended biochar filled bioretention cell showed that the naphthalene removal rate was enhanced by up to 10.1%. Meanwhile, the experimental data was well-fitted by the "two-site sorption model" in HYDRUS-1D model. Another, the effect of rainfall intensity on the naphthalene migration in both bioretention columns was further investigated. The HYDRUS-1D model fitting indicated that the increase in rainfall intensity promoted naphthalene migration by increasing hydraulic conductivity and water flux. In addition, static batch experiments revealed that the biochar filled fillers achieved about 50% higher adsorption capacity than sandy loam. The sensitivity analysis from the HYDRUS-1D model data verified adsorption coefficient Kd and longitudinal dispersivity λ are the main factors affecting naphthalene migration. Finally, the model simulation displays that the proportion of naphthalene retained by the fillers was highest during high rainfall intensities, indicating that the fillers remain the most important fate for naphthalene. This study presents research on the behavior and mechanisms of stormwater pollutant transport through improved bioretention facilities.

Elucidating biogeochemical characterization of nitrogen in the vadose zone integrating geochemistry, microorganism, and numerical simulation

A thorough comprehension of nitrogen biogeochemical processes in the vadose zone is crucial for the effective prevention and remediation of soil-groundwater system contamination. Despite the growing research on this subject, the full scope of nitrogen biogeochemical characterization in different geological environments remains poorly understood. This study addresses this knowledge gap by integrating geochemical, microbiological and numerical simulation approaches to gain a deeper insight into nitrogen biogeochemistry in agriculture. Our findings indicate the biogeochemical behavior of nitrogen in the vadose zone is mediated by microorganisms, driven by hydraulics, influenced by geological conditions and environmental factors. Along the groundwater flow, NH4+-N was found to be heavily accumulated in the topsoil of 0-40 cm, while NO3--N was transported and driven by hydrodynamics from both vertical and horizontal directions. Microbial diversity, species composition and functional microorganisms were significantly influenced by soil depth, rather than geomorphological types. Oxidation-reduction potential (ORP), total organic carbon (TOC), soil moisture (MOI), bicarbonate (HCO3-), and ferrous (Fe2+) were identified as the principal environmental factors that regulate nitrogen metabolism and the dominant biochemical processes, encompassing nitrogen fixation, nitrification, and denitrification. Driven by hydrodynamics, NH4+-N, NO2--N and NO3--N tend to form distinct biochemical reaction zones in the vertical vadose zone. These areas are dynamic and subject to geomorphologies. It should be noted that NO3--N can migrate towards groundwater from the clayey sand in the Alluvial Plain, which presents a potential risk of groundwater contamination. The fissure structure of loess may serve as the major transport pathway for groundwater nitrogen contamination in the Loess Tableland. This finding highlights the importance of integrating microbiology, geochemistry and hydraulics to elucidate the biogeochemical processes of nitrogen in the vadose zone with a dynamic mindset.

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.

Enhancing bioretention efficiency for pollutant mitigation in stormwater runoff: Exploring ecosystem cycling dynamics amidst temporal variability

In this study, three distinct bioretention setups incorporating fillers, plants, and earthworms were established to evaluate the operational efficiency under an ecosystem concept across varying time scales. The results revealed that under short-term operating conditions, extending the drying period led to a notable increase in the removal of NO3--N, total phosphorus (TP), and chemical oxygen demand (COD) by 5 %-7%, 4 %-12 %, and 5 %-10 %, respectively. Conversely, under long-time operating conditions, the introduction of plants resulted in a significant boost in COD removal by 10 %-20 %, while the inclusion of earthworms improved NH4+-N and NO3--N removal, especially TP removal by 9 %-16 %. Microbial community analysis further indicated the favorable impact of the bioretention system on biological nitrogen and phosphorus metabolism, particularly with the incorporation of plants and earthworms. This study provides a reference for the operational performance of bioretention systems on different time scales.

Deciphering linkages between DON and the microbial community for nitrogen removal using two green sorption media in a surface water filtration system

The presence of dissolved organic nitrogen (DON) in stormwater treatment processes is a continuous challenge because of the intertwined nature of its decomposition, bioavailability, and biodegradability and its unclear molecular characteristics. In this paper, 21 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in combination with quantitative polymerase chain reaction was applied to elucidate the molecular change of DON and microbial population dynamics in a field-scale water filtration system filled with two specialty adsorbents for comparison in South Florida where the dry and wet seasons are distinctive annually. The adsorbents included CPS (clay-perlite and sand sorption media) and ZIPGEM (zero-valent iron and perlite-based green environmental media). Our study revealed that seasonal effects can significantly influence the dynamic characteristics and biodegradability of DON. The microbial population density in the filter beds indicated that three microbial species in the nitrogen cycle were particularly thrived for denitrification, dissimilatory nitrate reduction to ammonium, and anaerobic ammonium oxidation via competition and commensalism relationships during the wet season. Also, there was a decrease in the compositional complexity and molecular weight of the DON groups (CnHmOpN1, CnHmOpN2, CnHmOpN3, and CnHmOpN4), revealed by the 21 T FT-ICR MS bioassay, driven by a microbial population quantified by polymerase chain reaction from the dry to the wet season. These findings indirectly corroborate the assumption that the metabolism of microorganisms is much more vigorous in the wet season. The results affirm that the sustainable materials (CPS and ZIPGEM) can sustain nitrogen removal intermittently by providing a suitable living environment in which the metabolism of microbial species can be cultivated and enhanced to facilitate physico-chemical nitrogen removal across the two types of green sorption media.

Unveiling the dynamic of nitrogen through migration and transformation patterns in the groundwater level fluctuation zone of a different hyporheic zone sediment

This study investigates the impact of water levels and soil texture on the migration and transformation of nitrate (NO3--N) and ammonium (NH4+-N) within a soil column. The concentrations of NO3--N gradually decreased from an initial concentration of 34.19 ± 0.86 mg/L to 14.33 ± 0.77 mg/L on day 70, exhibiting fluctuations and migration influenced by water levels and soil texture. Higher water levels were associated with decreased NO3--N concentrations, while lower water levels resulted in increased concentrations. The retention and absorption capacity for NO3--N were highest in fine sand soil, followed by medium sand and coarse sand, highlighting the significance of soil texture in nitrate movement and retention. The analysis of variance (ANOVA) confirmed statistically significant variations in pH, dissolve oxygen and oxidation-reduction potential across the soil columns (p < 0.05). Fluctuating water levels influenced the migration and transformation of NO3--N, with distinct patterns observed in different soil textures. Water level fluctuations also impacted the migration and transformation of NH4+-N, with higher water levels associated with increased concentrations and lower water levels resulting in decreased concentrations. Among the soil types considered, medium sand exhibited the highest absorption capacity for NH4+-N. These findings underscore the significant roles of water levels, soil texture, and soil type in the migration, transformation, and absorption of nitrogen compounds within soil columns. The results contribute to a better understanding of nitrogen dynamics under varying water levels and environmental conditions, providing valuable insights into the patterns of nitrogen migration and transformation in small-scale soil column experiments.

Characteristics of nitrogen distribution and its response to microecosystem changes in green infrastructure with different woody plants

With the acceleration of urbanization, N pollution in rainfall runoff has become the primary cause of eutrophication. In order to control N pollution in rainfall runoff, green infrastructure (GI) has been widely implemented. However, little is known about the process through which plants, especially woody plants, affect N distribution and the microecosystem in GI. Limited information suggests that woody plants mainly affect N distribution and alter the microecosystem through the influence of their roots. Therefore, laboratory tests were conducted to investigate the roles of the taproot plant Sophora japonica and the fibrous root plant Malus baccata and the resultant changes at the microecosystem level regarding N removal in a column-scale GI. After one year of growth, analysis of the morphological traits of the roots revealed that the average root length and diameter of S. japonica were approximately 2.3 and 1.8 times greater than those of M. baccata, respectively. An investigation of microbial diversity revealed that in comparison to the control GI system without plants, the GI systems with S. japonica and M. baccata hosted 45.68% and 59.88% more Actinobacteria, respectively. Further, the soil urease (S-UE) activities in the GI systems with S. japonica and M. baccata were 13.6% and 98.8% higher than that in the control, respectively, and the soil acid protease (S-ALPT) activities were 20.5% and 25.4% higher than that in the control, respectively. Compared to the control and the S. japonica GI system, the NH₃-N content in the soil of the M. baccata GI was 94.4% and 15.2% lower, respectively, and the NO₃-N content was 57.3% and 12.7% lower, respectively. The M. baccata GI system had the lowest NH₃-N and NO₃-N contents because it was most abundant in Actinobacteria and Arthrobacter and had the highest S-UE and S-ALPT activities. The results may be useful for improving N removal in GI containing different woody plants, and by extension for improving control of N pollution from rainfall runoff.

Evaluation of nitrogen removal, functional gene abundance and microbial community structure in a stormwater detention basin

Stormwater control measures such as detention basins are used to mitigate the negative effects of urban stormwater resulting from watershed development. In this study, the performance of a detention basin in mitigating nitrogen pollution was examined and the abundance of N-cycling genes (amoA, nirK, nosZ, hzsB and Ntsp-amoA) present in the soil media of the basin was measured using quantitative PCR. Results showed a net export of nitrogen from the basin, however, differences between in- and outflow concentrations were not significant. Furthermore, the quantitative PCR showed that nirK (denitrification gene) was more abundant in the winter season, whereas amoA (nitrification gene) was more abundant in the summer season. The abundance of nirK, Ntsp-amoA and hzsB genes also varied with the sampling depth of soil and based on 16S rRNA gene sequencing of soil samples, Actinobacteria and Proteobacteria were the most dominant phyla. Species diversity appeared higher in summer, while the top and bottom layer of soil clustered separately based on the bacterial community structure. These results underline the importance of understanding nitrogen dynamics and microbial processes within stormwater control measures to enhance their design and performance.