Migration and adsorption of naphthalene in road-deposited sediments from stormwater runoff: Impact of the particle size

The accumulation process of pollutants in deposited particles of different sizes on different roads in Beijing, China

Road-Deposited Sediments (RDS) samples were collected from four different roads in Beijing, and the distribution of pollutants in RDS with various particle sizes was compared. In this study, the cumulative mass of RDS exhibited a positive correlation with the number of dry days, and the RDS load below 75 μm was also influenced by road traffic volume. As traffic volume escalated, there was a corresponding increase in the load of these smaller RDS. Most pollutants accumulated within RDS with sizes below 150 μm, rendering them the primary contributors to the pollution. In terms of the antecedent dry-weather days, fifteen days emerged as a potentially pivotal point, with both the rate of pollutant accumulation and the contribution of pollution sources to RDS having stabilized after this duration. The origins of pollutants in roads of different functional areas exhibited certain disparities. The pollutants on major roads with high traffic volume were attributed to frequent vehicular activities. The pollutants on residential roads stemmed from soil particles and fallen leaves in the roadside green belts as well as from human activities. And the pollutants on urban-rural crossroad might be attributed to the industrial contamination with factories located on one side.

DC Electric Fields Promote Biodegradation of Waterborne Naphthalene in Biofilter Systems

Biofiltration is a simple and low-cost method for the cleanup of contaminated water. However, the reduced availability of dissolved chemicals to surface-attached degrader bacteria may limit its efficient use at certain hydraulic loadings. When a direct current (DC) electric field is applied to an immersed packed bed, it invokes electrokinetic processes, such as electroosmotic water flow (EOF). EOF is a surface-charge-induced plug-flow-shaped movement of pore fluids. It acts at a nanometer distance above surfaces and allows the change of microscale pressure-driven flow profiles and, hence, the availability of dissolved contaminants to microbial degraders. In laboratory percolation columns, we assessed the effects of a weak DC electric field (E = 0.5 V·cm-1) on the biodegradation of waterborne naphthalene (NAH) by surface-attached Pseudomonas fluorescens LP6a. To vary NAH bioavailability, we used different NAH concentrations (C0 = 2.7, 5.1, or 7.8 × 10-5 mol·L-1) and Darcy velocities typical for biofiltration (U ¯ = 0.2-1.2 × 10-4 m·s-1). In DC-free controls, we observed higher specific degradation rates (qc) at higher NAH concentrations. The qc depended on U ¯ , suggesting bioavailability restrictions depending on the hydraulic residence times. DC fields consistently increased qc and resulted in linearly increasing benefits up to 55% with rising hydraulic loadings relative to controls. We explain these biodegradation benefits by EOF-altered microscale flow profiles allowing for better NAH provision to bacteria attached to the collectors even though the EOF was calculated to be 100-800 times smaller than bulk water flow. Our data suggest that electrokinetic approaches may give rise to future technical applications that allow regulating biodegradation, for example, in response to fluctuating hydraulic loadings.

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.

Investigation the existence and mechanism of Cu(II)-sulfamethoxazole co-pollution by road-deposited sediments in stormwater runoff

In recent years, the escalating attention on Pharmaceutical and Personal Care Products (PPCPs) and Heavy Metals in urban stormwater runoff highlights the critical role of Road-deposited sediments (RDS) as a significant carrier for pollutant occurrence and transport in runoff. However, existing research has overlooked the composite characteristics of PPCPs and Heavy Metals, hampering a holistic understanding of their transformation in diverse forms within runoff. This limitation impedes the exploration of their subsequent migration and conversion properties, thereby obstructing coordinated strategies for the control of co-pollution in runoff. This study focuses on the typical PPCP sulfamethoxazole (SMX) and heavy metal Cu(II) to analyze their occurrence characteristics in the Runoff-RDS system. Kinetics and isotherm studies reveal that RDS effectively accumulates SMX and Cu(II), with both exhibiting rapid association with RDS in the early stages of runoff. The accumulation of SMX and Cu(II) accounts for over 80 % and 70 % of the total accumulation within the first 240 min and 60 min, respectively. Moreover, as runoff pH values decrease, the initially synergistic effect between the co-pollutant transforms into an antagonistic effect. In the composite system, varying pH values from 2.0 to 6.0 lead to an increase in SMX accumulation from 4.01 mg/kg to 6.19 mg/kg and Cu(II) accumulation from 0.43 mg/g to 3.39 mg/g. Compared to the single system, the composite system capacity for SMX and Cu(II) increases by 0.04 mg/kg and 0.33 mg/g at pH 4.0. However, at pH 3.0, the composite system capacity for SMX and Cu(II) decreases by 0.21 mg/kg and 0.36 mg/g, respectively. Protonation/deprotonation of SMX under different pH conditions influences electrostatic repulsion/attraction between SMX and RDS. The mechanism of RDS accumulation of SMX involves Electron Donor-Acceptor (EDA) interaction, hydrogen bond interaction, and Lewis acid-base interaction. Cu(II) enrichment on RDS includes surface complexation reaction, electrostatic interaction, and surface precipitation. Complex formation enhances the accumulation of both SMX and Cu(II) on RDS in runoff. This study elucidates the co-occurrence characteristics and mechanisms of SMX and Cu(II) co-pollution in runoff systems. The findings contribute valuable insights to understanding the existence patterns and mechanisms of co-pollution, providing a reference for investigating the migration and fate of co-pollutant in runoff. Moreover, these insights could offer guidance for the development of effective strategies to mitigate co-pollution in rainwater.