Mechanisms of propeller jet-induced migration, release, and distribution of perfluoroalkyl acids in sediment-water systems

Release of PAHs from sediments to seawater under wave: Indoor microcosms and level IV fugacity models

Estuaries and coasts are located at the land-sea interface, where sediment liquefaction due to strong wave action results in significant material exchange at the sediment-seawater system. Polycyclic aromatic hydrocarbons (PAHs), as organic pollutants, are distributed across various media. Herein, the impact of wave was studied on the release of PAHs through indoor microcosmic experiments combined with a level IV fugacity model. Comparison revealed that the release amount and rate of PAHs during static consolidation stage were minimal, whereas wave action substantially enhanced the release. Particularly the sediments in a liquefied state, the PAHs release in Stage III was 1.55-1.86 times that in Stage II, reaching 84.73 μg/L. The loss of soil strength and strong hydrodynamic effects resulted in a substantial release of PAHs into seawater along with suspended solids. Due to volatility of 2-ring PAHs and difficult desorption of 6-ring PAHs, 3-5-ring PAHs are the main contributors to releases into seawater. The model results also indicated that the three PAHs had different fates in the sediment-seawater system, with sediment serving as an important "reservoir" for benzo[a]pyrene entering seawater, while functioning as both a "sink" and a "source" for pyrene.

Intense Turbulent Bursts Promote the Release of Perfluoroalkyl Acids from Sediments at High Flow Velocity

Despite frequent detection of high levels of perfluoroalkyl acids (PFAAs) in sediments, research on the environmental fate of PFAAs in sediments, particularly under hydrodynamic conditions, is rather limited, challenging effective management of PFAA loadings. Therefore, this study investigated the release and transport of 15 PFAAs in sediments under environmentally relevant flow velocities using recirculating flumes and revealed the underlying release mechanisms by identifying related momentum transfer. An increased velocity enhanced the release magnitude of total PFAAs by a factor of 3.09. The release capacity of short-chain PFAAs was notably higher than that of long-chain PFAAs, and this pattern was further amplified by flow velocity. Pore-water drainage was the major pathway for PFAA release, with the release amount predominantly determined by flow velocity-induced release intensity and depth, as well as affected by the perfluorocarbon chain length and sediment size. The weak anion exchanger-diffusion gradients in the thin-film technique confirmed that the release depth of PFAAs increased with flow velocity. Quadrant analysis revealed that the rise in the frequency and intensity of turbulent bursts driven by sweeps and ejections at high flow velocity was the underlying cause of the increased release magnitude and depth of PFAAs.

Can on-site leachate treatment facilities effectively address the issue of perfluoroalkyl acids (PFAAs) in leachate?

In recent decades, the presence of perfluoroalkyl acids (PFAAs) in municipal solid waste leachate has emerged as a growing concern. Research has focused on PFAA release and occurrence characteristics in landfill and waste-to-energy leachate, highlighting their significant impact when released into wastewater treatment plants. Given the extremely high loading rate faced by current on-site leachate treatment plants (LTPs), the objective of this study is to assess whether the current "anaerobic/aerobic (A/O) + membrane bioreactor (MBR) + nanofiltration (NF) + reverse osmosis (RO)" configuration is effective in PFAAs removal. Concentrations of raw and treated leachate in 10 on-site LTPs with same treatment configuration and varying landfill ages were measured, and a comprehensive mass flow analysis of each treatment process was conducted. The results indicate that A/O treatment has limited capacity for PFAA removal, while NF and RO processes reached 77.44 % and 94.30 % removal rates of ∑PFAAs concentration, respectively. Short-chain PFAAs (> 80 % detected frequency) primarily influenced the distribution and variations of PFAAs in leachate and tend to disperse in the water phase. Correlation analysis revealed the current on-site LTPs exhibit a more efficient removal capacity for long-chain PFAAs.

Release of perfluoroalkyl acids from sediments under the effects of the discharge ratio and flow flux at a Y-shaped confluence

The sediments in riverine environments contain notably high concentrations of perfluoroalkyl acids (PFAAs), which may be released into the water body under different hydrodynamic forces, such as those occurring at Y-shaped confluences. The release of PFAAs may pose a significant risk to the surrounding aquatic ecosystems. However, our understanding of the release and transport of PFAAs from sediments at Y-shaped confluences remains unclear. Thus, in this study, we performed a series of flume experiments to explore the effects of discharge ratio and total flow flux on the release and redistribution of PFAAs. The results indicated that these two parameters significantly affected the hydrodynamic features of confluences and the water physicochemical parameters. PFAA concentrations in the dissolved phase and suspended particulate matter (SPM) rose significantly as the discharge ratio and total flow flux increased. The dissolved phase was the predominant loading form of PFAAs, with short-chain PFAAs being the main kind, while long-chain PFAAs were dominant in the SPM. The spatial distribution pattern of PFAAs in sediments at the confluence exhibited a high degree of correspondence with hydrodynamic zones. The separation zone and maximum velocity zone were consistent with sediment regions with low and high capacities to release PFAAs, respectively. The patterns of variation in PFAA distribution were comparable to those observed in hydrodynamic zones as the discharge ratio and total flow flux varied. Furthermore, these two parameters altered the partitioning behaviors of PFAAs; specifically, the PFAAs in sediments tended to be released into the pore-water, while the liberated PFAAs tended to attach to SPM. Linear regression and correlation analyses suggested that the stream-wise and vertical flow velocity components near the sediment-water interface were the primary contributors to sediment suspension and PFAA exchange between the water column and pore-water. These findings will help us to understand the patterns of PFAA release in sediments at Y-shaped confluences and assist in the management of PFAA-contaminated sediments at these locations.

Field study on endogenous perfluoroalkyl acid release and their spatiotemporal distribution processes induced by inland navigation

Dense populations and industries in regions with developed inland waterways have caused the significant discharge of perfluoroalkyl acids (PFAAs) into surrounding waterways. Despite being the dominant energy input in the waterways, the impact of ship navigation on endogenous PFAA release is unclear. In this study, a field experiment was carried out in the Wangyu River (Taihu Basin, China) to investigate the spatiotemporal distribution processes of PFAAs in the water column after passage of ships with different tonnages, speeds, and draughts. The results showed that the PFAA contents did not decrease continuously with time but increased with a lag after the passing ship triggered a transient massive dissolution of PFAAs into the overlying water. In addition, PFAA contents in suspended particulate matter (SPM) exhibited a fluctuating downward trends after their peak at the moment of ship passage. Vertically, the PFAA concentrations among the layers of overlying water were relatively homogeneous, whereas SPM exhibited substantial heterogeneity in its distribution and adsorption of PFAAs. Moreover, the differences in jet scouring velocity (u), disturbance duration (t), and draught (h) of ships resulted in large variability in PFAA contents in the water column. Variance partitioning analysis further quantified the effects of u, t, and h on total PFAAs in the water column, with individual contributions of 53 %, 12 %, and 6 %, respectively. Furthermore, the release of endogenous PFAAs induced by ship passage involved rapid and slow processes, the former determining the overall PFAA release and the latter affecting PFAA concentration recovery in the water column. The findings provide in-situ observational data on spatiotemporal variations of PFAAs in multiphase media following ship passage, enhancing our understanding of endogenous pollution in inland waterways.