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Because of the difficulty of specifying optimal design parameters of rectangular sedimentation tanks using a forward numerical model, an inverse calculation model based on an optimization algorithm and a forward model were developed in this paper. Using this model, a numerical simulation of the sedimentation tank involving determination of the velocity field and the concentration distribution of the particles by the forward model was conducted. The eddy viscosity was obtained with the aid of turbulence model equations. The inverse model was applied to the optimal design of the horizontal baffle location in a given sedimentation tank. As a one-dimensional nonlinear optimization method, Brent's method was used. Moreover, the effect of the horizontal baffle location on flow and solids removal ratio was also discussed. Compared with the traditional forward model for specifying optimal design parameters for rectangular sedimentation tanks, the inverse calculation model can search directly for the optimum design parameters and can obtain good results. [ABSTRACT FROM AUTHOR]

• Discharge ratio and total flow flux significantly enhanced the release of PFASs. • The dissolved phase was the predominant loading form of released PFASs. • Short-chain PFASs dominated in the dissolved phase, while long-chain PFASs in SPM. • Distribution patterns of PFASs highly corresponded to the hydrodynamic zones. • Stream-wise and vertical flow velocities near the SWI were crucial to PFASs release. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Shorter-chain PFAAs show pH- and ionic strength-dependent sorption on AC. • DOM competes with longer-chain PFAAs but increases shorter-chain one sorption. • AC displays long-term and superior performance in immobilizing sediment PFAAs. • AC significantly reduced 45.5%–99.2% PFAA release under various disturbances. • After intense disturbance stopped, water PFAAs fell to initial levels or lower. The detection of elevated levels of perfluoroalkyl acids (PFAAs) in sediments has become a significant concern, urgently requiring management and remediation efforts. In this study, we investigated the effectiveness of industrially cost-effective activated carbon (AC) in remediating PFAA-contaminated sediments at different disturbance intensities and explored the sorption capacity of AC under broad environmentally relevant conditions and in response to environmental variations. AC exhibited high sorption effectiveness for PFAAs (excluding perfluorobutanoic acid < 40 %) across different pH, ionic strengths (IS), and dissolved organic matter (DOM). However, the increase in pH or reduction in IS might reactivate partially immobilized PFAAs. DOM outcompeted longer-chain PFAAs for sorption sites, resulting in their reactivation on AC, while it showed a stronger sorption than a competitive effect on shorter-chain PFAAs. The 192-day remediation experiment showed that AC significantly deactivated mobile PFAAs and decreased PFAA release by 45.5 %–99.2 % and 61.0 %–98.8 % under weak and intense disturbances, respectively, when compared with untreated sediment. Although intense disturbance led to an increase in PFAA release, the PFAA levels in the water column of the AC group after intense disturbance were comparable or even lower than those before intense disturbance, primarily owing to the secondary sorption of suspended AC. These findings are crucial for the appropriate and safe use of AC for PFAA sequestration, the management of PFAA-contaminated sediments, and the development of effective sediment remediation strategies. [ABSTRACT FROM AUTHOR]

Pollution source identification is vital in water safety management. An integrated simulation-optimization modelling framework comprising a process-based hydrodynamic water quality model, artificial neural network surrogate model and particle swarm optimization (PSO) was proposed to achieve rapid, accurate and reliable pollution source identification. In this study, the hydrodynamics and water quality processes in a straight lab-based flume were simulated to test pollution source identification under steady flow conditions. Additionally, the pollution source identification in the unsteady flow conditions was examined using a real-life estuary, specifically the Yangtze River estuary. First, we developed two process-based models to simulate hydrodynamics and water quality in the flume and estuary. Then, the data generated from the process-based models were used to develop surrogate models. Three typical artificial neural networks (ANNs) algorithms: backpropagation (BP), radial basis function (RBF) and general regression neural networks (GRNN) were selected to develop surrogates for process-based models (PBMs), and they were coupled with PSO algorithm to achieve the hybrid modelling framework for pollution source identification. Our results showed that hybrid PBM-ANNs-PSO models could be applied to identify the pollution source and quantify release intensity in spatial distribution when the discharge type was assumed as the point source with a continuous release. Multiple-performance criteria metrics, in terms of the coefficient of determination, root-mean-square error, mean absolute error, evaluated the model performance as "Excellent prediction". The BP-PSO models consistently appear to be the top-performing source identification model within the developed models, with most cases of relative error (RE) values lower than 5%. The new insights from the hybrid modelling framework would provide useful information for the local government agency to make reasonable decisions regarding pollution source identification issues. [Display omitted] • The modelling framework was developed to identify the multiple pollution sources in surface water. • The modelling framework was tested in both flume and estuary cases. • Backpropagation models outperform other models within the tested surrogate models. • Population size of 15–25 was found suitable for particle swarm optimization in tested cases. [ABSTRACT FROM AUTHOR]

Turbulence generated within the vegetated confluence system is important for water quality and river management. In this study, we conducted a series of experiments to explore the extent to which emergent rigid vegetation in the confluence channel influences hydrodynamic characteristics and contaminant transport. First, a series of tests with increasing discharge ratios (from 0.35, 0.5, and 1) was conducted to quantify the effects of the discharge ratio on hydrodynamic conditions within the vegetated confluence. Then, tests with different discharge ratios were also set up to explore how contaminants released locations and modes (line and point source) influence the transport and mixing of contaminants. The results showed that increasing the discharge ratio induced larger momentum in the confluence area. The increase in discharge ratio rendered the circulation stronger, and its position came earlier in the non-vegetative area. In addition, the dimensionless turbulent kinetic energy peaked near the interface of the non/vegetated zone. With the increase in the discharge ratio, the dimensionless turbulent kinetic energy was found to be smaller. In the contaminants transport tests, the results revealed larger discharge ratio could speed up contaminants transport and mixing. The applications from this study would be helpful to pollutant transport management in natural confluences. • The effects of discharge ratios on vegetated flow at confluence were quantified. • Velocity profile, secondary flow and longitudinal dispersion coefficient were presented. • Contaminants released by line and point sources were considered in the experiments. • Increasing discharge ratios speed up contaminants' transport and mixing. [ABSTRACT FROM AUTHOR]

The freshwater resources deficient has been dominated the world's science and policy agenda, owing to the population growth, rapid industrialization, and environmental pollution. Spray evaporator, as a promising and high-efficient desalination technology, has been widely applied to desalination or high salinity wastewater treatment industries. However, current studies on the evaporation characteristics of spray evaporator lack comprehensive analysis and further parameter screening that causes the difficulty to effectively choose optimal parameters for optimization. Therefore, the influences of 11 parameters on evaporation performance were systemically studied via computational fluid dynamics, evaluated via evaporation efficiency, a single droplet evaporation time, and atomization effect, and eventually, the most influential parameters were screened out via stepwise multiple linear regression. The results indicated that all parameters influence the evaporation performance, but the hot air temperature and velocity are the most influential parameters affecting the evaporation efficiency that can jointly explain 55.8 %–58.7 % variations and characteristics of evaporation and should be preferentially considered to improve the efficiency. Furthermore, the compressed air pressure is also worth considering since it could enhance evaporation performance and atomization effect simultaneously. This study provides a new insight and understanding for the design and optimization of spray evaporator. [Display omitted] • The parameter optimization of spray evaporator was comprehensively examined via CFD. • Stepwise multiple linear regression screens out the most influential parameters. • Hot air velocity and temperature are the most key factor for evaporation performance. • Nozzle number and compressed air pressure significantly influence the atomization. [ABSTRACT FROM AUTHOR]

Constructed wetlands (CWs) are often used to treat wastewater discharged from wastewater treatment plants (WWTPs), while emerging contaminants (such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)) have been commonly discovered in WWTPs. However, no research has examined whether PFOA/OS (i.e. PFOA and PFOS) affects the performance of CW. Therefore, this study compared the nutrient removal efficiencies of four CWs with varied configurations under PFOA/OS and no PFOA/OS stress conditions. We found that CW containing plants or/and iron-carbon had higher removal efficiency for nutrients (except NH 4 +–N) than conventional CW in stable operation under wastewater without PFOA/OS. Plants or/and iron increased the nutrient removal efficiency by plant uptake, chemical reaction, and co-precipitation of iron hydroxides. In contrast, the iron-carbon inhibited the nitrification of nitrifying bacteria by consuming dissolved oxygen, converting NO 3 −–N to NH 4 +–N. Although the removal efficiencies of nutrients by CWs differed after introducing PFOA/OS, the removal order was consistent with those before adding PFOA/OS. Plants or/and iron-carbon effectively increased CWs' resistance to PFOA/OS loading and toxicity, and the function of iron-carbon was superior to the plants. In addition, PFOA/OS reduced the abundances of microbes Hydrogenophaga , Pseudomonas , Sphingomonas , Nitrospira , and Candidatus_Accumulibacter that contributed to nutrient removal. [Display omitted] • Additions of iron-carbon increased the nutrient removal excepting NH 4 + − N. • The presence of PFOA/OS inhibited the nutrients removal efficiencies. • Iron-carbon improved the tolerance of CW to PFOA/OS loading and toxicity. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl acid (PFAA) exposure poses a potential hazard to wildlife and humans. Food consumption is one of the main routes of PFAA exposure for the general population, with aquatic organisms being the major contributors. To evaluate the risk of coastal residents' intake of wild aquatic organisms, 14 PFAAs were detected in crucian carp and oriental river prawn from 18 sampling sites from the lower reaches of Yangtze River. The total PFAA (∑PFAA) concentrations ranged from 5.9 to 51.3 ng/g wet weight (ww) in the muscle of crucian carp and river prawn, suggesting the potential risk to human and wildlife. Perfluorooctanesulfonate (PFOS), perfluorooctanoic acid (PFOA) and long-chain PFAAs (C ≥ 10) were the main pollutants in the tissues of crucian carp and river prawn, which are known for their higher bioaccumulation capacity. The ∑PFAA concentration in all the samples showed an increasing trend from upstream to downstream and was higher in the south bank, owing to population density, prevailing winds, background pollution and industrial emission. Principal component analysis-multiple linear regression and Pearson correlation analysis showed that WWTP effluent, industrial pollution and surface runoff ware the main sources of PFAAs in the aquatic organisms and industrial pollution highest contributor, suggesting better regulation is needed to manage them. The assessment of risk to human health and wild life suggested a low risk for most residents of cities along the Yangtze River except for resident of Nantong, where frequent consumption of wild aquatic organisms may cause potential risk to human health, especially for traditional eaters and middle-aged people. • PFAAs were monitored in fish and shrimp along the lower Yangtze River, China. • ∑PFAA ranged from 5.9 to 51.3 ng/g in the muscle of fish and shrimp. • PFAA were higher downstream and near the southern shore, linked with mixed reasons. • Industrial pollution was the main potential source of PFAAs in aquatic products. [ABSTRACT FROM AUTHOR]