Contamination Processes Research Articles

Removal of Inorganic Pollutants and Recovery of Nutrients from Wastewater Using Electrocoagulation: A Review

Water pollution is a major concern due to its detrimental effects on the environment and public health. The particular danger of inorganic pollutants arises from their persistent toxicity and inability to biodegrade. Recently, electrocoagulation (EC) has been demonstrated as an alternative sustainable approach to purifying wastewater due to the increasingly strict pollution prevention rules. In particular, EC has been used to remove inorganic pollutants, such as Cr, Zn, Pb, or As. EC has emerged as a sustainable tool for resource recovery of some inorganic pollutants such as N and P that, when recovered, have value as plant nutrients and are critical in a circular economy. These recovered materials can be obtained from diverse agricultural drainage water and recycled as fertilizers. In this work, a state-of-the-art technique is reviewed describing the advances in contaminant removal and nutrient recovery using EC through an in-depth discussion of the factors influencing the contaminant removal process, including operating pH, time, power, and concentration. Furthermore, limitations of the EC technology are reviewed, including the high-power consumption, fast deterioration of the sacrificial electrodes, and the types of contaminants that could not be efficiently removed. Finally, new emerging constructs in EC process optimization parameters are presented.

Surface cleaning with atmospheric pressure plasma jet investigated by in-situ optical emission spectroscopy and laser-induced breakdown spectroscopy

Cleaning of surfaces with atmospheric pressure plasma jet (APPJ) is investigated by in-situ optical emission spectroscopy (OES) and laser-induced breakdown spectroscopy (LIBS). The APPJ device operates a spark discharge of kW power in Argon gas flow resulting in a powerful plasma jet expanding into air. For cleaning experiments samples are coated with lubricant layers of 1.1 to 7.1 µm thickness. Light collected at the sample surface during APPJ treatment is analyzed spectroscopically and used to monitor the cleaning process. LIBS chemical imaging delivers spatial cleaning profiles of plasma treated surfaces. From measured emission intensities of CN molecular band and Na atomic line the cleaning efficiencies for carbon and Na containing contaminants are determined. The power of APPJ plasma generator, distance between sample and jet nozzle, scan speed, and Argon gas flow are varied to optimize the surface treatment. Thermal and non-thermal processes contribute to cleaning. For the carbon containing contaminant thermal processes are dominating (∼90 %) while also non-thermal processes (∼30–45 %) are relevant for the Na containing component. A cleaned surface area per time from 0.3 to 10 cm2/s is investigated. Cleaning efficiency up to 95 % is obtained highlighting the potential of APPJ surface cleaning under ambient conditions.

Temporal and spatial evolution of residual saltwater contamination in coastal subterranean reservoirs

This study numerically investigated the dynamic process of residual saltwater contamination in subterranean reservoirs (aquifer upstream of subsurface physical barrier) for the first time. The results indicated that the groundwater level elevation resulting from subsurface physical barriers induced a small hydraulic gradient in the subterranean reservoir, with residual saltwater convection driven by the density contrast between saltwater and freshwater. This led to persistent inland intrusion of residual saltwater, causing a gradual expansion of the contamination area (i.e., concentration higher than 0.25 g/L) and a decreased area of high-salinity zone. The area of low concentration residual saltwater (0.25 g/L) initially increased and then decreased over time. For large-scale aquifers, the proportion of the maximum contaminated area to the total aquifer area increased from 0.05 to 0.17. Subsequently, the low-concentration saltwater was considered as a relative high-concentration for ambient freshwater, which released salts into the surroundings and the contamination area reduced to 0.0003 at 160000 d. In small-scale aquifers, residual saltwater transport was affected by inland boundary, and the low-concentration saltwater reached inland boundary at approximately 2000 d, which limited its horizontal expansion and resulted in the polluted area reaching an inflection point early relative to large-scale aquifers. The salt transfer from high-concentration residual saltwater to low-concentration saltwater was closely related to aquifer parameters of hydraulic conductivity, dispersivity, and molecular diffusion coefficient. These findings suggest that residual saltwater contamination should not be overlooked when assessing the efficiency of subterranean reservoirs.

Ecological Risk Assessment to Aquatic Life from Metals in the Surface Sediments of the Santiago-Guadalajara River Basin, Mexico

ABSTRACT The Santiago-Guadalajara River (SGR) is one of the most polluted river systems in Mexico because there is still a significant amount of untreated industrial, agricultural and municipal wastewater discharged. A sediment monitoring campaign was carried out at 25 sampling points located in the Santiago and Zula rivers, as well as in their main tributaries. In this work, six indices and criteria were selected to assess the level of metal contamination in the main and tributary streams. The following sequence of metals of concern were identified (mean values in mg kg-1 dry basis): Zn (71.92)> Cu (35.22)> Cr (23.82) > Ni (14.95)> Pb (10.82) > As (2.82) > Cd (2.40) > Sb (2.06). Previous studies in the region agree that Al, Fe, Mn, and Ba are part of the natural lithologic composition of the basin, and what is found in the sediments is likely the result of the natural rock weathering processes rather than an anthropogenic contamination process. According to the proposed assess methods Cu, Cr, Ni, Pb, and Zn were found in low to moderate levels of contamination, and Sb and Cd were found in considerable to very high contamination levels in several of the monitored stations.

Geochemical and Sr-Nd isotopic implications for the petrogenesis of the late Silurian Shitoukengde mafic–ultramafic intrusion in the East Kunlun Orogen, NW China

The Shitoukengde mafic–ultramafic intrusion is the host of the second-largest sulfide deposit after the Xiarihamu Ni-Co deposit in the East Kunlun Orogenic Belt (EKOB), northern Tibet Plateau, China. Despite several studies, the age, petrogenesis, and the cause of low Ni-tenor for this intrusion remain poorly constrained. In this study, zircons separated from the pyroxenite at Shitoukengde yield a SHRIMP U-Pb age of 418.9 ± 3.1 Ma, corresponding to the widespread magmatism of the late Silurian to early Devonian in the EKOB. Whole-rock major and trace element compositions indicate that fractional crystallization played a key role in controlling the magma composition and element distribution within the intrusion. Mafic-ultramafic rocks of the intrusion, particularly peridotite, have highly variable and exceptionally elevated (87Sr/86Sr)i and negative ɛNd(t) values. Some samples from the Shitoukengde intrusion exhibit initial Sr-Nd isotope ratios that overlap with those from the Xiarihamu intrusion, while others (e.g., peridotite) display higher (87Sr/86Sr)i values than those observed in the latter. The unusual Sr-Nd isotopic compositions of the Shitoukengde intrusion could be attributed to the assimilation of Mg-rich carbonate within a deep-seated magma chamber. This contamination process facilitates the crystallization of olivine, consequently reducing Ni content in residual magma. Furthermore, the contamination of Mg-rich carbonate may promote oxygen fugacity and thus enhance the solubility of sulfur while restricting the sulfide saturation in the magma. We thus propose that the extensive contamination of Mg-rich carbonate is a key factor contributing to the relatively low Ni-tenor observed at Shitoukengde.

Exploring the microbe-mediated biological processes of BTEX and toxic metal(loid)s in aging petrochemical landfills

Aging petrochemical landfills serve as reservoirs of inorganic and organic contaminants, posing potential risks of contamination to the surrounding environment. Identifying the pollution characteristics and elucidating the translocation/ transformation processes of typical contaminants in aging petrochemical landfills are crucial yet challenging endeavors. In this study, we employed a combination of chemical analysis and microbial metagenomic technologies to investigate the pollution characteristics of benzene, toluene, ethylbenzene, and xylene (BTEX) as well as metal(loid)s in a representative aging landfill, surrounding soils, and underlying groundwater. Furthermore, we aimed to explore their transformations driven by microbial activity. Our findings revealed widespread distribution of metal(loid)s, including Cd, Ni, Cu, As, Mn, Pb, and Zn, in these environmental media, surpassing soil background values and posing potential ecological risks. Additionally, microbial processes were observed to contribute significantly to the degradation of BTEX compounds and the transformation of metal(loid)s in landfills and surrounding soils, with identified microbial communities and functions playing key roles. Notably, co-occurrence network analysis unveiled the coexistence of functional genes associated with BTEX degradation and metal(loid) transformation, driven primarily by As, Ni, and Cd. These results shed light on the co-selection of resistance traits against BTEX and metal(loid) contaminants in soil microbial consortia under co-contamination scenarios, supporting microbial adaptive evolution in aging petrochemical landfills. The insights gained from this study enhance our understanding of characteristic pollutants and microbial transformation processes in aging landfills, thereby facilitating improved landfill management and contamination remediation strategies.

Analytical solution for one-dimensional chemo-hydro-mechanical coupled consolidation under time-dependent loading in buffer clay layer

An analytical method is developed for solving the coupled chemo-hydro-mechanical consolidation in a clay buffer layer under time-dependent loading. The coupled governing equations for the chemo-hydro-mechanical process are established in the time and spatial domain first. Then the governing equations are decoupled into two partial differential equations by introducing two variables. The analytical solutions corresponding to ramp and exponential loadings are finally derived based on the initial and boundary conditions. The developed analytical solutions are verified via comparing with the numerical results simulated by COMSOL Multiphysics. Based on the developed solutions, selected parametric study is carried out to investigate the influence of major parameters and hydraulic boundary conditions on the contaminants transport and pore water pressure dissipation in buffer clay layer. The results show that the major parameters have effects on the generation and dissipation of pore pressure, while only effective coefficient of diffusion, coefficient of ultrafiltration and relative change of total density of pore liquid significantly affect the contaminant migration process. Compared with a single drainage boundary, the pore pressure dissipation and contaminant migration in a double drainage soil layer are much faster. The longer the loading time of mechanical loading, the more significant the negative pore pressure caused by the concentration gradient.

Behavior of uranium(VI) in the presence of a geomaterial: an aquifer sediment

Sediments from aquatic environments can be contaminated with uranium from natural and anthropogenic sources; the behavior of U(VI) was investigated in two natural (SPT and DS) and gamma-irradiated (SPT-I) aquifer sediments in batch systems. Sediments were characterized, and quartz, albite, and kaolinite were mainly found in both sediments by X-ray diffraction. The points of zero charge were 5.4, 5.3, and 5.5, and the organic matter percentages were 48.0, 46.0, and 4.7% for SPT, SPT-I, and DS, respectively. Uranyl nitrate solutions were put in contact with each sediment considering different parameters (pH, contact time, initial concentration of uranium, and temperature). DS sediment did not adsorb any quantity of uranium at different pH values; SPT and SPT-I, attained the highest q e values at pH 3.5–4. The results show chemisorption on homogenous materials and endothermic processes. Desorption behavior of U(VI)/SPT showed a hundred percent desorption with nitric acid and humic acid solutions; in the last case, it is due to the high stability constant of the complex of uranium with the humic acids. The results help to understand the contamination and decontamination processes of sediments with uranium, the bioavailability of uranium, the ecological risk of U-contaminated sediments, and remediation. Doses of 1 MGy of Co-60 gamma radiation did not affect the uranyl ions behavior in the aquifer sediment.

Chaotic Mixing Experiments: Unravelling Contamination Processes on Dacitic Melts

Magmas are the ultimate source of volcanism on Earth. At high-temperatures these complex silicate melts may easily chaotically mix, on their way towards the surface of the planet.The Paraná-Etendeka Magmatic Province (PEMP), one of the largest volcanic provinces of our planet, serves as the focus of this experimental study. The investigation simulates the contamination of high-Ti dacites passing through the continental crust. Our final aim is to contribute to the origin of the high-Ti Chapecó dacites from PEMP, with particular attention to the genesis of Chapecó-Ourinhos dacites (COD).The experimental apparatus is based on the Journal Bearing System. All experimental runs have been operated at atmospheric pressure and a temperature of 1500 °C. A dacitic magma chamber under the assimilation of crustal material has been simulated. The resulting experimental products (dry/bubble free glasses) exhibit concentric folded and stretched filaments of contrasting compositions. The calculated fractal dimension for a representative section is Dbox = 1.60(3), confirming the achievement of chaotic dynamics. Electron Microprobe Analysis (EMPA) from the experimental glasses clearly shows SiO2-contamination, while Al2O3-data indicate lower contamination levels. As a consequence, different elements depict dissimilar curves in chemical transects. We used the parameter σn2 (normalized variance) to quantify the mixing efficiency and differential elemental mobilities. In addition, our data reproduced the chemical behaviour of some elements in COD- dacites, especially the network formers such as Fe, Al, Ti and Si. EMPA reveals clear deviations from the linear mixing model. Our experiments and data replicate a selective contamination process. Differential elemental mobilities could be calculated. Comparisons with natural data depict how the mixing involving Chapecó-Guarapuava (CGD) and Chapecó-Ourinhos (COD) dacitic end-members may have contributed to the generation of more evolved COD from the interaction of CGD pre-existing melts with crustal rocks from the PEMP basement via chaotic dynamics.

Unveiling Pyrolysis Mechanisms of Waste Printed Circuit Boards Through Multiphysics Simulation

The pyrolysis process of waste printed circuit board (WPCB) with high economic benefit has been a black box problem, limiting the upgrading of pyrolysis processes. The resourcefulness and hazardous nature of WPCB will make it necessary for it to be treated properly. Multiphysics model was built to simulate the whole processes of WPCB pyrolysis and contaminants’ release. The circuit board samples containing six components were selected for pyrolysis in a tube furnace at a rate of 10[Formula: see text]C/min from room temperature to 600[Formula: see text]C, and the residual rate of Br- was determined by the oxygen bomb method. The results showed that the difference in temperature distribution could be attributed to thermal conductivity and surface area. Heat distribution would be more even from the inner material in areas where holes existed. The assembly method would affect the stress distribution around the components. Thermal stress at the pins might cause the separation of components from the substrate. The concentration of brominated contaminants was influenced by the material and assembly method. The instantaneous concentration around the pin was 3–4 times compared to the bare substrate, which was beneficial for the release and control of brominated organics. This study provided the research method for the in-depth understanding of the pyrolysis process of complex materials; and provided a basis for the upgrading of related processes.

Multiple contamination sources, pathways and conceptual model of complex buried karst water system:constrained by hydrogeochemistry and δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr isotopes

Karst groundwater contamination has emerged as a worldwide environmental and health hazard. Karst aquifers, even for the buried karst systems, have strong contamination sensitivity and great pollution risk due to the good pipe fracture connectivity. The large burial depth and invisible hydrologic connectivity pose a challenge for the diagnosis of the contamination sources and identification of the contamination pathways of buried karst aquifers. To address it, a comprehensive application of hydrogeological and hydrogeochemical investigation combined with multiple isotopes (δ2H, δ18O, δ34S, δ13C and 87Sr/86Sr) were performed to elucidate the multiple contamination sources and migration pathways of contaminants in Jinci Spring, a complex buried karst water system. The results obtained highlight that the hydrological connectivity and source availability determine the specific contamination process in buried karst aquifer. Karst aquifer under the river channel is observed to be influenced by the vertical infiltration of polluted river water as indicated by elevated chloride levels (mean 79.4 mg/L) and higher δ2H (mean −8.8 ‰) and δ18O (mean −64.5 ‰) values. Evidenced by the excess of sulfate (mean: 1454 mg/L) and depleted δ34S (mean: −1.6 ‰), the lower karst aquifer may receive the leaking recharge of the mining waste water in the overlying coal seams. The occurrence of nitrate in karst water may be induced by reverse recharge from neighboring confined quaternary aquifers, indicated by the elevated nitrate concentration (15.0–50.8 mg/L) with high 87Sr/86Sr ratios (mean 0.7124). Our findings suggest that over-pumping of deep karst waters may produce additional pollution sources by altering the natural recharge relationship between montanic karst waters and the neighboring pore waters within the basin. Research in this paper improves our understanding of groundwater pollution and hydrological connectivity in buried carbonate aquifers and the protection of karst water resources.

Assessment of soil-groundwater nitrogen cycling processes in the agricultural region through flux model, stable isotope

The nitrogen cycle in the soil-groundwater system of agricultural land is a crucial process within the global nitrogen cycle. Human activities have significantly intensified this cycling process in agricultural fields, consequently leading to substantial accumulation of nitrogen in the soil-groundwater system and giving rise to numerous ecological health issues. Quantitative assessment of soil-groundwater nitrogen cycling processes can facilitate the optimization of nitrogen management strategies in agricultural fields and the prevention and management of groundwater nitrogen pollution. However, accurately quantifying the intricate soil-groundwater nitrogen cycling dynamics in agro-irrigation areas characterized by diverse nitrogen sources and complex hydrogeological conditions poses a significant challenge. The Songhua River Basin in the Sanjiang Plain was selected as the study area for this investigation. We utilized the INCA-N model to simulate annual nitrogen fluxes in the soil-groundwater system of an agricultural watershed, and employed stable isotope and water chemistry methods to identify sources of groundwater nitrogen contamination and transformation processes. Ultimately, we conducted a comprehensive assessment of nitrogen cycling within the soil-groundwater system of the agricultural watershed. The findings revealed that atmospheric deposition, nitrogen fixation, and fertilization constituted the primary mechanisms of soil nitrogen input. Plant uptake, riverine nitrogen transport, and denitrification were identified as the three principal processes responsible for soil-groundwater nitrogen export. The results obtained from the MIXSIAR model demonstrate a substantial contribution of nitrogen fertiliser and soil nitrogen to groundwater nitrate, followed by faeces and sewage. Additionally, the annual input fluxes of nitrogen simulated by INCA-N reveal that fertiliser application is the primary contributor, which aligns to some extent with the findings of the MIXSIAR model. Soil nitrogen can serve as a relatively stable source of groundwater nitrate, while anthropogenic activities such as fertilizer application, manure deposition, and sewage discharge are likely to be the primary drivers of groundwater nitrate pollution. By quantifying the N input and output fluxes, it was determined that approximately 58% of the total annual nitrogen input has the potential to accumulate within the soil-groundwater system. The effective utilization of legacy nitrogen can contribute to the reduction of soil-groundwater nitrogen fluxes, while maintaining crop yields and mitigating greenhouse gas emissions. This study aims to optimize nitrogen management practices in agricultural areas and provide valuable insights for water conservation strategies.

Analysis of contaminant dispersion in constructed wetland flows with absorptive boundaries

Pollution in wetland flows poses a significant challenge to ecosystem preservation, underscoring the importance of wetland restoration. Constructed wetlands have emerged as a widely embraced solution for contaminant mitigation. In this study, we focus on the contaminant removal process within the wetland flows to contribute to wetland restoration. A constructed wetland with ecological floating and bottom absorptive beds has been employed to enhance the capacity of contaminant removal within wetland flows. However, the environmental dispersion in constructed wetland flows is further complicated by the presence of irreversible first-order absorptive boundaries at the upper and bottom beds. Therefore, our work focuses on comprehending the expansion processes of contaminant clouds under absorptive boundaries through a multiscale analysis to demonstrate the removal effects of constructed wetlands. The findings highlight significant deviations in the spatial distribution of contaminant clouds, particularly in the vertical dimension, attributed to absorptive effects. To analyze the impact of removal mechanisms on the dispersion patterns of contaminant clouds, variations in the vertical concentration peak are examined. A predictive model is developed to estimate the position of the concentration crest in the vertical direction based on changes in absorptive ratios between the upper and bottom boundaries. Furthermore, in order to explore the key factor on removal capacity and efficiency within constructed wetland flows, we look into the process of contaminant depletion by examining variations in removed mass and local absorptive and removal efficiency along the streamwise direction in response to deviations in absorptive strengths at the upper and bottom beds. The ratios of the two boundary removal intensities play a significant role in the absorptive dynamics within wetland flows, particularly during the early stages of cloud expansion. By adjusting the absorption ratio between two absorptive beds to 1:1 with a certain total depletion strength in wetland flows, the enhancement ratio of depletion efficiency can increase by nearly 30%. It has been proven that employing identical absorption strengths at two absorptive beds is an economical and efficient means to amplify the absorption efforts within designed constructed wetland flows. This study provides guidelines for the design of constructed wetlands aimed at enhancing their capacity for sewage treatment.

Application of Mesoporous Silicas for Adsorption of Organic and Inorganic Pollutants from Rainwater.

Precipitation is an important factor that influences the quality of surface water in many regions of the world. The pollution of stormwater runoff from roads and parking lots is an understudied area in water quality research. Therefore, a comprehensive analysis of the physicochemical properties of rainwater flowing from parking lots was carried out, considering heavy metals and organic micropollutants. High concentrations of zinc were observed in rainwater, in addition to alkanes, e.g., tetradecane, hexadecane, octadecane, 2,6,10-trimethyldodecane, 2-methyldodecane; phenolic derivatives, such as 2,6-dimethoxyphenol and 2,4-di-tertbutylphenol; and compounds such as benzothiazole. To remove the contaminants present in rainwater, adsorption using silica carriers of the MCF (Mesostructured Cellular Foams) type was performed. Three groups of modified carriers were prepared, i.e., (1) SH (thiol), (2) NH2 (amino), and (3) NH2/SH (amine and thiol functional groups). The research problem, which is addressed in the presented article, is concerned with the silica carrier influence of the functional group on the adsorption efficiency of micropollutants. The study included an evaluation of the effects of adsorption dose and time on the efficiency of the contaminant removal process, as well as an analysis of adsorption isotherms and reaction kinetics. The colour adsorption from rainwater was 94-95% for MCF-NH2 and MCF-NH2/SH. Zinc adsorbance was at a level of 90% for MCF-NH2, and for MCF-NH2/SH, 52%. Studies have shown the high efficacy (100%) of MCF-NH2 in removing organic micropollutants, especially phenolic compounds and benzothiazole. On the other hand, octadecane was the least susceptible to adsorption in each case. It was found that the highest efficiency of removal of organic micropollutants and zinc ions was obtained through the use of functionalized silica NH2.

Multiscale pore‐network reconstruction of a fine‐textured heterogeneous soil

AbstractDigital samples offer many opportunities to study subsurface fluid flow and contaminant transport processes. The pore size distribution of especially fine‐textured porous media often covers many orders of magnitude in the length scale, which makes accurate microCT scanning and modeling of the underlying processes difficult. When a single‐resolution image is not capable of capturing all relevant details of a sample, one should scan the sample, or selected parts of it, at different resolutions. Combining multiple resolutions into one single sample for subsequent pore‐scale modeling is generally not possible due to limitations in computer memory and speed, thus making it necessary to create a simpler sample containing relevant information from the parent networks. We imaged four samples using different resolutions to capture the multiscale heterogeneity of a fine‐textured soil and combined them into one overall digital sample based on the original pore networks. The parent networks were characterized using their geometrical properties, correlations between these properties, and connectivity functions describing the network topologies. Our approach creates stochastic networks of arbitrary size with the same flow properties as the parent network. The method, implemented using the PoreStudio pore network model, repeatedly integrates information at two subsequent scales, with the resulting digital sample having the same hydraulic properties as the original samples. The procedure leads to more useful three‐dimensional digital models, facilitating basic analyses of underlying pore size distributions. Porosity calculations were compared with direct measurements, while those for the hydraulic conductivity were compared with estimates based on the particle size distribution and nearby field data.

Pulsed Laser Ablation Characteristics of Light-Absorbing Mask Layer Based on Coating Thicknesses under Laser Lift-Off Patterning Process.

Thin transparent oxide layers are typically patterned for use in electronic products including semiconductors, displays, and solar cells for applications such as transparent electrodes, insulating films, and encapsulation films. Conventional patterning methods have traditionally been used in photolithography and lift-off processes. Photolithography employs the wet development process, which has disadvantages such as potential undercut effects, swelling, chemical contamination, and high process costs. On the other hand, laser ablation, which has the advantages of high accuracy, high speed, a noncontact nature, and selective processing, can be used to pattern thin films. However, absorption in transparent oxide films is usually low. In this study, experiments were conducted to determine the ablation characteristics of mask layers. The factors affecting ablation, including beam radii, fluences, overlap ratios, and coating thicknesses, were examined; and the parameters characteristic of residue-free ablation, namely the ablation threshold, minimum fluence, and minimum ablation linewidth, were also examined. The experimental results revealed that the beam radius was an important parameter in determining the resolutions of transparent films and substrates.

Contaminant Transport Modeling and Source Attribution With Attention‐Based Graph Neural Network

AbstractGroundwater contamination induced by anthropogenic activities has long been a global issue. Characterizing and modeling contaminant transport processes is crucial to groundwater protection and management. However, challenges still exist in process complexity, data constraint, and computational cost. In the era of big data, the growth of machine learning has led to new opportunities in studying contaminant transport in groundwater systems. In this work, we introduce a new attention‐based graph neural network (aGNN) for modeling contaminant transport with limited monitoring data and quantifying causal connections between contaminant sources (drivers) and their spreading (outcomes). In five synthetic case studies that involve varying monitoring networks in heterogeneous aquifers, aGNN is shown to outperform LSTM‐based (long‐short term memory) and CNN‐ based (convolutional neural network) methods in multistep predictions (i.e., transductive learning). It also demonstrates a high level of applicability in inferring observations for unmonitored sites (i.e., inductive learning). Furthermore, an explanatory analysis based on aGNN quantifies the influence of each contaminant source, which has been validated by a physics‐based model with consistent outcomes with an R2 value exceeding 92%. The major advantage of aGNN is that it not only has a high level of predictive power in multiple scenario evaluations but also substantially reduces computational cost. Overall, this study shows that aGNN is efficient and robust for highly nonlinear spatiotemporal learning in subsurface contaminant transport, and provides a promising tool for groundwater management involving contaminant source attribution.

Monitoring Photo-Fenton and Photo-Electro-Fenton process of contaminants emerging concern by a gas diffusion electrode using Ca10-xFex-yWy(PO4)6(OH)2 nanoparticles as heterogeneous catalyst

The catalytic performance of modified hydroxyapatite nanoparticles, Ca10-xFex-yWy(PO4)6(OH)2, was applied for the degradation of methylene blue (MB), fast green FCF (FG) and norfloxacin (NOR). XPS analysis pointed to the successful partial replacement of Ca by Fe. Under photo-electro-Fenton process, the catalyst Ca4FeII1·92W0·08FeIII4(PO4)6(OH)2 was combined with UVC radiation and electrogenerated H2O2 in a Printex L6 carbon-based gas diffusion electrode. The application of only 10 mA cm−2 resulted in 100% discoloration of MB and FG dyes in 50 min of treatment at pH 2.5, 7.0 and 9.0. The proposed treatment mechanism yielded maximum TOC removal of ∼80% and high mineralization current efficiency of ∼64%. Complete degradation of NOR was obtained in 40 min, and high mineralization of ∼86% was recorded after 240 min of treatment. Responses obtained from LC-ESI-MS/MS are in line with the theoretical Fukui indices and the ECOSAR data. The study enabled us to predict the main degradation route and the acute and chronic toxicity of the by-products formed during the contaminants degradation.

Behaviors of laser-induced damage of dye cell windows at low fluences and their mechanism analysis

In most liquid dye lasers, dye cell windows are the optical components most susceptible to laser damage even at very low fluences. Although various mechanisms and mitigation techniques have been explored, damage still occurs at some point, and some behaviors of the process cannot be effectively explained. In this work, we investigated three special behaviors of dye cell window damage which cannot be explained by ordinary laser-induced damage mechanisms. We proposed that damage to dye cell windows can be caused by a contamination process similar to laser-induced contamination (LIC) on space optics, and used the LIC mechanism to analyze the cause of those damage behaviors. Additional experiments and calculations were conducted, providing more evidence in support of the analysis. In addition, it was found that dye molecules, which are necessary for dye lasers, are the primary contaminants in the LIC process. This explains the inevitable damage to dye cell windows.

A review of the effects of typical biogeochemical and hydrogeological features on the natural attenuation of soil petroleum contaminants

Oil spills in soil can form source areas of contamination that are ecologically hazardous in the long term. The natural process by which the concentration, toxicity and mobility of petroleum contaminants in soil decrease under the combined effects of biochemistry and other aspects without human interference is called natural attenuation. This paper provides a systematic review of the natural attenuation characteristics of petroleum contaminants in soil and its research tools, focusing on the typical biogeochemical and hydrogeological characteristics of the site, and describes the influence of both on the natural attenuation process of contaminants in soil and its mechanism. It also clarifies the influence of petroleum properties, sediment types, organic matter changes, photo-oxidation reactions and microorganisms on the natural attenuation of the source area, and summarises the relevant indicators that can characterise the natural attenuation of petroleum contamination in the source area; at the same time, it outlines the various types of prediction methods of natural attenuation processes, and points out the focus and difficulties of the multidisciplinary fusion of the research directions and the multi-data drive, and finally puts forward a proposal for the study of natural attenuation of petroleum in soils. Finally, the research on the natural attenuation of soil oil pollution source area is proposed. Overall, due to the complexity of organic matter, mineral and microbial components, and the inhomogeneity of hydrogeological conditions, the study of the influence of the intrinsic properties of the site on the natural attenuation of pollutants needs to be further strengthened, and this paper focuses on the identification of the spatial and temporal dynamics of the natural attenuation of pollutants, and the deepening of the understanding of the interaction mechanisms between typical biogeochemical and hydrogeological conditions of the site and the pollutants.