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Research

13 pages, 2525 KiB

Open AccessArticle

Effects of L-Aspartic Acid on Cr(VI) Adsorption onto the Lepidocrocite with Different Exposed Facets: Batch Experiments and In Situ ATR-FTIR Analysis

by Xiaofei Li, Tianfu Li, Xiaohu Jin, Yanfu Wei, Yanping Bao, Qian Yao, Fuhua Li, Weicheng Xu and Xiaolian Wu

Processes 2024, 12(11), 2598; https://doi.org/10.3390/pr12112598 - 19 Nov 2024

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Abstract

The adsorption of toxic metals onto iron oxides is a prevalent geochemical process in natural environments. Organic acids are known to modify the adsorption features of toxic ions through either competitive or cooperative effects. Nowadays, the toxic metal adsorption influenced by organic acids [...] Read more.

The adsorption of toxic metals onto iron oxides is a prevalent geochemical process in natural environments. Organic acids are known to modify the adsorption features of toxic ions through either competitive or cooperative effects. Nowadays, the toxic metal adsorption influenced by organic acids on iron oxides with varying facet exposures is not fully understood. This study explored how L-Aspartic acid (LA) influences Cr(VI) adsorption on two different exposure facets of lepidocrocite through batch adsorption experiments, in situ ATR-FTIR spectroscopy, and 2D-COS analysis. The results reveal that LA competes for available binding sites on lepidocrocite, consequently inhibiting the adsorption of Cr(VI). Rod-shaped lepidocrocite (R-LEP) owns more (001) facets and shows stronger Cr(VI) adsorption and LA competition than plate-like lepidocrocite (P-LEP), which mainly has (010) facets. The data for Cr(VI) uptake on both P-LEP and R-LEP within the effect of LA are well-fitted by the pseudo-second-order kinetics and the Freundlich isotherm model, suggesting chemical interaction as the dominant process for Cr(VI) coordination on lepidocrocite. Cr(VI) ions favor interaction with R-LEP over P-LEP, forming inner-sphere complexes on (001) facets. Concurrently, LA’s carboxyl groups can compete for the active sites on the lepidocrocite surfaces, engaging in anion exchange with hydroxyl groups, and forming outer-sphere and inner-sphere structures. This competitive effect is particularly pronounced in the R-LEP system. The current findings are expected to broaden insights into how the exposed facets of lepidocrocite influence the fate of Cr(VI) in the organic acid coexistence environment. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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12 pages, 3336 KiB

Open AccessArticle

Preparation and Exploration of Spherical Fe-C Micro-Electrolysis Materials for the Removal of Crystal Violet

by Min Dai, Xixi Wei, Chihpeng Lin, Chunsheng Xie, Zimin Lai, Wencan Zhu, Junhao Guo and Changsheng Peng

Processes 2024, 12(11), 2538; https://doi.org/10.3390/pr12112538 - 14 Nov 2024

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Abstract

In this paper, the spherical Fe-C micro-electrolysis materials (Fe-C MEM) were prepared using iron powder, activated carbon powder, corn straw, and bentonite as the raw materials. The preparation conditions optimized by single factor test showed Fe-C MEM had a high crystal violet removal [...] Read more.

In this paper, the spherical Fe-C micro-electrolysis materials (Fe-C MEM) were prepared using iron powder, activated carbon powder, corn straw, and bentonite as the raw materials. The preparation conditions optimized by single factor test showed Fe-C MEM had a high crystal violet removal and strength under 1:1 of Fe/C ratio, 2% corn straw content, 25% bentonite content, and 900 °C sintering temperature. The porous Fe-C MEM had a high specific surface area of 108.069 m²/g with an even distribution of zero-valent iron and carbon. The maximum removal capacity of CV by Fe-C MEM was 105.48 mg/g at 25 °C. The CV removal was a spontaneous endothermic process. The mechanism of CV removal by Fe-C MEM was adsorption combined with degradation. Fe-C MEM has a good performance in dye wastewater treatment. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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20 pages, 5328 KiB

Open AccessArticle

Impact of Acid Rain on Release Characteristics of Heavy Metals in Low-Sulfur Tailings with Strong Acid Neutralization Capacity: A Case Study from Northern Guangxi, China

by Xiaohua Shu, Dinghua Zhang, Qian Zhang, Tao Ai, Xuehong Zhang and Jie Liu

Processes 2024, 12(11), 2492; https://doi.org/10.3390/pr12112492 - 9 Nov 2024

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Abstract

Tailing ponds are major sources of heavy metal pollution. Previous studies primarily focused on tailings with high sulfur content, with limited attention to low-sulfur tailings. This study explored the release behavior of Pb, Zn, and Cd from low-sulfur tailings under simulated acid rain [...] Read more.

Tailing ponds are major sources of heavy metal pollution. Previous studies primarily focused on tailings with high sulfur content, with limited attention to low-sulfur tailings. This study explored the release behavior of Pb, Zn, and Cd from low-sulfur tailings under simulated acid rain conditions, considering factors such as pH, particle size, and weathering degree. Samples were collected from a lead–zinc tailing pond in the karst regions of northern Guangxi, China. Batch leaching experiments indicated that even with high acid neutralization capacity (ANC = 166.57–167.45 kg H₂SO₄/t), substantial heavy metal leaching occurred under acidic conditions (pH 2–3), with Pb, Zn, and Cd concentrations increasing 4–6 times compared to neutral conditions. Leachate concentrations were slightly higher in coarser particles than in finer ones, while weathering further enhanced metal release, particularly for Cd. These findings suggest that acid neutralization alone may not be sufficient to prevent heavy metal leaching in low-sulfur tailings exposed to acid rain. However, due to the laboratory scale of this study, further validation through field-scale or mesocosm experiments is necessary to confirm the observed trends and assess their implications for environmental risk management in karst regions. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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10 pages, 1372 KiB

Open AccessArticle

The Effects of Water Management, Foliar Fertilizers, and Lime Application on the Accumulation of Cd and As in Rice Grains Based on a Field Trial

by Qiming Wang, Wanchuan Du, Xiaodan Jin, Jian Wang, Yannan Lu, Dating Huang, Jiaying Nong, He Huang, Tian Xie and Biao Han

Processes 2024, 12(10), 2241; https://doi.org/10.3390/pr12102241 - 14 Oct 2024

Viewed by 679

Abstract

The aim of this study was to explore the feasible measurement of the control of cadmium (Cd) and arsenic (As) accumulation in rice grains. A field experiment was carried out to research the effect of different treatments, including spraying silicon (Si)/selenium (Se) foliar [...] Read more.

The aim of this study was to explore the feasible measurement of the control of cadmium (Cd) and arsenic (As) accumulation in rice grains. A field experiment was carried out to research the effect of different treatments, including spraying silicon (Si)/selenium (Se) foliar fertilizers, the application of lime (CaO), water management (continuous flooding), and the co-application of foliar fertilizers and flooding, on Cd and As accumulation in rice grains in Guangxi Province. The results indicate that Cd accumulation in rice grains decreased under different treatments and Cd content in rice grains reached the threshold of 0.2 mg kg⁻¹. In the single technical treatments, CaO application, flooding, spraying foliar Se fertilizer, and spraying foliar Si fertilizer decreased Cd content by 73.15%, 60.44%, 45.76%, and 36.07%, respectively. However, flooding and CaO amendment enhanced As accumulation in rice grains. The co-application of flooding and spraying foliar fertilizer can simultaneously reduce Cd and As in rice grains. In addition, they resulted in lower Cd content than the single technical treatments. Among the treatments, the lowest bioaccumulation factors of Cd and As were found after the co-application of flooding and Si foliar fertilizer, which decreased these factors by 74.02% and 22.72%, respectively. These results suggest that spraying foliar Si fertilizer combined with flooding may be a promising method to synchronously inhibit the accumulation of Cd and As in rice. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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15 pages, 11022 KiB

Open AccessArticle

Nano-Hydroxyapatite Modified Tobacco Stalk-Based Biochar for Immobilizing Cd(II): Interfacial Adsorption Behavior and Mechanisms

by Tianfu Li, Xiaofei Li, Chaoran Shen, Dian Chen, Fuhua Li, Weicheng Xu, Xiaolian Wu and Yanping Bao

Processes 2024, 12(9), 1924; https://doi.org/10.3390/pr12091924 - 7 Sep 2024

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Abstract

Biochar, an eco-friendly, porous carbon-rich material, is widely studied for immobilizing heavy metals in contaminated environments. This study prepared tobacco stalks, a typical agricultural waste, into biochar (TSB) modified by hydroxyapatite (HAP) at co-pyrolysis temperatures of 350 °C and 550 °C to explore [...] Read more.

Biochar, an eco-friendly, porous carbon-rich material, is widely studied for immobilizing heavy metals in contaminated environments. This study prepared tobacco stalks, a typical agricultural waste, into biochar (TSB) modified by hydroxyapatite (HAP) at co-pyrolysis temperatures of 350 °C and 550 °C to explore its Cd(II) adsorption behavior and relevant mechanisms. XRD, SEM–EDS, FTIR, and BET analyses revealed that HAP successfully incorporated onto TSB, enriching the surface oxygen-containing functional groups (P–O and carboxyl), and contributing to the enhancement of the specific surface area from 2.52 (TSB350) and 3.63 m²/g (TSB550) to 14.07 (HAP–TSB350) and 18.36 m²/g (HAP–TSB550). The kinetics of Cd(II) adsorption onto TSB and HAP–TSB is well described by the pseudo-second-order model. Isotherm results revealed that the maximum adsorption capacities of Cd(II) on HAP–TSB350 and HAP–TSB550 were approximately 13.17 and 14.50 mg/g, 2.67 and 9.24 times those of TSB350 and TSB550, respectively. The Cd(II) adsorption amounts on TSBs and HAP–TSBs increased significantly with increasing pH, especially in HAP–TSB550. Ionic strength effects and XPS analysis showed that Cd(II) adsorption onto HAP–TSBs occurred mainly via electrostatic interaction, cation exchange with Ca²⁺, complexation with P–O and –COOH, and surface precipitation. These findings will provide a modification strategy for the reutilization of tobacco agricultural waste in the remediation of heavy metal contaminated areas. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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18 pages, 19107 KiB

Open AccessArticle

Screening and Optimization of Soil Remediation Strategies Assisted by Machine Learning

by Bowei Zhang, Xin Wang and Chongxuan Liu

Processes 2024, 12(6), 1157; https://doi.org/10.3390/pr12061157 - 3 Jun 2024

Cited by 1 | Viewed by 852

Abstract

A numerical approach assisted by machine learning was developed for screening and optimizing soil remediation strategies. The approach includes a reactive transport model for simulating the remediation cost and effect of applicable remediation technologies and their combinations for a target site. The simulated [...] Read more.

A numerical approach assisted by machine learning was developed for screening and optimizing soil remediation strategies. The approach includes a reactive transport model for simulating the remediation cost and effect of applicable remediation technologies and their combinations for a target site. The simulated results were used to establish a relationship between the cost and effect using a machine learning method. The relationship was then used by an optimization method to provide optimal remediation strategies under various constraints and requirements for the target site. The approach was evaluated for a site contaminated with both arsenic and polycyclic aromatic hydrocarbons at a former shipbuilding factory in Guangzhou City, China. An optimal strategy was obtained and successfully implemented at the site, which included the partial excavation of the contaminated soils and natural attenuation of the residual contaminated soils. The advantage of the approach is that it can fully consider the natural attenuation capacity in designing remediation strategies to reduce remediation costs and can provide cost-effective remediation strategies under variable constraints for policymakers. The approach is general and can be applied for screening and optimizing remediation strategies at other remediation sites. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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16 pages, 23191 KiB

Open AccessArticle

Assessing Phytoremediation Potential: Dominant Plants in Soils Impacted by Polymetal(loid)lic Mining

by Boxin Wang, Juan Hou, Xueyong Wu, Xuekui Niu and Fengping Zhou

Processes 2024, 12(4), 833; https://doi.org/10.3390/pr12040833 - 19 Apr 2024

Viewed by 1120

Abstract

Phytoremediation, an ecological approach aimed at addressing polymetal(loid)lic-contaminated mining soils, has encountered adaptability challenges. Dominant plant species, well-suited to the local conditions, have emerged as promising candidates for this purpose. This study focused on assessing the phytoremediation potential of ten plant species that [...] Read more.

Phytoremediation, an ecological approach aimed at addressing polymetal(loid)lic-contaminated mining soils, has encountered adaptability challenges. Dominant plant species, well-suited to the local conditions, have emerged as promising candidates for this purpose. This study focused on assessing the phytoremediation potential of ten plant species that thrived in heavy metal(loid)-contaminated mining soils. This investigation covered nine heavy metal(loid)s (As, Cu, Cd, Cr, Hg, Ni, Pb, Sn, and Zn) in both plants and rhizosphere soils. The results revealed a significant impact of mining activities, with heavy metal(loid) concentrations surpassing the Yunnan Province’s background levels by 1.06 to 362 times, highlighting a significant concern for remediation. The average levels of the heavy metal(loid)s followed the order of As (3.98 × 10³ mg kg⁻¹) > Cu (2.83 × 10³ mg kg⁻¹) > Zn (815 mg kg⁻¹) > Sn (176 mg kg⁻¹) > Pb (169 mg kg⁻¹) > Cr (68.1 mg kg⁻¹) > Ni (36.2 mg kg⁻¹) > Cd (0.120 mg kg⁻¹) > Hg (0.0390 mg kg⁻¹). The bioconcentration factors (BCFs), bioaccumulation factors (BAFs), and translocation factors (TFs) varied among the native plants, indicating diverse adaptation strategies. Low BCFs and BAFs (ranging from 0.0183 to 0.418 and 0.0114 to 0.556, respectively) suggested a low bioavailability of heavy metal(loid)s. Among the species, both J. effusus and P. capitata showed remarkable abilities for As accumulation, while A. adenophora demonstrated a notable accumulation ability for various heavy metal(loid)s, especially Cd, with relatively high BCFs (1.88) and BAFs (3.11), and the TF at 1.66 further underscored the crucial role of translocation in preventing root toxicity. These findings emphasized the potential of these plant species in mine ecological restoration and phytoremediation, guiding targeted environmental rehabilitation strategies. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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16 pages, 2018 KiB

Open AccessArticle

Adsorption of Zinc(II) Ion by Spent and Raw Agaricus bisporus in Aqueous Solution

by Xiaoyu Zhang, Caiyi Zhao, Feng Xue, Beicheng Xia, Yuanyuan Lu, Rongrong Ying and Zhewei Hu

Processes 2024, 12(4), 717; https://doi.org/10.3390/pr12040717 - 1 Apr 2024

Viewed by 1103

Abstract

A significant environmental concern globally is the pollution of water bodies as a result of heavy metals. To date, various attempts have been made to effectively remove heavy metals, such as those that use synthetic and biogenic materials to abate and control water [...] Read more.

A significant environmental concern globally is the pollution of water bodies as a result of heavy metals. To date, various attempts have been made to effectively remove heavy metals, such as those that use synthetic and biogenic materials to abate and control water pollution. The biological removal of pollutants from water is an efficient and environmentally friendly technique. In this study, we evaluated the biosorption characteristics of Zn²⁺ ions from aqueous solution by spent composed of raw Agaricus biosporium (RAB) and A. biosporium (SCAB). We added different biosorption doses, metal ions, and initial concentrations of pollutants to explore the adsorption of Zn²⁺ by RAB and SCAB. We applied pseudo-first- and second-order models to investigate the biosorption kinetics. According to our results, the rate of Zn²⁺ removal from the aqueous solution using raw biomass was significantly lower than that using sodium citrate-treated biomass of SCAB. When the Zn²⁺ concentration increased from 10 mg L⁻¹ to 200 mg L⁻¹, the rate of removal of RAB decreased from 73.9% to 38.4%, and that of Zn²⁺ by SCAB decreased from 99.9% to 75.9%. As we increased the biosorbent dose, the rate of Zn²⁺ removal by SCAB increased. Interestingly, Zn² biosorption was inhibited by heavy co ions (Cu²⁺ and Pb²⁺) and light metals (e.g., Na⁺, Mg²⁺, K⁺, and Ca²⁺). When treating wastewater polluted with Zn²⁺, Pb²⁺, and Cu²⁺, SCAB showed good potential. The results of this study provide a scientific basis for an environmentally sound approach to controlling water pollution. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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20 pages, 6483 KiB

Open AccessArticle

Comparing the Aging Processes of PLA and PE: The Impact of UV Irradiation and Water

by Xucheng Wang, Jinxin Chen, Wenhao Jia, Kaibo Huang and Yini Ma

Processes 2024, 12(4), 635; https://doi.org/10.3390/pr12040635 - 22 Mar 2024

Cited by 1 | Viewed by 2215

Abstract

The aging processes of microplastics (MPs) are prevalent in natural environments. Understanding the aging mechanisms of MPs is crucial for assessing their environmental behavior and potential risks. In this study, we selected polylactic acid (PLA) and polyethylene (PE) as representatives of biodegradable and [...] Read more.

The aging processes of microplastics (MPs) are prevalent in natural environments. Understanding the aging mechanisms of MPs is crucial for assessing their environmental behavior and potential risks. In this study, we selected polylactic acid (PLA) and polyethylene (PE) as representatives of biodegradable and conventional plastics, respectively, to examine changes in their physicochemical properties induced by water and UV light exposure. Laboratory aging resulted in significant fragmentation, characterized by cracks and pores on the surfaces, for both types of MPs, with PLA MPs exhibiting more severe changes, particularly under combined UV and water exposure. Notably, PLA MPs tended to become progressively smaller after aging, whereas PE MPs did not show significant size changes. Chemical analyses of aged MPs using micro-Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed a substantial increase in the carbonyl index (CI) and oxygen content for PE, suggesting surface oxidation during photo-oxidation. Conversely, PLA MPs displayed a CI decrease, along with an oxygen content increase, indicating the breakdown of ester linkages in PLA and the formation of other oxidation products. Furthermore, we developed and optimized pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) methods to identify potential chemical degradation products of PE and PLA, considering their differing thermal stabilities. We observed a distinct trend regarding the peaks in the chromatogram of aged MPs and identified the typical oxidation and crosslinking products for PLA. Additionally, after the aging process, both PE and PLA exhibited a significant increase in organic carbon content, with the eluate containing submicron/nano-sized particles. This study provides a scientific foundation for a deeper understanding of the environmental aging mechanisms of various MPs, particularly in regards to the effects of UV irradiation and water exposure. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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14 pages, 2135 KiB

Open AccessEditor’s ChoiceArticle

Utilizing Machine Learning Models with Molecular Fingerprints and Chemical Structures to Predict the Sulfate Radical Rate Constants of Water Contaminants

by Ting Tang, Dehao Song, Jinfan Chen, Zhenguo Chen, Yufan Du, Zhi Dang and Guining Lu

Processes 2024, 12(2), 384; https://doi.org/10.3390/pr12020384 - 14 Feb 2024

Viewed by 1825

Abstract

Sulfate radicals are increasingly recognized for their potent oxidative capabilities, making them highly effective in degrading persistent organic pollutants (POPs) in aqueous environments. These radicals excel in breaking down complex organic molecules that are resistant to traditional treatment methods, addressing the challenges posed [...] Read more.

Sulfate radicals are increasingly recognized for their potent oxidative capabilities, making them highly effective in degrading persistent organic pollutants (POPs) in aqueous environments. These radicals excel in breaking down complex organic molecules that are resistant to traditional treatment methods, addressing the challenges posed by POPs known for their persistence, bioaccumulation, and potential health impacts. The complexity of predicting interactions between sulfate radicals and diverse organic contaminants is a notable challenge in advancing water treatment technologies. This study bridges this gap by employing a range of machine learning (ML) models, including random forest (DF), decision tree (DT), support vector machine (SVM), XGBoost (XGB), gradient boosting (GB), and Bayesian ridge regression (BR) models. Predicting performances were evaluated using R², RMSE, and MAE, with the residual plots presented. Performances varied in their ability to manage complex relationships and large datasets. The SVM model demonstrated the best predictive performance when utilizing the Morgan fingerprint as descriptors, achieving the highest R² and the lowest MAE value in the test set. The GB model displayed optimal performance when chemical descriptors were utilized as features. Boosting models generally exhibited superior performances when compared to single models. The most important ten features were presented via SHAP analysis. By analyzing the performance of these models, this research not only enhances our understanding of chemical reactions involving sulfate radicals, but also showcases the potential of machine learning in environmental chemistry, combining the strengths of ML with chemical kinetics in order to address the challenges of water treatment and contaminant analysis. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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17 pages, 5508 KiB

Open AccessArticle

Quantitative Analysis of Soil Cd Content Based on the Fusion of Vis-NIR and XRF Spectral Data in the Impacted Area of a Metallurgical Slag Site in Gejiu, Yunnan

by Zhenlong Zhang, Zhe Wang, Ying Luo, Jiaqian Zhang, Xiyang Feng, Qiuping Zeng, Duan Tian, Chao Li, Yongde Zhang, Yuping Wang, Shu Chen and Li Chen

Processes 2023, 11(9), 2714; https://doi.org/10.3390/pr11092714 - 11 Sep 2023

Viewed by 1105

Abstract

Vis-NIR and XRF spectroscopy are widely used in monitoring heavy metals in soil due to their advantages of being fast, non-destructive, cost-effective, and non-polluting. However, when used individually, XRF and vis-NIR may not meet the accuracy requirements for Cd determination. In this study, [...] Read more.

Vis-NIR and XRF spectroscopy are widely used in monitoring heavy metals in soil due to their advantages of being fast, non-destructive, cost-effective, and non-polluting. However, when used individually, XRF and vis-NIR may not meet the accuracy requirements for Cd determination. In this study, we focused on the impact area of a non-ferrous metal smelting slag site in Gejiu City, Yunnan Province, fused the pre-selected vis-NIR and XRF spectra using the Pearson correlation coefficient (PCC), and identified the characteristic spectra using the competitive adaptive reweighted sampling (CARS) method. Based on this, a quantitative model for soil Cd concentration was established using partial least squares regression (PLSR). The results showed that among the four fusion spectral quantitative models constructed, the model combining vis-NIR spectral second-order derivative transformation and XRF spectral first-order derivative transformation (D2(vis-NIR) + D1(XRF)) had the highest coefficient of determination (R² = 0.9505) and the smallest root mean square error (RMSE = 0.1174). Compared to the estimation models built using vis-NIR and XRF spectra alone, the average computational time of the fusion models was reduced by 68.19% and 63.92%, respectively. This study provides important technical means for real-time and large-scale on-site rapid estimation of Cd content using multi-source spectral fusion. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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16 pages, 3671 KiB

Open AccessArticle

Effects of Lead Pollution on Photosynthetic Characteristics and Chlorophyll Fluorescence Parameters of Different Populations of Miscanthus floridulus

by Jianqiao Qin, Xueding Jiang, Jianhua Qin, Huarong Zhao, Min Dai, Hao Liu and Xi Chen

Processes 2023, 11(5), 1562; https://doi.org/10.3390/pr11051562 - 19 May 2023

Cited by 6 | Viewed by 1893

Abstract

This study was conducted in order to study the effect of different concentrations of lead pollution on the photosynthetic characteristics and growth of Miscanthus floridulus, and to reveal its photosynthetic adaptability to lead stress. The differences of gas exchange parameters, chlorophyll fluorescence [...] Read more.

This study was conducted in order to study the effect of different concentrations of lead pollution on the photosynthetic characteristics and growth of Miscanthus floridulus, and to reveal its photosynthetic adaptability to lead stress. The differences of gas exchange parameters, chlorophyll fluorescence characteristics and photosynthetic pigment of two Miscanthus floridulus populations, one population from Boluo an uncontaminated site, and another population from Dabaoshan, a mine site, were compared and studied through nutrient solution culture experiments treated with heavy metal lead (Pb) in green house. The results showed that (1) under Pb stress, the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), intercellular carbon dioxide concentration (Ci), and chlorophyll content (Chl) of the leaves of the two populations decreased in different amplitude. Under moderate and severe Pb stress (80 mg·L⁻¹, 120 mg·L⁻¹, 240 mg·L⁻¹), the plant biomass of non-mining population and mining population plants were 54.5%, 39.7%, 29.4% and 70.4%, 54.7%, 50.9% of the control, respectively. (2) Stomatal restriction was the main factor for the Pn’s decrease in the leaves of the non-mine population under light Pb stress, while the non-stomatal restriction was the main factor for Pn’s decrease in the leaves of the non-mine population under middle and high Pb stresses. (3) Under Pb stress, the maximum photochemical efficiency (Fv/Fm) and potential activity (Fv/Fo) of PS II reaction centers in the two populations of M. floridulus decreased. However, Fv/Fm and Fv/Fo showed a smaller decrease, but the capability to utilize light and the potential to activate PSII of the mine population remained higher than that of the non-mine population. The changes of photochemical quenching coefficient (qP) and non-photochemical quenching coefficient (NPQ) of PSⅡ showed that qP value decreased and NPQ value increased in the two populations under Pb stress. On the whole, the resistance mining area population had a low qP reduction and a large increase in NPQ. Electronic transfer rate (ETR) and PSII actual fluorescence efficiency (ΦPSII) of the mine population changed slightly under Pb stress. These results indicated that when under Pb stress, the electron transport activity and photosynthetic apparatus were damaged less in the mine population with high resistance than in the non-mine population with low resistance. Conclusion: the mining population of M. floridulus has strong tolerance to Pb, which is suitable for the pioneer species of gramineae in vegetation restoration construction in metal mining area. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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12 pages, 2693 KiB

Open AccessArticle

Performance and Bacteria Communities of a Full-Scale Constructed Wetland Treating the Secondary Effluent after Multi-Years’ Operation

by Siyuan Song, Baogui Wang, Tangwu Yang, Yumei Gu, Sheng Sheng, Dehua Zhao, Shuqing An and Aimin Li

Processes 2023, 11(5), 1469; https://doi.org/10.3390/pr11051469 - 12 May 2023

Cited by 2 | Viewed by 1271

Abstract

Constructed wetlands (CWs) had been widely used to treat the tailwater from sewage treatment plants. However, the enduring effectiveness of CWs was still unclear. Therefore, this study aimed to investigate the chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and total [...] Read more.

Constructed wetlands (CWs) had been widely used to treat the tailwater from sewage treatment plants. However, the enduring effectiveness of CWs was still unclear. Therefore, this study aimed to investigate the chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and total phosphorus (TP) removal efficiencies (RE) of the Hongze CW (HZ-CW) after multi-years’ operation. The average COD RE were 7.6% and 15.14% in the 4th and 5th year, respectively. The NH₄⁺-N RE was 78.33% and 46.04% in the 4th and 5th year, respectively, while the TP RE remained high at 66.86% and 64.68%. The high-throughput sequencing analysis revealed that the bacterial community of HZ-CW at the end of the 5th year exhibited a substantial abundance and diversity, and Proteobacteria and Bacteroidota were the dominant phyla with a relative abundance of 33.75–71.8% and 11.28–24.53% in different zones of HZ-CW. Ammonia oxidizing organisms (AOMs) presented much higher relative abundance (0.43–0.79%) in aerated pond (AP) and four free water surface flow CWs (FWS1–FWS4) than those of anammox bacteria, indicating the dominant role of nitrification in NH₄⁺-N removal. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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11 pages, 2145 KiB

Open AccessArticle

Analysis of Hydrochemical Characteristics and Causes of Drinking Water Sources in South China: A Case Study in Zhanjiang City

by Hang Wei, Qi Zou, Zhiliang Chen, Yingjie Cao, Shuang Wang, Fen Zhu and Xulong Liu

Processes 2023, 11(4), 1196; https://doi.org/10.3390/pr11041196 - 13 Apr 2023

Cited by 4 | Viewed by 1331

Abstract

The evaluation of groundwater environmental quality and the identification of recharge sources are very important for groundwater utilization. In this study, hydrochemistry and isotope analysis methods are used to investigate the recharge sources and hydrochemical processes of groundwater in Zhanjiang City. The results [...] Read more.

The evaluation of groundwater environmental quality and the identification of recharge sources are very important for groundwater utilization. In this study, hydrochemistry and isotope analysis methods are used to investigate the recharge sources and hydrochemical processes of groundwater in Zhanjiang City. The results show that all samples of groundwater were drawn on the left of the global meteoric water line (GMWL: δD = 8δ¹⁸O + 10) and local meteorological water lines (LMWL1: δD = 8.17δ¹⁸O + 11.74 and LMWL2: δD = 7.50δ¹⁸O + 6.18), indicating that the groundwater was mainly recharged by meteoric precipitation and influenced by the effect of evaporation. In the middle and deep confined aquifers, the isotope data depleted with the depth, indicating that there is a relatively weak hydraulic connection between them. In addition, compared with unconfined groundwater, the isotope data of confined groundwater showed relative depletion, indicating that the confined aquifer may be partially recharged from other confined aquifers. The main chemical types in the groundwater were Na*Ca-HCO₃. There are three major natural hydrochemical processes controlling the source of groundwater ions: silicate weathering, carbonate dissolution, and the cation exchange reaction. In addition, the differences in physical and chemical properties between unconfined groundwater and confined groundwater are significant. Due to the differences in anthropogenic activities and land-use types, the nitrate of the unconfined groundwater exceeds the groundwater standards. Due to the geological background of Zhanjiang City, iron and manganese exceed the third standard of groundwater in confined groundwater. Due to groundwater exploitation, TDS levels in confined groundwater have been increasing. Closed groundwater extraction is not sustainable, and it is depleting ancient water reserves. This study highlights the effectiveness of hydrochemistry and isotope analysis methods for identifying the recharge area and recharge mode of groundwater, andit is significant for fully understanding groundwater hydrochemistry and scientifically managing and protecting groundwater. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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15 pages, 4579 KiB

Open AccessArticle

Analysis of Natural Groundwater Flowing into the Flow Field of In Situ Leaching Mining

by Qinci Li, Zhaokun Li, Tingting Xie, Ye Ding, Nan Gan, Yahui Tan and Chong Zhang

Processes 2023, 11(2), 471; https://doi.org/10.3390/pr11020471 - 3 Feb 2023

Cited by 1 | Viewed by 4130

Abstract

This paper aims to quantitatively analyze the influence of natural groundwater flowing into the flow field of in situ leaching mining. The computational method was built to evaluate the effect of natural groundwater on the production efficiency of pumping wells for the in [...] Read more.

This paper aims to quantitatively analyze the influence of natural groundwater flowing into the flow field of in situ leaching mining. The computational method was built to evaluate the effect of natural groundwater on the production efficiency of pumping wells for the in situ leaching of uranium, and the “flow ratio of groundwater” and related formulas were defined. C1 and C2 mining areas of an in situ leaching uranium mine in Inner Mongolia were taken as an example, and the effect on the “flow ratio of groundwater” when changing the flow quantity of injection wells and the position and length of the filter in the pumping and injection wells were compared. The results show that the variation in the “flow ratio of groundwater” of a whole mining area or a single pumping well in different production stages can be obtained by the neutral solution concentration value from the mining area’s numerical simulation. Regulating the position, length of the filter, and mode of fluid injection in an in situ leaching mine can control the quantity of natural groundwater flowing into the mining area and reduce the fluid exchange between the flow field of in situ leaching uranium mining and natural groundwater. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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16 pages, 2727 KiB

Open AccessArticle

Differences in Physiological Metabolism and Antioxidant System of Different Ecotypes of Miscanthus floridulus under Cu Stress

by Jianqiao Qin, Zhiqiang Yan, Xueding Jiang, Huarong Zhao, Shasha Liu, Min Dai, Dexin Xiong and Xi Chen

Processes 2022, 10(12), 2712; https://doi.org/10.3390/pr10122712 - 15 Dec 2022

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Abstract

To reveal the similarities and differences in the resistance mechanisms of different ecotypes to Cu stress, a pot experiment was used to systematically compare the physiological responses of non-mining ecotype Miscanthus floridulus (collected from Boluo County, Huizhou City) and mining ecotype Miscanthus floridulus [...] Read more.

To reveal the similarities and differences in the resistance mechanisms of different ecotypes to Cu stress, a pot experiment was used to systematically compare the physiological responses of non-mining ecotype Miscanthus floridulus (collected from Boluo County, Huizhou City) and mining ecotype Miscanthus floridulus (collected from Dabaoshan mining area) under different Cu concentrations. The results showed that chlorophyll a, chlorophyll b and total chlorophyll in the leaves of the two ecotypes of M. floridulus were negatively correlated with Cu stress concentration (p < 0.01), but the extent of decrease for the ecotypes in the mining area was lower than that for the ecotypes in the non-mining area. The values of chlorophyll a/b for both ecotypes increased with increasing Cu treatment concentration, indicating that Cu is more harmful to chlorophyll b than to chlorophyll a for M. floridulus. Cu stress can lead to the accumulation of malondialdehyde (MDA) in the leaves of M. floridulus with the amount of MDA accumulation observed being greater in the non-mining ecotype than in the mining ecotype (p < 0.05). The content of antioxidant substances (ascorbic acid and reduced glutathione) in the mining ecotype M. floridulus was significantly higher than that in the non-mining ecotype. The activity of SOD in the leaves of non-mining ecotypes was inhibited by Cu stress and the activity of POD was increased by Cu stress. However, the increase in POD in the mining ecotypes was greater than that in the non-mining ecotypes and the activities of the two enzymes in the mining ecotypes were significantly higher than those in the non-mining ecotypes at the highest concentration of Cu. Cu had different effects on PPO activity in the leaves of the two ecotypes of M. floridulus. The plant leaves of the non-mining ecotype at 400 and 800 mg·kg⁻¹ were significantly fewer than those of the control group (p < 0.05), which were 87.1% and 65.2% of the control group, respectively. The PPO activity in the plant leaves of the mining ecotype was higher than that in the leaves of the non-mining ecotype and was significantly higher at 400 and 800 mg·kg⁻¹ than that of the control group (p < 0.05), at 226.5% and 268.1% of the control group, respectively. These results indicate that the mining ecotype M. floridulus is more resistant to copper stress, that resistant ecotypes have been formed, and that small-molecule antioxidant substances play an important role in increasing resistance levels. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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16 pages, 3166 KiB

Open AccessArticle

A Computational Framework for Design and Optimization of Risk-Based Soil and Groundwater Remediation Strategies

by Xin Wang, Rong Li, Yong Tian, Bowei Zhang, Ying Zhao, Tingting Zhang and Chongxuan Liu

Processes 2022, 10(12), 2572; https://doi.org/10.3390/pr10122572 - 2 Dec 2022

Cited by 5 | Viewed by 7323

Abstract

Soil and groundwater systems have natural attenuation potential to degrade or detoxify contaminants due to biogeochemical processes. However, such potential is rarely incorporated into active remediation strategies, leading to over-remediation at many remediation sites. Here, we propose a framework for designing and searching [...] Read more.

Soil and groundwater systems have natural attenuation potential to degrade or detoxify contaminants due to biogeochemical processes. However, such potential is rarely incorporated into active remediation strategies, leading to over-remediation at many remediation sites. Here, we propose a framework for designing and searching optimal remediation strategies that fully consider the combined effects of active remediation strategies and natural attenuation potentials. The framework integrates machine-learning and process-based models for expediting the optimization process with its applicability demonstrated at a field site contaminated with arsenic (As). The process-based model was employed in the framework to simulate the evolution of As concentrations by integrating geochemical and biogeochemical processes in soil and groundwater systems under various scenarios of remedial activities. The simulation results of As concentration evolution, remedial activities, and associated remediation costs were used to train a machine learning model, random forest regression, with a goal to establish a relationship between the remediation inputs, outcomes, and associated cost. The relationship was then used to search for optimal (low cost) remedial strategies that meet remediation constraints. The strategy was successfully applied at the field site, and the framework provides an effective way to search for optimal remediation strategies at other remediation sites. Full article

(This article belongs to the Special Issue Advances in Remediation of Contaminated Sites: Volume II)

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