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Qiu H, Xu J, Yuan Y, Alesi EJ, Liang X, Cao B. Low-disturbance land remediation using vertical groundwater circulation well technology: The first commercial deployment in an operational chemical plant. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 944:173804. [PMID: 38848922 DOI: 10.1016/j.scitotenv.2024.173804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2024] [Revised: 05/16/2024] [Accepted: 06/04/2024] [Indexed: 06/09/2024]
Abstract
Soil and groundwater contamination by organic pollutants from chemical plants presents significant risks to both environmental and human health. We report a significant field trial where a chemical plant in operation showed soil and groundwater pollution, as verified by sampling and laboratory tests. While many remediation methods are effective, they often require the temporary shutdown of plant operations to install necessary equipment. This paper introduces a novel combination of low-disturbance contaminant remediation technologies, including groundwater circulation well (GCW), pump and treat (P&T), and in-situ chemical oxidation (ISCO) technologies, that can be applied on the premises of an active plant without halting production. The groundwater with dissolved contaminants is removed through P&T and GCW, while GCW enhances ISCO that focus on eliminating the remaining hard-to-pump contaminants. Results show: (1) after two years of remediation effort, the contaminant levels in soil and groundwater were significantly reduced; (2) the average concentration reduction rate of four contaminants, including 1,2-dichloroethane, methylbenzene, ethylbenzene, and M&P-xylene, exceeds 98 %; (3) the presented remediation strategy results in the improvement of remediation efficiency. Specifically, the concentration of 1,2-dichloroethane in observation wells dropped from 40,550.7 μg/L to 44.6 μg/L. This study offers a first-of-its-kind commercial deployment of a GCW-based remediation strategy in an active plant setting. Moreover, the combined remediation approach presented here can serve as a model for designing contaminant remediation projects that require minimal operational disruption.
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Affiliation(s)
- Huiyang Qiu
- State Environmental Protection Key Laboratory of Soil Environmental Management and Pollution Control, Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China, Nanjing, Jiangsu, China; Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Jian Xu
- State Environmental Protection Key Laboratory of Soil Environmental Management and Pollution Control, Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China, Nanjing, Jiangsu, China.
| | - Yizhi Yuan
- Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada
| | - Eduard J Alesi
- IEG Technologie GmbH, Hohlbachweg 2, D-73344 Gruibingen, Baden-Württemberg, Germany
| | - Xin Liang
- Jiangsu Zhongchuan Ecological Environment Co., Ltd, China
| | - Benyi Cao
- School of Sustainability, Civil and Environmental Engineering, University of Surrey, Guildford, Surrey GU2 7XH, UK
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2
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Xu H, Zhang H, Qin C, Li X, Xu D, Zhao Y. Groundwater Cr(VI) contamination and remediation: A review from 1999 to 2022. CHEMOSPHERE 2024; 360:142395. [PMID: 38797207 DOI: 10.1016/j.chemosphere.2024.142395] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2023] [Revised: 05/13/2024] [Accepted: 05/20/2024] [Indexed: 05/29/2024]
Abstract
Hexavalent chromium (Cr(VI)) contamination of groundwater has traditionally been an environmental issue of great concern due to its bioaccumulative and highly toxic nature. This paper presents a review and bibliometric analysis of the literature on the interest area "Cr(VI) in groundwater" published in the Web of Science Core Collection from 1999 to 2022. First, information on 203 actual Cr(VI)-contaminated groundwater sites around the world was summarized, and the basic characteristics of the sources and concentrations of contamination were derived. 68.95% of the sites were due to human causes and 56.43% of these sites had Cr(VI) concentrations in the range of 0-10 mg/L. At groundwater sites with high Cr(VI) contamination due to natural causes, 75.00% of the sites had Cr(VI) concentrations less than 0.2 mg/L. A total of 936 papers on "Cr(VI) in groundwater" were retrieved for bibliometric analysis: interest in research on Cr(VI) in groundwater has grown rapidly in recent years; 59.4% of the papers were published in the field of environmental sciences. A systematic review of the progress of studies on the Cr(VI) removal/remediation based on reduction, adsorption and biological processes is presented. Out of 666 papers on Cr(VI) removal/remediation, 512, 274, and 75 papers dealt with the topics of reduction, adsorption, and bioremediation, respectively. In addition, several studies have demonstrated the potential applicability of natural attenuation in the remediation of Cr(VI)-contaminated groundwater. This paper will help researchers to understand and investigate methodological strategies to remove Cr(VI) from groundwater in a more targeted and effective manner.
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Affiliation(s)
- Huichao Xu
- Key Laboratory of Groundwater Resources and Environment of Ministry of Education, College of New Energy and Environment, Jilin University, Changchun, 130021, China; National and Local Joint Engineering Laboratory for Petrochemical Contaminated Site Control and Remediation Technology, Jilin University, Changchun, 130021, China; Jilin Provincial Key Laboratory of Water Resources and Environment, College of New Energy and Environment, Jilin University, Changchun, 130021, China
| | - Hui Zhang
- Key Laboratory of Groundwater Resources and Environment of Ministry of Education, College of New Energy and Environment, Jilin University, Changchun, 130021, China; National and Local Joint Engineering Laboratory for Petrochemical Contaminated Site Control and Remediation Technology, Jilin University, Changchun, 130021, China; Jilin Provincial Key Laboratory of Water Resources and Environment, College of New Energy and Environment, Jilin University, Changchun, 130021, China
| | - Chuanyu Qin
- Key Laboratory of Groundwater Resources and Environment of Ministry of Education, College of New Energy and Environment, Jilin University, Changchun, 130021, China; National and Local Joint Engineering Laboratory for Petrochemical Contaminated Site Control and Remediation Technology, Jilin University, Changchun, 130021, China; Jilin Provincial Key Laboratory of Water Resources and Environment, College of New Energy and Environment, Jilin University, Changchun, 130021, China
| | - Xiaoyu Li
- Key Laboratory of Groundwater Resources and Environment of Ministry of Education, College of New Energy and Environment, Jilin University, Changchun, 130021, China; National and Local Joint Engineering Laboratory for Petrochemical Contaminated Site Control and Remediation Technology, Jilin University, Changchun, 130021, China; Jilin Provincial Key Laboratory of Water Resources and Environment, College of New Energy and Environment, Jilin University, Changchun, 130021, China
| | - Dan Xu
- Key Laboratory of Groundwater Resources and Environment of Ministry of Education, College of New Energy and Environment, Jilin University, Changchun, 130021, China; National and Local Joint Engineering Laboratory for Petrochemical Contaminated Site Control and Remediation Technology, Jilin University, Changchun, 130021, China; Jilin Provincial Key Laboratory of Water Resources and Environment, College of New Energy and Environment, Jilin University, Changchun, 130021, China
| | - Yongsheng Zhao
- Key Laboratory of Groundwater Resources and Environment of Ministry of Education, College of New Energy and Environment, Jilin University, Changchun, 130021, China; National and Local Joint Engineering Laboratory for Petrochemical Contaminated Site Control and Remediation Technology, Jilin University, Changchun, 130021, China; Jilin Provincial Key Laboratory of Water Resources and Environment, College of New Energy and Environment, Jilin University, Changchun, 130021, China.
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3
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Gao M, Li X, Zhang Q, Li S, Wu S, Wang Y, Sun H. Spatial distribution of volatile organic compounds in contaminated soil and distinct microbial effect driven by aerobic and anaerobic conditions. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 927:172256. [PMID: 38583613 DOI: 10.1016/j.scitotenv.2024.172256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 04/01/2024] [Accepted: 04/04/2024] [Indexed: 04/09/2024]
Abstract
The vertical distribution of 35 volatile organic compounds (VOCs) was investigated in soil columns from two obsolete industrial sites in Eastern China. The total concentrations of ΣVOCs in surface soils (0-20 cm) were 134-1664 ng g-1. Contamination of VOCs in surface soil exhibited remarkable variability, closely related to previous production activities at the sampling sites. Additionally, the concentrations of ΣVOCs varied with increasing soil depth from 0 to 10 m. Soils at depth of 2 m showed ΣVOCs concentrations of 127-47,389 ng g-1. Among the studied VOCs, xylene was the predominant contaminant in subsoils (2 m), with concentrations ranging from n.d. to 45,400 ng g-1. Chlorinated alkanes and olefins demonstrated a greater downward migration ability compared to monoaromatic hydrocarbons, likely due to their lower hydrophobicity. As a result, this vertical distribution of VOCs led to a high ecological risk in both the surface and deep soil. Notably, the risk quotient (RQ) of xylene in subsoil (2 m, RQ up to 319) was much higher than that in surface soil. Furthermore, distinct effects of VOCs on soil microbes were observed under aerobic and anaerobic conditions. Specifically, after the 30-d incubation of xylene-contaminated soil, Ilumatobacter was enriched under aerobic condition, whereas Anaerolineaceae was enriched under anaerobic condition. Moreover, xylene contamination significantly affected methylotrophy and methanol oxidation functions for aerobic soil (t-test, p < 0.05). However, aromatic compound degradation and ammonification were significantly enhanced by xylene in anaerobic soil (t-test, p < 0.05). These findings suggest that specific VOC compound has distinct microbial ecological effects under different oxygen content conditions in soil. Therefore, when conducting soil risk assessments of VOCs, it is crucial to consider their ecological effects at different soil depths.
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Affiliation(s)
- Meng Gao
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Xuelin Li
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Qiuyue Zhang
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Siyuan Li
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Shanxing Wu
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
| | - Yu Wang
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China.
| | - Hongwen Sun
- MOE Key Laboratory of Pollution Processes and Environmental Criteria, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China
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Ding X, Wei C, Wei Y, Liu P, Wang D, Wang Q, Chen X, Song X. Field test of thermally activated persulfate for remediation of PFASs co-contaminated with chlorinated aliphatic hydrocarbons in groundwater. WATER RESEARCH 2024; 249:120993. [PMID: 38086203 DOI: 10.1016/j.watres.2023.120993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 11/19/2023] [Accepted: 12/07/2023] [Indexed: 01/03/2024]
Abstract
The co-occurrence of per- and polyfluoroalkyl substances (PFASs) and chlorinated aliphatic hydrocarbons (CAHs) in groundwater has drawn increased attention in recent years. No studies have been conducted concerning the oxidative degradation of PFASs and/or CAHs by in situ thermally activated persulfate (TAP) in groundwater, primarily due to the difficulty in cost-effectively achieving the desired temperature in the field. In this study, the effects and mechanisms of PFASs degradation by in situ TAP at a site with PFASs and CAHs co-contaminants were investigated. The target temperature of 40.0-70.0 °C was achieved in groundwater, and persulfate was effectively distributed in the demonstration area - the combination of which ensured the degradation of PFASs and CAHs co-contaminants by in situ TAP. It was demonstrated that the reductions of perfluoroalkyl carboxylic acids (PFCAs) concentration in all monitoring wells were in the range of 43.7 %-66.0 % by in situ TAP compared to those maximum rebound values in groundwater, whereas no effective perfluoroalkane sulfonic acids (PFSAs) degradation was observed. The conversion of perfluoroalkyl acids (PFAAs) precursors was one of the main factors leading to the increase in PFCAs concentrations in groundwater during in situ TAP. CAHs were effectively degraded in most monitoring wells, and furthermore, no inhibitory effects of CAHs and Cl- on the degradation of PFASs were observed due to the presence of sufficient persulfate. Additionally, there were significant increases in SO42- concentrations and reductions of pH values in groundwater due to in situ TAP, warranting their long-term monitoring in groundwater. The integrated field and laboratory investigations demonstrated that the reductions in PFCAs and CAHs concentrations can be achieved by the oxidative degradation of in situ TAP.
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Affiliation(s)
- Xiaoyan Ding
- Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China; Institute of Eco-Environmental Research, Guangxi Academy of Sciences, Nanning 530007, China
| | - Changlong Wei
- Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
| | - Yunxiao Wei
- BCEG Environmental Remediation Co., Ltd., Beijing 210093, China
| | - Peng Liu
- BCEG Environmental Remediation Co., Ltd., Beijing 210093, China
| | - Dixiang Wang
- BCEG Environmental Remediation Co., Ltd., Beijing 210093, China
| | - Qing Wang
- Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xing Chen
- China Construction Eighth Engineering Division Corp., Ltd, Shanghai 200122, China
| | - Xin Song
- Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
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5
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Chang SH, Lin CW, Cheng YS, Liu SH. Effects of biodegradation, biotoxicity and microbial community on biostimulation of sulfolane. CHEMOSPHERE 2023; 319:138047. [PMID: 36739988 DOI: 10.1016/j.chemosphere.2023.138047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 01/25/2023] [Accepted: 02/02/2023] [Indexed: 06/18/2023]
Abstract
To evaluate the effectiveness of biostimulation in remediating soil-free groundwater and groundwater with soil, experiments were conducted using soil and groundwater samples that were contaminated with sulfolane. The main objective was to characterize the differences in sulfolane removal efficiency and biotoxicity between in situ soil-free groundwater and groundwater with soil and different concentrations of dissolved oxygen (1 mg/L and 5 mg/L) and various nutrient salts (in situ and spiked). Optimizing the nutrient salt conditions improved the removal efficiency of sulfolane by 1.8-6.5 that under in situ nutrient salt conditions. Controlling the dissolved oxygen concentration enhanced the efficiency of removal of sulfolane by 1.5-4.5 times over that at the simulated in situ dissolved oxygen concentration, suggesting that the degradation of sulfolane by indigenous microorganisms requires nutrient salts more than it requires dissolved oxygen. Biotoxicity data showed that the luminescence inhibition of Aliivibrio fischeri by sulfolane was lower in the biostimulated samples than in the pre-treated samples. Biostimulation reduced the biotoxicity of the treated samples by 42-51%, revealing that it was effective in removing sulfolane and reducing biotoxicity. Microbial community analysis showed that the biostimulation did not change the dominant species in the original in situ community, and increased the proportion of sulfolane-degraders. The outcome of this study can be used to set parameters for the remediation of groundwater that is contaminated by sulfolane in oil refineries.
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Affiliation(s)
- Shao-Heng Chang
- Department of Safety, Health and Environmental Engineering, National Yunlin University of Science and Technology, Yunlin, 64002, Taiwan, ROC
| | - Chi-Wen Lin
- Department of Safety, Health and Environmental Engineering, National Yunlin University of Science and Technology, Yunlin, 64002, Taiwan, ROC; Graduate School of Engineering Science and Technology, National Yunlin University of Science and Technology, Yunlin, 64002, Taiwan, ROC
| | - Yu-Shen Cheng
- Department of Chemical and Materials Engineering, National Yunlin University of Science and Technology, Yunlin, 64002, Taiwan, ROC; Bachelor's Program in Industrial Technology, National Yunlin University of Science and Technology, Yunlin, 64002, Taiwan, ROC
| | - Shu-Hui Liu
- Department of Safety, Health and Environmental Engineering, National Yunlin University of Science and Technology, Yunlin, 64002, Taiwan, ROC.
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6
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Fu XZ, Wu J, Li J, Ding J, Cui S, Wang XM, Wang YJ, Liu HQ, Deng X, Liu DF, Li WW. Heavy-metal resistant bio-hybrid with biogenic ferrous sulfide nanoparticles: pH-regulated self-assembly and wastewater treatment application. JOURNAL OF HAZARDOUS MATERIALS 2023; 446:130667. [PMID: 36580783 DOI: 10.1016/j.jhazmat.2022.130667] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 12/19/2022] [Accepted: 12/22/2022] [Indexed: 06/17/2023]
Abstract
Self-assembled bio-hybrids with biogenic ferrous sulfide nanoparticles (bio-FeS) on the cell surface are attractive for reduction of toxic heavy metals due to higher activity than bare bacteria, but they still suffer from slow synthesis and regeneration of bio-FeS and bacterial activity decay for removal of high-concentration heavy metals. A further optimization of the bio-FeS synthesis process and properties is of vital importance to address this challenge. Herein, we present a simple pH-regulation strategy to enhance bio-FeS synthesis and elucidated the underlying regulatory mechanisms. Slightly raising the pH from 7.4 to 8.3 led to 1.5-fold higher sulfide generation rate due to upregulated expression of thiosulfate reduction-related genes, and triggered the formation of fine-sized bio-FeS (29.4 ± 6.1 nm). The resulting bio-hybrid exhibited significantly improved extracellular reduction activity and was successfully used for treatment of high-concentration chromium -containing wastewater (Cr(VI), 80 mg/L) at satisfactory efficiency and stability. Its feasibility for bio-augmented treatment of real Cr(VI)-rich electroplating wastewater was also demonstrated, showing no obvious activity decline during 7-day operation. Overall, our work provides new insights into the environmental-responses of bio-hybrid self-assembly process, and may have important implications for optimized application of bio-hybrid for wastewater treatment and environmental remediation.
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Affiliation(s)
- Xian-Zhong Fu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China; Department of Biomedical Sciences, City University of Hong Kong, 999077, Hong Kong, China
| | - Jie Wu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Jie Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Jian Ding
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Shuo Cui
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Xue-Meng Wang
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Yun-Jie Wang
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Hou-Qi Liu
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Xin Deng
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China; Department of Biomedical Sciences, City University of Hong Kong, 999077, Hong Kong, China
| | - Dong-Feng Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China.
| | - Wen-Wei Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei 230026, China; University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China.
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7
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Ali M, Song X, Wang Q, Zhang Z, Che J, Chen X, Tang Z, Liu X. Mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX mixed contaminants in soil by native microbial consortium. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2023; 318:120831. [PMID: 36509345 DOI: 10.1016/j.envpol.2022.120831] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 11/29/2022] [Accepted: 12/04/2022] [Indexed: 06/17/2023]
Abstract
Despite the co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX) in the field, to date, knowledge on the bioremediation of benzene and benzo[a]pyrene (BaP) mixed contaminants is limited. In this study, the mechanisms underlying the biodegradation of benzene and BaP under individual and co-contaminated conditions followed by the enhanced biodegradation using methanol, ethanol, and vegetable oil as biostimulants were investigated. The results demonstrated that the benzene biodegradation was highly reduced under the co-contaminated condition compared to the individual benzene contamination, whereas the BaP biodegradation was slightly enhanced with the co-contamination of benzene. Moreover, biostimulation significantly improved the biodegradation of both contaminants under co-contaminated conditions. A trend of significant reduction in the bioavailable BaP contents was observed in all biostimulant-enhanced groups, implying that the bioavailable BaP was the preferred biodegradable BaP fraction. Furthermore, the enzymatic activity analysis revealed a significant increase in lipase and dehydrogenase (DHA) activities, as well as a reduction in the catalase and polyphenol oxidase, suggesting that the increased hydrolysis of fats and proton transfer, as well as the reduced oxidative stress, contributed to the enhanced benzene and BaP biodegradation in the vegetable oil treatment. In addition, the microbial composition analysis results demonstrated that the enriched functional genera contributed to the increased biodegradation efficiency, and the functional genera in the microbial consortium responded differently to different biostimulants, and competitive growth was observed in the biostimulant-enhanced treatments. In addition, the enrichment of Pseudomonas and Rhodococcus species was noticed during the biostimulation of benzene and BaP co-contamination soil, and was positively correlated with the DHA enzyme activities, indicating that these species encode DHA genes which contributed to the higher biodegradation. In conclusion, multiple lines of evidence were provided to shed light on the mechanisms of biostimulant-enhanced biodegradation of PAHs and BTEX co-contamination with native microbial consortiums.
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Affiliation(s)
- Mukhtiar Ali
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xin Song
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Qing Wang
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China
| | - Zhuanxia Zhang
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jilu Che
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China
| | - Xing Chen
- China Construction 8th Engineering Division Corp., LTD, Shanghai, 200122, China
| | - Zhiwen Tang
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Xin Liu
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China
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8
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Zhang K, Zhu Z, Peng M, Tian L, Chen Y, Zhu J, Gan M. Enhancement of Cr(VI) reduction by indigenous bacterial consortia using natural pyrite: A detailed study to elucidate the mechanisms involved in the highly efficient and possible sustainable system. CHEMOSPHERE 2022; 308:136228. [PMID: 36041522 DOI: 10.1016/j.chemosphere.2022.136228] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 07/28/2022] [Accepted: 08/24/2022] [Indexed: 06/15/2023]
Abstract
Pyrite was applied to Cr(VI) bioremediation as an inorganic electron donor due to the ability to provide electrons, while the role of pyrite in Cr(VI) bioremediation where organics as electron donors remains unknown. Herein a pyrite-based Cr(VI) bioreduction process in the sediment system containing lactate was demonstrated to be effective to detoxify Cr(VI): over 2200 mg L-1 Cr(VI) was continuously removed within 210 h with high reactivity (10.5 mg/(L·h)) all along. High-throughput 16S rDNA gene sequencing indicated that the pyrite could shape a functioning community that electrochemically active bacteria dominated (such as Fusibacter sp. and Rhodobacteraceae) instead of iron-oxidizing bacteria and sulfur-oxidizing bacteria. Mineralogy analysis results indicated that Fe(III), S22- and S0 formed on the pyrite surface after the oxidation of Cr(VI) might serve as the electron acceptor of microflora, then the S2- and Fe(II) with strong Cr(VI) reduction ability were formed by microbial reduction to enhance the removal of Cr(VI). This study provides new insights into thoroughly understanding the role of pyrite in the practical application of Cr(VI) bioreduction.
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Affiliation(s)
- Ke Zhang
- School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha, 410083, China
| | - Zhenyu Zhu
- Faculty of Agriculture, Forestry and Food Engineering, Yibin University, Yibin, 644000, China
| | - Mingxian Peng
- School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha, 410083, China
| | - Luyan Tian
- School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha, 410083, China
| | - Yaozong Chen
- School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha, 410083, China
| | - Jianyu Zhu
- School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha, 410083, China.
| | - Min Gan
- School of Minerals Processing and Bioengineering, Key Laboratory of Biohydrometallurgy of Ministry of Education, Central South University, Changsha, 410083, China.
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9
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Zhang B, Jiao W. Biochar facilitated bacterial reduction of Cr(VI) by Shewanella Putrefaciens CN32: Pathways and surface characteristics. ENVIRONMENTAL RESEARCH 2022; 214:113971. [PMID: 35952752 DOI: 10.1016/j.envres.2022.113971] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2022] [Revised: 06/29/2022] [Accepted: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Biochar can facilitate the microbial reduction of various pollutants in soil and groundwater environments, but its impact on Cr(VI) reduction by dissimilatory metal reducing bacteria (DMRB) remains to be systematically investigated. In this study, we prepared biochars at 500 °C and 700 °C from wheat straw and grass, and investigated the impact of these biochars on Cr(VI) reduction by a model DMRB, Shewanella Putrefaciens CN32 (CN32). Pristine biochars abiotically reduced Cr(VI), which decreased the concentration and toxicity of chromium to CN32 cells, and brought about higher overall Cr(VI) removal extent after CN32 were added sequentially; on the other hand, no enhancement effect were observed when biochars and CN32 were added simultaneously. Further tests between biologically reduced biochars and Cr(VI) revealed that the reaction rates between bioreduced biochars and Cr(VI) are relatively sluggish compared to that of direct Cr(VI) reduction by CN32, which prohibited biochars from directly accelerating the Cr(VI) reduction by CN32 in simultaneous-addition scenario. The relative importance of biochars' surface functional groups and surface areas on their reactivities towards Cr(VI) reduction were also investigated. This study deepened our understanding towards the role of biochar played during bacterial Cr(VI) reduction and could potentially contribute to optimizing the biochar-based Cr(VI) bioremediation strategies.
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Affiliation(s)
- Bo Zhang
- CAS Key Lab of Environmental Biotechnology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China
| | - Wentao Jiao
- State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China.
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10
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Zhang W, Zhu Y, Gu R, Liang Z, Xu W, Jat Baloch MY. Health Risk Assessment during In Situ Remediation of Cr(VI)-Contaminated Groundwater by Permeable Reactive Barriers: A Field-Scale Study. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2022; 19:ijerph192013079. [PMID: 36293661 PMCID: PMC9603126 DOI: 10.3390/ijerph192013079] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 10/06/2022] [Accepted: 10/08/2022] [Indexed: 05/19/2023]
Abstract
The presence of residual Cr(VI) in soils causes groundwater contamination in aquifers, affecting the health of exposed populations. Initially, permeable reactive barriers(PRB) effectively removed Cr(VI) from groundwater. However, as PRB clogging increased and Cr(VI) was released from upstream soils, the contamination plume continued to spread downstream. By 2020, the level of contamination in the downstream was nearly identical to that in the upstream. The study results show that during normal operation, the PRB can successfully remove Cr(VI) from contaminated groundwater and reduce the carcinogenic and non-carcinogenic risks to humans from the downstream side of groundwater. However, the remediated groundwater still poses an unacceptable risk to human health. The sensitivity analysis revealed that the concentration of the pollutant was the most sensitive parameter and interacted significantly with other factors. Ultimately, it was determined that the residual Cr(VI) in the soil of the study region continues to contaminate the groundwater and constitutes a serious health danger to residents in the vicinity. As remediated groundwater still poses a severe threat to human health, PRB may not be as effective as people believe.
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Affiliation(s)
- Wenjing Zhang
- Key Laboratory of Groundwater Resources and Environment, Jilin University, Ministry of Education, Changchun 130021, China
- College of New Energy and Environment, Jilin University, Changchun 130021, China
- Correspondence: ; Tel.: +86-057163743312
| | - Yifan Zhu
- Key Laboratory of Groundwater Resources and Environment, Jilin University, Ministry of Education, Changchun 130021, China
- College of New Energy and Environment, Jilin University, Changchun 130021, China
| | - Ruiting Gu
- School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
| | - Zhentian Liang
- Key Laboratory of Groundwater Resources and Environment, Jilin University, Ministry of Education, Changchun 130021, China
- College of New Energy and Environment, Jilin University, Changchun 130021, China
| | - Wenyan Xu
- Chemical Geological Prospecting Institute of Liaoning Province Co., Ltd., Jinzhou 121007, China
| | - Muhammad Yousuf Jat Baloch
- Key Laboratory of Groundwater Resources and Environment, Jilin University, Ministry of Education, Changchun 130021, China
- College of New Energy and Environment, Jilin University, Changchun 130021, China
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11
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Reductive Cr(VI) Removal under Different Reducing and Electron Donor Conditions—A Soil Microcosm Study. WATER 2022. [DOI: 10.3390/w14142179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Increased groundwater and soil contamination by hexavalent chromium have led to the employment of a variety of detoxification methods. Biological remediation of Cr(VI) polluted aquifers is an eco-friendly method that can be performed in situ by stimulating the indigenous microbial population with organic and inorganic electron donors. In order to study the effect of different redox conditions on microbial remediated Cr(VI) reduction to Cr(III), microcosm experiments were conducted under anaerobic, anoxic, and sulfate-reducing conditions and at hexavalent chromium groundwater concentrations in the 0–3000 μg/L range, with groundwater and soil collected from an industrial area (Inofyta region). As electron donors, molasses, emulsified vegetable oil (EVO), and FeSO4 were employed. To quantitatively describe the degradation kinetics of Cr(VI), pseudo-first-order kinetics were adopted. The results indicate that an anaerobic system dosed with simple or complex external organic carbon sources can lead to practically complete Cr(VI) reduction to Cr(III), while the addition of Fe2+ can further increase Cr(VI) removal rate significantly. Furthermore, Cr(VI) microbial reduction is possible in the presence of NO3− at rates comparable to anaerobic Cr(VI) microbial reduction, while high sulfate concentrations have a negative effect on Cr(VI) bioreduction rates in comparison to lower sulfate concentrations.
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12
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Shi X, He C, Wang Y, Lu J, Guo H, Zhang B. Concurrent anaerobic chromate bio-reduction and pentachlorophenol bio-degradation in a synthetic aquifer. WATER RESEARCH 2022; 216:118326. [PMID: 35364351 DOI: 10.1016/j.watres.2022.118326] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2021] [Revised: 03/16/2022] [Accepted: 03/17/2022] [Indexed: 06/14/2023]
Abstract
Chromate [Cr(VI)] and pentachlorophenol (PCP) coexist widely in the environment and are highly toxic to public health. However, whether Cr(VI) bio-reduction is accompanied by PCP bio-degradation and how microbial communities can keep long-term stability to mediate these bioprocesses in aquifer remain elusive. Herein, we conducted a 365-day continuous column experiment, during which the concurrent removals of Cr(VI) and PCP were realized under anaerobic condition. This process allowed for complete Cr(VI) bio-reduction and PCP bio-degradation at an efficiency of 92.8 ± 4.2% using ethanol as a co-metabolic substrate. More specifically, Cr(VI) was reduced to insoluble chromium (III) and PCP was efficiently dechlorinated with chloride ion release. Collectively, Acinetobacter and Spirochaeta regulated Cr(VI) bio-reduction heterotrophically, while Pseudomonas mediated not only Cr(VI) bio-reduction but also PCP bio-dechlorination. The bio-dechlorinated products were further mineralized by Azospira and Longilinea. Genes encoding proteins for Cr(VI) bio-reduction (chrA and yieF) and PCP bio-degradation (pceA) were upregulated. Cytochrome c and intracellular nicotinamide adenine dinucleotide were involved in Cr(VI) and PCP detoxification by promoting electron transfer. Taken together, our findings provide a promising bioremediation strategy for concurrent removal of Cr(VI) and PCP in aquifers through bio-stimulation with supplementation of appropriate substrates.
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Affiliation(s)
- Xinyue Shi
- School of Water Resources and Environment, MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China
| | - Chao He
- School of Water Resources and Environment, MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China; Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
| | - Ya'nan Wang
- School of Water Resources and Environment, MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China
| | - Jianping Lu
- School of Water Resources and Environment, MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China
| | - Huaming Guo
- School of Water Resources and Environment, MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China
| | - Baogang Zhang
- School of Water Resources and Environment, MOE Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China.
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13
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Gao Y, Wang H, Xu R, Wang YN, Sun Y, Bian R, Li W. Remediation of Cr(VI)-contaminated soil by combined chemical reduction and microbial stabilization: The role of biogas solid residue (BSR). ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2022; 231:113198. [PMID: 35033874 DOI: 10.1016/j.ecoenv.2022.113198] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 12/28/2021] [Accepted: 01/11/2022] [Indexed: 06/14/2023]
Abstract
In this work, the use of chemical reduction combined with microbial stabilization to remediate Cr(VI) in contaminated soil was systematically investigated. The effectiveness, phytotoxicity and microbial diversity resulting from the combination of ferrous sulfate with microbial stabilization by biogas solid residue (BSR) were determined. The stabilization experiments showed that the optimum Cr(VI) conversion rate of 99.92% was achieved with an Fe (II)/Cr(VI) molar ratio of 3:1, a BSR dose of 5.2% (wt), and a water content of 40%. Under these conditions, the residual Cr(VI) content was 0.80 mg/kg, which satisfied the risk screening value (≤ 5.7 mg/kg) for soil contamination of land for general development in China. The remaining Cr(VI) level was stable for 90 days during the chemical reduction and biogenic stabilization process. Moreover, Zucconi test analysis suggested that the soil phytotoxicity to Brassica campestris L. disappeared. The results of microbial diversity analysis indicated that the bacterial community changed significantly during chemical reduction and microbial stabilization processes, and Bacillus, Pseudomonas and Psychrobacter may participate in the reduction of Cr(VI) into Cr(III).
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Affiliation(s)
- Ying Gao
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China
| | - Huawei Wang
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China.
| | - Rong Xu
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China
| | - Ya-Nan Wang
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China
| | - Yingjie Sun
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China.
| | - Rongxing Bian
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China
| | - Weihua Li
- School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao, China
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Wang Q, Song X, Wei C, Jin P, Chen X, Tang Z, Li K, Ding X, Fu H. In situ remediation of Cr(VI) contaminated groundwater by ZVI-PRB and the corresponding indigenous microbial community responses: a field-scale study. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 805:150260. [PMID: 34537698 DOI: 10.1016/j.scitotenv.2021.150260] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Revised: 09/02/2021] [Accepted: 09/06/2021] [Indexed: 06/13/2023]
Abstract
The performance of a permeable reactive barrier (PRB) for the in situ remediation of hexavalent chromium [Cr(VI)] contaminated groundwater, and the resulted responses in the indigenous microbial community, were investigated in a field-scale study. The PRB consisted of a mixture of zero-valent iron (ZVI), gravel and sand. The results showed that the PRB segment with 20% active reaction medium (ZVI) was able to successfully reduce Cr(VI) via chemical reduction from 27.29-242.65 mg/L to below the clean-up goal of 0.1 mg/L, and can be scaled-up under field conditions. It was found that the ZVI induced significant changes in the indigenous microbial community structure and compositions in the area of the PRB and those areas downgradient. The competitive growth among Cr(VI)-reducing bacteria (the reduced abundance of Hydrogenophaga, Pseudomonas, Exiguobacterium and Rhodobacter, along with the enrichment of Rivibacter and Candidatus_Desulforudis) were observed in PRB. In addition, Cr(VI)-reducing bacteria (Hydrogenophaga, Pseudomonas, Exiguobacterium and Rhodobacter) were enriched in the downgradient of PRB, indicating that Cr(VI) can be further bio-reduced to Cr(III). The Cr(VI) bio-reduction could serve as a secondary mechanism for further removal of Cr(VI) from contaminated groundwater, suggesting that the actual lifetime of a PRB can be prolonged, which is important for the design and economic assessment of a PRB. Further analysis revealed that pH, dissolved oxygen, Cr(VI) level, the oxidation-reduction potential, and temperature were the main environmental factors influencing the subsurface microbial community compositions.
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Affiliation(s)
- Qing Wang
- CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; National Engineering Laboratory for Site Remediation Technologies, Beijing 100015, China
| | - Xin Song
- CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China.
| | - Changlong Wei
- CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
| | - Peng Jin
- EPCR Innovation and Technology LLC, PA 19406, USA
| | - Xing Chen
- CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
| | - Zhiwen Tang
- CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Kang Li
- NO.1 Institute of Geo-environment Survey of Henan, Henan 450003, China
| | - Xiaoyan Ding
- CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Heng Fu
- Nanjing Kangdi Environmental Protection Technology Co., LTD, Nanjing 21000, China
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15
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Biotic and Abiotic Biostimulation for the Reduction of Hexavalent Chromium in Contaminated Aquifers. WATER 2022. [DOI: 10.3390/w14010089] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Hexavalent chromium is a carcinogenic heavy metal that needs to be removed effectively from polluted aquifers in order to protect public health and the environment. This work aims to evaluate the reduction of Cr(VI) to Cr(III) in a contaminated aquifer through the stimulation of indigenous microbial communities with the addition of reductive agents. Soil-column experiments were conducted in the absence of oxygen and at hexavalent chromium (Cr(VI)) groundwater concentrations in the 1000–2000 μg/L range. Two carbon sources (molasses and EVO) and one iron electron donor (FeSO4·7H2O) were used as ways to stimulate the metabolism and proliferation of Cr(VI) reducing bacteria in-situ. The obtained results indicate that microbial anaerobic respiration and electron transfer can be fundamental to alleviate polluted groundwater from hazardous Cr(VI). The addition of organic electron donors increased significantly Cr(VI) reduction rates in comparison to natural soil attenuation rates. Furthermore, a combination of organic carbon and iron electron donors led to a longer life span of the remediation process and thus increased total Cr(VI) removal. This is the first study to investigate biotic and abiotic Cr(VI) removal by conducting experiments with natural soil and by applying biostimulation to modify the natural existing microbial communities.
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External Carbon Source Facilitates Indirect Cr (VI) Bioreduction Process by Anaerobic Sludge Produced from Kitchen Waste. SUSTAINABILITY 2021. [DOI: 10.3390/su13094806] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
This study presented the investigation on indirect Cr (VI) bioreduction process by anaerobic sludge produced from kitchen waste (ASKW) using an external source of glucose and sulfate to favor the reducing environment. These compounds were added at the beginning of the experiment along with 500 mg·L−1 Cr (VI). The system containing 1 g of glucose and 2 g of sulfate attained a higher reduction, which was 10% higher than that of the control experiment. This study indicated that a neutral environment (pH ~7), along with a high release of polysaccharides (PS), improved the removal efficiency by Cr (VI) bioreduction process. Desulfovibrio and Sulfurospirillum (genus level), which accounted for 3% and 1% of the whole microorganism, respectively, were responsible for the sulfidogenic reaction. Additionally, Thermovirga (genus level) reduced from 14% to 11% and 10%. These microorganisms contributed to dominating the indirect Cr (VI) bioreduction process. SEM and FTIR analysis of the sludges obtaining from the indirect Cr (VI) bioreduction systems indicated that the external glucose could facilitate the formation of looser porous structures and richer functional groups of sludges, thus adsorbing more Cr (III) to reduce its toxicity. Meanwhile, the intensity of the hydroxyl bond, which possesses strong reducibility, was much higher after adding external glucose. Chromate reductase gene (chrR) and sulfite reductase gene (dsrA) contributed to the indirect Cr (VI) bioreduction process. These might be the main mechanisms of the external glucose acting on indirect Cr (VI) bioreduction by ASKW.
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