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OuYang S, Li Y, Liu M, Zhao Q, Wang J, Xia J, He J, Jiang F. Elimination of methylmercury production potential in excessive sludge in wastewater treatment plants by sulfur addition. Sci Total Environ 2024; 915:169934. [PMID: 38199371 DOI: 10.1016/j.scitotenv.2024.169934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2023] [Revised: 12/20/2023] [Accepted: 01/03/2024] [Indexed: 01/12/2024]
Abstract
Mercury ions (Hg(II)) in wastewater can accumulate and transform into the highly neurotoxic methylmercury (MeHg) in activated sludge. The release of MeHg can have severe environmental consequences, making the treatment of MeHg-contaminated sludge a pressing concern. In this study, we found that all the collected activated sludge samples, from different wastewater treatment plants in four cities, had the potential for Hg methylation. The Hg-methylating capacity reached a maximum level of 0.70-0.92 μg/g volatile suspended solids after 48 h of exposure to 5 μg/L Hg(II) and showed an average MeHg production rate of 4.8±0.5%. Accordingly, a sludge treatment method involving the addition of elemental sulfur (S0) for a short-term or long-term duration (3 or 180 days, respectively) was proposed. The results demonstrated that this treatment approach effectively mitigated and potentially eliminated MeHg formation by simultaneously reducing Hg bioavailability and Hg-methylating bioactivity. We found that bioavailable Hg(II) ions were converted to a secondary phase similar to insoluble HgS after S0 addition treatment, leading to a decrease in Hg bioavailability in sludge. The enhancement of Hg and extracellular polymeric substances (EPS) complexation via the increasing amount of thiol groups in EPS also reduced the Hg bioavailability after the long-term treatment. Furthermore, the long-term S0 addition significantly reduced the abundance of Hg-methylators with hgcA gene and promoted the growth of Hg-reducers with merA gene, which ensured the complete elimination of MeHg production potential of the excessive activated sludge. Our findings demonstrated that the proposed S0-addition sludge treatment is a promising and safe biotechnology for treating Hg-contaminated sludge. This approach has the potential to contribute significantly to the mitigation of MeHg pollution within environmental contexts.
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Affiliation(s)
- Shenyu OuYang
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety, MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| | - Yu Li
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety, MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China.
| | - Ming Liu
- State Environmental Protection Key Laboratory of Urban Ecological Environment Simulation and Protection, South China Institute of Environmental Sciences, Ministry of Ecology and Environment of the People's Republic of China, Guangzhou 510655, China
| | - Qingxia Zhao
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety, MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| | - Jinting Wang
- Department of Civil and Environmental Engineering, Hong Kong University of Science & Technology, Hong Kong
| | - Juntao Xia
- School of Environmental Science & Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Junfeng He
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety, MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| | - Feng Jiang
- School of Environmental Science & Engineering, Sun Yat-sen University, Guangzhou 510275, China.
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Zhao Q, Wang J, OuYang S, Chen L, Liu M, Li Y, Jiang F. The exacerbation of mercury methylation by Geobacter sulfurreducens PCA in a freshwater algae-bacteria symbiotic system throughout the lifetime of algae. J Hazard Mater 2021; 415:125691. [PMID: 33773254 DOI: 10.1016/j.jhazmat.2021.125691] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 03/15/2021] [Accepted: 03/16/2021] [Indexed: 06/12/2023]
Abstract
Mine-polluted wastewater with mercury (Hg) poses severe environmental pollution since Hg(II) can be converted to highly neurotoxic methylmercury (MeHg) under anaerobic conditions. Previous studies on Hg methylation have focused on aquatic sediments, but few have investigated the MeHg formation in water layers containing algae. In this study, we investigated the dynamic effect of algae on Hg methylation throughout the lifetime of algae. We found that Chlorella pyrenoidosa was a non-methylating alga and exhibited good tolerance to Hg stress (1-20 μg/L); thus Hg(II) could not inhibit the process of eutrophication. However, the presence of C. pyrenoidosa significantly enhanced the Hg methylation by Geobacter sulfurreducens PCA. Compared to the control sample without algae, the MeHg production rate of algae-bacteria samples remarkably exacerbated by 62.3-188.3% with the algal growth period at cell densities of 1.5 × 106-25 × 106 cells/mL. The increase of algal organic matter and thiols with the algal growth period resulted in the exacerbation of MeHg production. The Hg methylation was also enhanced with the presence of dead algae, of which the enhancement was ~62.4% lower than that with the presence of live algae. Accordingly, the potential mechanism of Hg methylation in a freshwater algae-bacteria symbiotic system throughout the algal lifetime was proposed.
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Affiliation(s)
- Qingxia Zhao
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| | - Jinting Wang
- Department of Civil and Environmental Engineering, Water Technology Lab, Hong Kong Branch of Chinese National Engineering Research Center for Control & Treatment of Heavy Metal Pollution, The Hong Kong University of Science & Technology, Clear Water Bay, Kowloon, Hong Kong, China
| | - Shenyu OuYang
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
| | - Laiguo Chen
- State Environmental Protection Key Laboratory of Urban Ecological Environment Simulation and Protection, South China Institute of Environmental Sciences, Ministry of Ecology and Environment of the People's Republic of China, Guangzhou 510655, China
| | - Ming Liu
- State Environmental Protection Key Laboratory of Urban Ecological Environment Simulation and Protection, South China Institute of Environmental Sciences, Ministry of Ecology and Environment of the People's Republic of China, Guangzhou 510655, China
| | - Yu Li
- School of Environment, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China.
| | - Feng Jiang
- School of Environmental Science & Engineering, Sun Yat-sen University, Guangzhou 510275, China.
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