Remediation of hexachlorocyclohexanes by cobalt-mediated activation of peroxymonosulfate

Abstract

Hexachlorocyclohexane isomers (HCHs) are one of the most ubiquitous and most easily detected organochlorine pesticides in environmental samples. This global distribution is enabled by HCH persistence. Moreover, HCH tends to bioaccumulate in human and animal adipose tissue. Since certain HCHs cause central nervous system, reproductive, and other endocrine damages, there is a necessity of a suitable remediation method to remove HCH from contaminated groundwater and soil. This study was conducted to evaluate the potential of peroxymonosulfate (Oxone) induced by cobalt salt (Co(NO₃)₂; Co(II)) to degrade HCHs. Cobalt(II) nitrate has been chosen instead of cobalt(II) chloride (which presents better activation properties for Oxone) in order to avoid an excess of chloride interference and more additional chlorination by-products. The optimal conditions (oxidant dose as well as cobalt dose) were determined for spiked water with HCH (0.85 μM of summed HCH isomers). Optimal oxidant dose was established by running a test with three different Oxone concentrations (molar ratio of Oxone:Co(NO₃)₂—1:0.1): 0.06, 0.6, and 6 mM. Degradation curves of summed HCH isomers were fitted into the pseudo-first-order kinetic model, and reaction rates are shown to be 0.03, 0.31, and 0.55 min⁻¹ for doses 0.06, 0.6, and 6 mM, respectively. Further experiments were carried out to determine the optimal Oxone:Co(NO₃)₂ molar ratio. Effectiveness of HCHs decontamination by Oxone:Co(NO₃)₂ in various molar ratios was in the order 1:0.1 > 1:1 > 1:0.01 > 1:0.001. It was observed that surplus of Co(NO₃)₂ can slow down the degradation rate constants. A reaction between sulfate radicals and Co(NO₃)₂ could be responsible for this phenomenon, which can lead to the formation of sulfate ions without HCHs oxidation. In addition, tests with higher HCH dose (close to the solubility limit) were carried out to determine by-products of decontamination. In these tests 2,4,6-trichlorophenol (2,4,6-TCP) was found to be the major intermediate of HCH isomers degradation. Trace levels of the trichlorobenzene (TCB), tetrachlorophenol (TeCP), and pentachlorophenol (PCP) were detected as well. The study revealed that Oxone induced by Co(II) shows a high degradation rate with HCH isomers, which can make it an attractive method for HCHs decontamination in the future.

Keywords:

• Hexachlorocyclohexanes
• HCH
• Chlorobenzenes
• Lindane
• Peroxymonosulfate
• Monopersulfate
• AOP
• Oxone

Acknowledgments

The research presented in this article was supported by the Ministry of Education, Youth and Sports in the framework of the targeted support of the “National Programme for Sustainability I” LO 1201 and the OPR&DI project “Centre for Nanomaterials, Advanced Technologies and Innovation,” CZ.1.05/2.1.00/01.0005.

The work was supported by the Ministry of Education of the Czech Republic within the SGS project no. 21066/115 on the Technical University of Liberec.

Notes

Presented at CEST2015 — 14th International Conference on Environmental Science and Technology, Rhodes, Greece, 3–5 September 2015