Enhanced degradation of HCH in soil by synergetic alkaline hydrolysis and thermal activation of persulfate.

Purpose: Alkaline-thermal coupling activation of persulfate (PS) is an effective method for hexachlorocyclohexane (HCH) degradation. However, the process of this method requires high concentrations of NaOH and PS. Since HCH can be easily hydrolyzed into trichlorobenzene (TCB), in this study, we adopted the strategy of sequential addition of reagents (adding NaOH first and maintaining for 4 h before adding PS) and explored the effect of temperature and alkalinity on HCH hydrolysis and TCB oxidation, in order to develop a better degradation method for HCH which persists in the environment. Methods: Shake flask experiments were performed, which allowed for the examination of specific factors. The degradation of HCH was evaluated by measuring the concentrations of HCH and TCB during the reaction by gas chromatography. Results and discussion: It was found that high pH favored HCH hydrolysis but inhibited TCB oxidation. Almost no HCH degradation occurred under simultaneous addition (20 mM NaOH and 50 mM PS), while 80% of HCH was hydrolyzed within 4 h under sequential addition in soil. The results demonstrated that the concentration of alkali should be controlled and that sequential addition was more beneficial for the degradation of HCH, especially in the case of low alkali concentration. Moreover, the degradation efficiency was higher in soils with low soil organic matter (SOM) content, as SOM would affect PS and NaOH consumption and compete for radicals. Conclusion: This study provides practical information for future design of activated PS treatment for in situ remediation of HCH-contaminated environments. [ABSTRACT FROM AUTHOR]