Remediation of groundwater contaminated by chlorinated organic compounds using alkaline-activated persulfate

Abstract

This research assesses how effectively alkaline-activated persulfate removes 1,2-dichloroethane (1,2-DCA) and trichloroethylene (TCE) from groundwater, while examining the underlying mechanisms. The results show that while the degradation efficiency of 1,2-DCA (4.2 × 10-4 M) ranges from 42 to 96%, TCE (4.2 × 10-4 M) is completely degraded by persulfate (4.2 × 10-2 M) after 120 h. The alkaline conditions (pH > 11) improve the degradation of 1,2-DCA but hinder TCE breakdown, leading to the formation of vinyl chloride through dehydrochlorination of 1,2-DCA. The degradation patterns for 1,2-DCA and TCE align with pseudo-first-order kinetics. The highest rate constant for 1,2-DCA oxidation is 6.3 × 10-6 s-1 at pH 13 whereas the highest rate constant for TCE removal is 2.5 × 10-5 s-1 at pH 3. Electron paramagnetic resonance analysis reveals the presence of both SO4-· and ·OH in the alkaline-activated persulfate system. Although alkaline persulfate generates more sulfate radicals and highly oxidative hydroxyl radicals, the elevated pH reduces oxidation reduction potential (ORP), which limits contaminant removal. For each unit increase in pH, the ORP value decreases by approximately 49.9 mV. Additionally, the presence of chloride (0.05-0.40 M) and carbonate (0.01-0.27 M) diminishes the degradation rates of both pollutants, with carbonate having a more substantial inhibitory effect under alkaline conditions. When both 1,2-DCA and TCE are present, alkaline conditions suppress TCE degradation, and acidic conditions reduce 1,2-DCA removal. This study highlights the importance of pH, ORP, and anion interactions in the effectiveness of alkaline-activated persulfate in treating chlorinated organic compounds in groundwater.