Abstract:
The impact of hydroxylamine hydrochloride (HAH) addition on the enhancement of trichloroethylene (TCE) degradation in the citric acid (CA)-chelated Fe
2+-catalyzed sodium percarbonate (SPC) system was investigated. The effects of HAH dosage and solution martirx (Cl
-, HCO
3- and hurmic acid) on TCE removal were examined and the results indicated that HAH promoted TCE degradation significantly by transferring Fe
3+ to Fe
2+, therefore maintaining a sustainable activation of Fe
2+. Under the optimum molar ratio of
nSPC:
nFe2+:
nTCE=5:3:1 at the initial concentration of TCE 0.15 mol/L and CA 0.50 mmol/L, the final TCE removal efficiency was 99.6%. HCO
3- had significant inhibitory effect on the degradation of TCE, whereas the effects of Cl
- and humic acid on the degradation of TCE could be ignored. In addition, TCE removal inhibition rate of HCO
3- were 59.9%, 15.5% and 14.9% respectively when HCO
3- concentration was all 1.0 mmol/L in SPC/Fe
2+/TCE, SPC/Fe
2+/CA/TCE and HAH/SPC/Fe
2+/CA/TCE systems. The results indicated that HAH alleviated HCO
3- inhibitory effect on the degradation of TCE. Scavengers tests were also conducted to understand the roles of ·OH and O
2-· on TCE degradation. The results showed that ·OH and O
2-· contributed 79.2% and 21.9% to TCE removal, respectively. The consistency of Cl
- concentration both experimentally and theoretically suggested the complete dechlorination of TCE in HAH/SPC/Fe
2+/CA/TCE system. The intermediate products were formic acid, NO
2- and NO
3-. The concentration of formic acid increased to 5.8 mg/L within 60 min and then decreased to 1.4 mg/L within 120 min, meaning that the addition of HAH favors further degradation of formic acid and therefore complete mineralization of TCE. The overall results strongly confirmed the benefits of HAH amendment to TCE degradation in the SPC/Fe
2+/CA system which provided a technical basis for practical applications in TCE contaminated groundwater remediation.