Enhanced effect of HAH on citric acid-chelated Fe(II)-catalyzed percarbonate for trichloroethene degradation

Abstract

This work demonstrates the impact of hydroxylamine hydrochloride (HAH) addition on enhancing the degradation of trichoroethene (TCE) by the citric acid (CA)-chelated Fe(II)-catalyzed percarbonate (SPC) system. The results of a series of batch-reactor experiments show that TCE removal with HAH addition was increased from approximately 57% to 79% for a CA concentration of 0.1 mM and from 89 to 99.6% for a 0.5 mM concentration. Free-radical probe tests elucidated the existence of hydroxyl radical (HO•) and superoxide anion radical (O2•-) in both CA/Fe(II)/SPC and HAH/CA/Fe(II)/SPC systems. However, higher removal rates of radical probe compounds was observed in the HAH/CA/Fe(II)/SPC system, indicating that HAH addition enhanced the generation of both free radicals. In addition, increased contribution of O2•- in the HAH/CA/Fe(II)/SPC system compared to the CA/Fe(II)/SPC system was verified by free-radical scavengers tests. Complete TCE dechlorination was indicated based on the total mass balance of released Cl- species. Lower concentrations of formic acid were produced in the later stages of the reaction for the HAH/CA/Fe(II)/SPC system, suggesting that HAH addition favors complete TCE mineralization. Studies of the impact of selected groundwater matrix constituents indicates that TCE removal in the HAH/CA/Fe(II)/SPC system is pH-dependent, with higher removal rates under acidic conditions. Although HCO3- was observed to have an adverse impact on TCE removal for the HAH/CA/Fe(II)/SPC system, the addition of HAH reduced its inhibitory effect compared to the CA/Fe(II)/SPC system. Finally, TCE removal in real groundwater was greater with the addition of HAH to the CA/Fe(II)/SPC system. The study results indicate that HAH amendment has potential to enhance effective remediation of TCE-contaminated groundwater.

Fundamentos e aplicação do percarbonato de sódio para remediação de solos e águas subterrâneas por oxidação química

“…Com isso, sugere-se que o radical principal na degradação do TCE foi o radical hidroxila, seguido pelo radical superóxido (FU et al 2018). O HA se mostrou mais eficiente para a remoção do TCE em concentrações de 2,25 mM, chegando em resultados expressivos de 99,6% de degradação do contaminante (FU et al 2017b). Desta forma, o uso do HAH contribuiu com o aumento do Fe(II) disponível em solução, produzindo mais radicais hidroxila.…”

“…Desta forma, o uso do HAH contribuiu com o aumento do Fe(II) disponível em solução, produzindo mais radicais hidroxila. Concentrações maiores de HA resultaram em menores valores de remoção, pois o próprio quelante pode se ligar as espécies oxidativas (FU et al 2017b(FU et al , 2018. Os efeitos de sequestro dos radicais gerados pelos íons cloreto e bicarbonato também foram observados (FU et al 2018).…”

“…Na maior parte das condições estudadas as principais espécies oxidativas identificadas foram o radical hidroxila e o ânion superóxido (DANISH et al 2016a, b;FU et al 2017bFU et al , 2018. O pH em meio ácido a próximo de neutro (3-5) associa-se a uma produção mais intensa de radicais hidroxila, enquanto em pH mais alcalino, a uma geração maior do radical ânion superóxido (DANISH et al 2016b).…”

The impact of surface properties and dominant ions on the effectiveness of G-nZVI heterogeneous catalyst for environmental remediation

“…Sodium percarbonate (Na 2 CO 3 .1.5H 2 O 2 , SPC) is a solid phase oxidant that has received tremendous attention owing to its potential as a substitute for hydrogen peroxide (H 2 O 2 ) for in-situ chemical oxidation (ISCO) processes (Danish et al, 2017a;Danish et al, 2016c;Fu et al, 2017). SPC is a preferred chemical oxidant compared to H 2 O 2 because it is easier and safer to be stored, handled, and transported, as well as effective over a wider range of pH.…”

“…Furthermore, aqueous Fe 2+ is relatively insoluble at pH ≥ 5 in many aquifer systems. Due to these limitations, a variety of chelating agents have been employed to enhance its solubility and availability, which leads to enrichment in degradation performance (Fu et al, 2017;Miao et al, 2015a;Miao et al, 2015b). However, the use of an additional reagent for in-situ applications increases costs and can initiates other issues, such as biodegradation of the reagent.…”