Fe0-based system as innovative technology for degrading trichloromethane: redox removal characteristics.
BACKGROUND
The spent waste of aliphatic chlorinated solvents has caused severe deterioration of groundwater quality. Trichloromethane (TCM), which shows health and toxicological effects on human beings, was selected as a model compound to be dechlorinated through a redox system.


METHODS
The Fe0-based system including Fe0/H2O, Fe0/UV, Fe0/H2O2, and Fe0/UV/H2O2 was explored to evaluate its performance in dechlorinating TCM. H2O2 was dosed at later reaction time points to initiate Fenton or photo-Fenton reactions. The first two systems demonstrate the reductive dechlorination of TCM by Fe0-released electrons, while the latter two show dechlorination of TCM by both electron reduction and hydroxyl radical oxidation. The system parameters of TCM remaining, Cl- buildup, Fe2+ accumulation, H2O2 residue, and ORP were measured to describe different redox characteristics of TCM dechlorination. The Cl- buildup was used as a way to describe the degree of TCM dechlorination in an open reaction system.


RESULTS
Reductive dechlorination efficiencies of TCM were 5% and 6% for the systems of Fe0/H2O and Fe0/UV, respectively. In contrast, the Fe/H2O2 and Fe0/UV/H2O2 systems were capable of dechlorinating TCM reductively and oxidatively by 14% and 15%, respectively. The presence of UV light was found to retard the dissolution of Fe2+, but it enhanced the rate of chloride buildup, based on the comparison of Fe0/H2O and Fe0/UV systems. In addition, WV irradiation plays only a minor role in the Fe0/UV/H2O2 system, in view of TCM dechlorination. Application of small amount of H2O2 results in the increase of Fe2+ accumulation rate in the Fe0/H2O2 system.


CONCLUSIONS
TCM was dechlorinated mostly through post Fenton oxidation; reductive reaction represents a less efficient way to dechlorinate TCM. The efficiencies of overall TCM dechlorination for the two systems of Fe0/H2O2 and Fe0/UV/ H2O2 are comparable to each other, and this implies that the presence of UV irradiation imposes no significant enhancement. RECOMMENDATIONS AND OUTLOOKS: It is highly recommended to initiate effective redox dechlorination of TCM with the system of Fe0/H2O2, where the H2O2 in excess is applied at a later reaction time point.
Liao
Chih-Hsiang
CH
Department of Environmental Engineering and Science, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan. chliao@mail.chna.edu.tw
Wantawin
Chalermraj
C
Lu
Ming-Chun
MC
Huang
Chih-I
CI
D002713:Chlorine / Q000737:chemistry*; D002725:Chloroform / Q000737:chemistry*; D004787:Environmental Pollution / Q000517:prevention & control; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D012997:Solvents / Q000737:chemistry*; D014466:Ultraviolet Rays
D012997:Solvents; D002713:Chlorine; D002725:Chloroform; D007501:Iron