title: Fe0-based system as innovative technology for degrading trichloromethane: redox removal characteristics.
abstract: 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.
authors.affiliation: Department of Environmental Engineering and Science, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan. chliao@mail.chna.edu.tw
authors.forename: Chih-Hsiang
authors.initials: CH
authors.lastname: Liao
authors.forename: Chalermraj
authors.initials: C
authors.lastname: Wantawin
authors.forename: Ming-Chun
authors.initials: MC
authors.lastname: Lu
authors.forename: Chih-I
authors.initials: CI
authors.lastname: Huang
mesh_terms: 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
chemical_list: D012997:Solvents; D002713:Chlorine; D002725:Chloroform; D007501:Iron