DECHLORINATION OF TETRACHLOROBIPHENYL BZ#77 WITH NANOSCALE Co/Fe

In this study,the dechlorination of polychlorinated biphenyl congener BZ#77 (3,3',4,4'-tetrachlorobiphenyl)in solution by nanoscale zero valent iron(ZVI or Fe)and its bimetallic systems Ni/Fe and Co/Fe was investigated under anaerobic conditions using gas chromatography-mass spectrometry(GC-MS)as the primary analytical method.Test runs of the dechlorination by nanoscale Co/Fe in a simulated BZ#77-contaminated sandy soil were described along with a brief discussion on the mechanisms of the dechlorination reaction.GC-MS data showed that the rates of dechlorination for BZ#77 at 10 mg·l-1 in ethanol/water mixed solution were 23.4%,68.6% and 74.2% with nanoscale Fe,Ni/Fe and Co/Fe,respectively,and Co/Fe was the best. When the initial pH was adjusted to acidic,complete dechlorination was accomplished within few hours with nanoscale Co/Fe,but the influences of solution ionic strength on the dechlorination were insignificant. The rate of dechlorination reached 11% after treating BZ#77 at a concentration of 100 mg·kg-1 in a sandy soil for 10 days,and the rate of dechlorination increased to 25% when adding organic solvent ethanol,but complete dechlorination was not realized.Experiments using isotope of hydrogen revealed that BZ#77 underwent step-wise dechlorination by nanoscale Co/Fe.Substitution of chlorine atoms of the biphenyl rings by hydrogen atoms was observed and the source of hydrogen was water in the medium.The final product of dechlorination was biphenyl.