Effects of pH on dechlorination of trichloroethylene by zero-valent iron

The surface normalized reaction rate constants (k(sa)) of trichloroethylene (TCE) and zero-valent iron (ZVI) were quantified in batch reactors at pH v alues between 1.7 and 10. The k(sa) of TCE linearly decreased from 0.044 to 0.009 l/h m(2) between pH 3.8 and 8.0, whereas the k(sa) at pH 1.7 was mor e than an order higher than that at pH 3.8. The degradation of TCE was not observed at pH values of 9 and 10. The k(sa) of iron corrosion linearly dec reased from 0.092 to 0.018 l/h m(2) between pH 4.9 and 9.8, whereas it is s ignificantly higher at pH 1.7 and 3.8. The k(sa) of TCE was 30-300 times hi gher than those reported in literature. The difference can be attributed to the pH effects and precipitation of iron hydroxide. The k(sa) of TCE degra dation and iron corrosion at a head space of 6 and 10 mi were about twice o f those at zero head space. The effect was attributed to the formation of h ydrogen bubbles on ZVI, which hindered the transport the TCE between the so lution and reaction sites on ZVI. The optimal TCE degradation rate was achi eved at a pH of 4.9. This suggests that lowering solution pH might not expe dite the degradation rate of TCE by ZVI as it also caused faster disappeara nce of ZVI, and hence decreased the ZVI surface concentration. (C) 2001 Els evier Science B.V. All rights reserved.