Effects of Seepage Velocity and Temperature on the Dechlorination of Chlorinated Aliphatic Hydrocarbons

The influence of seepage velocity and groundwater temperature on the dechlorination rates of trichloroethylene (TCE) and tetrachloroethylene (PCE) by zero-valent iron $\left({\mathrm{Fe}}^0\right)$ were investigated by running laboratory column tests at seepage velocities ranging from 31 to $\mathrm{1,884}\mathrm{m}∕\mathrm{year}$ at temperatures of 10 and $23°\mathrm{C}$ . By increasing the seepage velocity from 31 to $\mathrm{1,884}\mathrm{m}∕\mathrm{year}$ at $10°\mathrm{C}$ , there were approximately seven- and nine-fold increases in the normalized dechlorination rate constants $\left({\overline{k}}_{\mathrm{SA}}\right)$ of TCE and PCE, respectively. Similarly, a four-fold increase in the ${\overline{k}}_{\mathrm{SA}}$ of TCE and PCE was also observed at $23°\mathrm{C}$ when increasing the seepage velocity from 103 to $\mathrm{1,183}\mathrm{m}∕\mathrm{year}$ . Raising the groundwater temperature from 10 to $23°\mathrm{C}$ at a given seepage velocity resulted in 2.7 and 1.1 times increases in the TCE ${\overline{k}}_{\mathrm{SA}}$ and PCE ${\overline{k}}_{\mathrm{SA}}$ , respectively. With the application of the Arrhenius equation, activation energies of $70.3\mathrm{kJ}∕\mathrm{mol}$ for TCE and $38.6\mathrm{kJ}∕\mathrm{mol}$ for PCE dechlorination were determined, indicating domination of the electron transfer process over the mass transfer as a major rate-limiting step of the dechlorination reactions by ${\mathrm{Fe}}^0$ .