Reduction of haloacetic acids by Fe-0: Implications for treatment and fate

To predict the fate of haloacetic acids (HAAs) in natural or engineered sys tems, information is needed concerning the types of reactions that these co mpounds undergo, the rates of those reactions, and the products that are fo rmed. Given that many drinking water distribution systems consist of unline d cast iron pipe, reactions of HAAs with elemental iron (Fe-0) may play a r ole in determining the fate of HAAs in these systems. In addition, zerovale nt iron may prove to be an effective treatment technology for the removal o f HAAs from chlorinated drinking water and wastewater. Thus, batch experime nts were used to investigate reactions of four trihaloacetic acids, trichlo roacetic acid (TCAA), tribromoacetic acid (TBAA), chlorodibromoacetic acid (CDBAA), and bromodichloroacetic acid (BDCAA), with Fe-0. All compounds rea dily reacted with Fe-0, and investigation of product formation and subseque nt disappearance revealed that the reactions proceeded via sequential hydro genolysis. Bromine was preferentially removed over chlorine, and TBAA was t he only compound completely dehalogenated to acetic acid. In compounds cont aining chlorine, the final product of reactions with Fe-0 was monochloroace tic acid. Halogen mass balances were 95-112%, and carbon mass balances were 62.6-112%. The pseudo-first-order rate constants for trihaloacetic acid de gradation were as follows: BDCAA (10.6 +/- 3.1 h(-1)) > COBAA(1.43 +/- 0.32 h(-1)) approximate to TBAA (1.41 +/- 0.28 h(-1)) much greater than TCAA (0 .08 +/- 0.02 h(-1)).