Inter- and intraspecies competitive effects in reactions of chlorinated ethylenes with zero-valent iron in column reactors

Reaction kinetics are a key component of process models used to design Fe(0 ) permeable barriers employed to treat groundwater contaminated with chlori nated solvents. In this work, columns packed with a mixture of zero-valent iron and glass microbeads were used to assess whether the competitive effec ts observed in batch systems also occur in column reactors. As with the bat ch studies previously conducted, both inter- and intraspecies competition w ere observed, in qualitative agreement with predictions obtained from a mod ified Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model in which spec ies compete for a limited number of reactive sites. The observed changes in pseudo first-order rate "constant" at different initial concentrations or in the presence of competitors could not be attributed to alterations in th e transport properties of the column packing or to "aging" of the iron. Num erical simulations were used to explore the consequences of applying a pseu do first-order kinetic model instead of the LHHW model. The results demonst rate that intraspecies competitive effects are sufficiently important to me rit explicit consideration in permeable barrier design.