Sorption-mediated organohalide respiration biokinetics of tetrachloroethene

Combining microbial bioaugmentation and activated carbon sorbent amendment is an emerging approach for in situ remediation of recalcitrant organohalide-contaminated sediments. However, how sorbent surfaces impact the organohalide respiration rate of the attached microorganisms needs to be better understood to predict the efficacy of the technology and design optimized engineering solutions. Here, we carried out microcosm studies to measure organohalide respiration rates of tetrachloroethene by different bioaugmented solids. We demonstrate that biofilms of the halorespiring bacterium Dehalobium chlorocoercia strain DF-1, attached to activated carbons, graphite, and silica, maintain comparable biokinetics to their planktonic counterparts. The established model, developed with a combination of biokinetics, sorption kinetics, and competitive sorption effect, adequately described the aqueous concentrations of chloroethenes when considering sorption mass transfer. The bioavailability of B-vitamins is reduced through sorption to some sorbents, which can limit DF-1 biokinetics, indicating the importance of ensuring a sufficient concentration of the nutrients in the presence of sorbents. Additionally, the sorption of chloroethenes by the two activated carbons did not reduce net molar transformation even though aqueous concentration was suppressed, indicating potential inter-dynamics of concentrated chloroethenes between sorption and microbial dechlorination. Our work illustrates the importance of accounting for sorption effects in models better to characterize the bioremediation effectiveness of organochlorides via bioaugmented sorbents.