Effect of biotic degradation of halogenated aliphatic compounds on zero-valent iron

A column study and batch experiments using microcosms were performed to analyze biotic reactions and their impact on the kinetic reaction rates of zero-valent iron during TCE degradation. In the biotic iron column study, ethylene formation as a by-product of the TCE degradation began decreasing gradually after 200 pore volumes. Cis-DCE became the sole DCE isomer observed in TCE degradation. These observations suggested that TCE degradation was largely the result of microbial activity. Iron participation in the TCE degradation decreased, probably due to reduced surface area available for iron reactivity. The application of ultrasonic energy to restore the reactivity of the iron surface was attempted at 600 pore volumes; however cis-DCE remained the sole by-product of TCE degradation.; Fifteen sets of microcosms were prepared to better understand the role of microbial metabolic groups involved in reductive dechlorination. A t-test at 95% confidence level was conducted to compare the first-order kinetic rates for each set of microcosms. Biotic activity did enhance kinetic rate of TCE degradation. Biotic sand microcosm had the highest kinetic rate constants with cis-DCE as the primary by-product. The biotic iron microcosm with high sulfates had the second highest kinetic rate constant for disappearance of TCE of 0.215 day−1 followed by the biotic iron microcosm with low sulfates at 0.193 day−1. The abiotic iron microcosms had the lowest average kinetic rate constant at 0.153 day−1 with ethylene as the primary byproduct for all iron containing microcosms.; Almost all of the microcosms with high sulfate concentration (100 mg/L) had a higher kinetic reaction rate than low sulfate concentration (2 mg/L) microcosms with the exception of those spiked with Molybdate to inhibit sulfidogen activity. While this difference was small (avg. 11%) it was statistically significant and may suggest that sulfidogens play a major role in TCE removal. Methane concentration was highest in biotic sand microcosm head space. Methane production appeared to be inhibited in all other biotic iron microcosms, probably due to elevated.