| Many drinking waters supplies are contaminated with perchlorate, a rocket-fuel component released from military and aerospace facilities. Although perchlorate concentrations in water supplies are low, typically 100 μg/L or less, perchlorate is thought to affect thyroid function at around 4-μg/L. Therefore, treatment is needed to remove perchlorate from drinking water.; My research centered on a hollow-fiber membrane biofilm reactor (MBfR) that removes low-level perchlorate to below 4-μg/L. The reactor is based on perchlorate-reducing bacteria (PCRB), which gain energy by reducing perchlorate to innocuous chloride. The MBfR is well suited for water treatment, as hydrogen is less expensive than organic donors and is non-toxic. The MBfR fibers deliver hydrogen to biofilms growing on their surfaces, allowing essentially 100% hydrogen utilization.; I studied a mixed-culture denitrifying MBfR, where nitrate served as a primary electron acceptor. The reactor initially reduced a small fraction of influent perchlorate, but that its efficiency improved to 99% over several weeks. Perchlorate removal was more sensitive than denitrification to the pH and to the medium, and nitrate slowed perchlorate reduction rates.; I isolated and identified a novel, autotrophic, hydrogen-oxidizing PCRB and determined its kinetic parameters. Chlorate, a perchlorate-reduction intermediate, was a strong inhibitor of perchlorate reduction and appeared to be a competitive inhibitor. Nitrate inhibition was weak and its inhibition was not competitive.; I used Denaturing Gradient Gel Electrophoresis (DGGE) and Fluorescent In-Situ Hybridization (FISH) to study the microbial ecology of four mixed-culture, denitrifying MBfRs with varying amounts of perchlorate. A Dechloromonas species was dominant in all reactors, with 14% abundance in the reactor without perchlorate, 22% abundance in the reactor with 100-μg/L perchlorate, and nearly 50% abundance in the reactor with 10-mg/L perchlorate.; An important finding was that oxygen also could serve as a primary acceptor for perchlorate reduction. Based on DGGE, ecology with oxygen was similar to the nitrate reactors, although the FISH revealed that the dominant species might be a closely related but distinct species.; Screening tests for a wide range of oxidized contaminants, including bromate, chromate, selenate, and dichloromethane, demonstrated the potential for removing a wide range of oxidized contaminants. |
