THE EFFECT OF OXYGEN ON PERCHLORATE REDUCTION IN A BIOFILM REACTOR

Abstract

The purpose of this research was to investigate the effects of low concentration of oxygen on reduction of perchlorate, especially low perchlorate influent concentrations in a biofilm reactor, as well as the effect of flow pattern in a biofilm reactor. Dissolved oxygen averaging 1 mg/L did not inhibit reduction of influent perchlorate from 23 to 426 μg/L in the biofilm reactors when sufficient acetate was added, probably due to limitation of oxygen diffusion into the biofilm. Influent perchlorate ranging from 23 to 426 μg/L was reduced to below detection level (4 μg/L) in the presence of 1 mg/L dissolved oxygen (DO). Chloride was produced in a ratio of 0.37gCl-/gClO₄- and 0.35gCl-/gClO₄- in plug flow and recirculation biofilm reactor which is similar to stoichiometric amount (0.36gCl-/gClO₄-) indicating complete perchlorate reduction at 426 μg/L of ClO₄- feeding. At 23 μg/L influent perchlorate, total biomass solids were 3.18 g and 2.81 g in the plug flow and recirculation biofilm reactors. The most probable number (MPN) analysis for perchlorate-reducing bacteria showed 104 to 105 cells/cm2 in both biofilm reactors throughout the experiments. The effluent perchlorate concentrations were not significantly different in the two different flow regimes, plug flow and recirculation biofilm reactors.