Kinetics of chlorite dismutase in a perchlorate degrading reactor sludge

Abstract

Kinetics of chlorite dismutase (CD), the terminal enzyme involved in the perchlorate (ClO4 − ) reduction pathway, in a ClO4 −-degrading bioreactor are reported in this study. Enzyme activity was determined from dissolved oxygen released during disproportionation of chlorite (ClO2 − ). CD activity was in the range 29.8–36.4U/mg dry weight sludge, and kinetic constants Vmax and Km of the enzyme were 37.83U/mg dry weight and 0.28 mM, respectively. Among reactor operational conditions, enzyme activity was observed at pH 4.0–9.0, with an optimum at pH 6.0. Redox potential in the range –50 to +120mV and NaCl up to 3.5 g/L had no significant effect on CD activity. However, co-occurring pollutants such as ammonium at 10 ppm, nitrite at 50 ppm and EDTA at 100μMreduced CD activity substantially. The present study highlights ideal bioreactor conditions to avoid ClO2 − toxicity, while indicating the buffering potential of a mixed microbial system against inhibiting factors to maintain stable CD activity in bioreactors.