Biocatalysts are a promising technology for water treatment due to their specificity, speed, and operation under environmentally relevant conditions. However, implementing biocatalyst reuse is critical for application in drinking water treatment. In this work, we investigated a modified biocatalyst, chlorite dismutase, that enables retention of the biocatalysts in a column for treatment of the disinfection byproduct, chlorite. Chlorite dismutase was modified to include an N-terminus Strep-Tag II facilitating the biocatalyst’s attachment to engineered streptavidin beads. Free and attached biocatalysts were tested in batch reactions. Chlorite decomposition rates were determined by measuring the end-product, oxygen, using a Clark-type electrode. In a column setup with the attached biocatalysts, breakthrough of chlorite was measured by monitoring for an increase in absorbance at 260 nm. Activities are reported in µmolchlorite min-1 µmol-1heme where heme is an indirect measure of the chlorite dismutase concentration. Observed activities were modeled using Michaelis-Menten kinetic and mass transfer equations. Free biocatalysts followed a traditional Michaelis-Menten kinetic profile with a maximum velocity (Vmax) of 39,311 µmolchlorite min-1 µmol-1heme and a half-saturation constant (Km) of 114 µM. Biocatalysts attached to beads showed decreased activity at low substrate concentrations compared to the free biocatalysts. This decrease in activity was accounted for by the mass transfer limitations imposed by the attachment; observed activity could be modeled by incorporating mass transfer and kinetics. Column treatment was tested over a range of chlorite concentrations from 1 to 80mM. Calculations based on column experiments of 1mg L-1 chlorite estimate greater than 1,000 bed volumes could be treated, exceeding the reuse threshold needed for the biocatalytic approach to be economically and environmentally viable relative to existing technologies.

Advancing biocatalytic applications in drinking water: Column treatment of the disinfection byproduct chlorite

255th National Meeting (2018)

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