Effect of acetate and methanol on the kinetics of total dissolved selenium removal in a chemostat

BACKGROUND

Carbon source consumption in industrial bioreactors removing soluble Se contributes to the operating cost and can influence the rate of removal. This study used a laboratory chemostat to investigate the dependency of the rate of dissolved Se removal on the concentration of acetate and methanol, two carbon sources used in treatment of Se containing mine‐influenced water. It was hypothesized that the rate of dissolved Se removal follows a Monod kinetic model with carbon source as the limiting substrate.

RESULTS

A chemostat fed with 25 mg‐selenate‐Se/L and acetate as carbon source at different concentrations operated over a range of HRTs achieved maximal removal of 99.7% dissolved Se at an HRT of 1.5 days (rate of 16.7 mg‐Se/(L day)). When methanol was fed into the chemostat as the carbon source instead of acetate, the extent and rate of removal were much less (65% at an HRT of 6 days, rate of 2.7 mg‐Se/(L day)). Carbon source consumption per mole of dissolved Se removed was not constant and exceeded stoichiometric estimates. Monod kinetic parameters for the Dechloromonas/Ralstonia consortium growing on acetate were estimated as K_C= 3.36 mg‐C/ L and Y_X/C q_max,C= 0.70 1/day. The Methylophilaceae consortium growing on methanol did not exhibit Monod kinetic growth.

CONCLUSIONS

Using acetate as a carbon source achieved greater efficiency of dissolved Se removal than when methanol was used. Total dissolved Se removal rate was dependent on acetate only at low concentrations and when the HRT was close to washout. Whereas total dissolved Se removal rate was strongly dependent on HRT when methanol was used.

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