The effect of arsenite on denitrification using volatile fatty acids (VFAs) as a carbon source

Abstract

A lab-scale sequencing batch reactor (SBR) was operated at a solids retention time (SRT) of 20 ± 2.5 days to develop a consortium of denitrifying bacteria with a mean specific denitrification rate of 0.11 g nitrate (NO₃ ⁻-N)/g volatile suspended solids (VSS)/day. This biomass was used in a series of denitrification batch tests which used volatile fatty acids (VFAs) as their external carbon source. The VFAs were generated from an anaerobic digester that had an effluent VFA concentration of 5655 ± 876 mg/L (expressed as acetic acid (HAc)). The denitrification batch reactors were spiked with NO₃ ⁻-N (carbon-to-nitrogen (C:N) ratio of 3.0) and different concentrations of arsenite (a trivalent arsenic salt) in order to quantify the effect of arsenite on the denitrification process. A steady deterioration in the ability of the biomass to denitrify under increasing arsenite concentrations was observed with the mean specific denitrification rate dropping from 0.183 g NO₃ ⁻-N/gVSS/day at an arsenite concentration of 5 mg/L, to a value of 0.047 g NO₃ ⁻-N/gVSS/day at a concentration of 25 mg/L.

Keywords:

• Denitrification
• arsenic
• volatile fatty acids
• sequencing batch reactor

Acknowledgments

This research was sponsored by a research grant from the Civil and Natural Resources Department, the University of Canterbury, Christchurch, New Zealand. The first author is indebted to NZAID for providing a scholarship to study at the University of Canterbury. Both authors would like to thank Peter McGuigan and David MacPherson for their excellent technical assistance in this project.