Complete removal of nitrate and nitrite by autotrophic denitrification in sulfur-limestone packed column reactor

Abstract

Removal of nitrogenous compounds (NO₃-N and NO₂-N) in autotrophic denitrification conditions was provided in a laboratory scale glass column reactor and the performance of this reactor was evaluated. Autotrophic microorganisms quickly acclimated and fully removed the NO₃-N after the first 6 days of operation. After reaching the steady state conditions, NO₂-N was introduced to the reactor with changing concentrations of between 4 and 20.0 mg/L. Nitrite was found to be an inhibitory compound that the effluent concentrations of both nitrite and nitrate increased. After a fluctuation period, they were 100 % removed except for 4 days which have concentrations below 5 mg/L. Sulfate was observed at the effluent and it was measured higher than the theoretically produced values. Average pH of the effluent was 7.5 when it was 8.0 in the feed. Alkalinity was also buffered with limestone particles in the reactor showing little difference (1 mg/L as CaCO₃) between the feed and the effluent. This study showed that sulfur-based autotrophic denitrification process was feasible to remove the nitrate and nitrite together after a proper adaptation period.