Influence of nitrite on the removal of Mn(II) using pilot-scale biofilters

Abstract

Two pilot-scale biofilters were used to systematically investigate the influence of nitrite on biological Mn(II) removal. Gibbs free energy change (ΔG) of the redox reaction between MnO2 and NO2– was 122.28 kJ mol–1 in 298 K, suggesting that MnO2 could not react with NO2–. When nitrite in the influent was increased from 0.05 to 0.5 mg L–1, manganese oxides did not react with nitrite in anaerobic conditions; nitrite was quickly oxidized and biological Mn(II) removal was slightly affected in 2 h in aerobic conditions. When nitrite was accumulated in the biofilter by increasing ammonia concentration, nitrite existed for more than 3 d and biological Mn(II) removal was affected in 3 d. When Mn(II) and ammonia in the influent were about 2 and 1.5 mg L–1, respectively, both of them were completely removed and the oxidation-reduction potential was increased with the depth of the filter from 16 to 122 mV. Biological Mn(II) removal followed the first-order reaction, and the k-value was 0.687 min–1.