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

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 MnO 2 and NO 2 – was 122.28 kJ mol –1 in 298 K, suggesting that MnO 2 could not react with NO 2 – . 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 .