Effect of nitrite and nitrate on sulfate reducing ammonium oxidation

The effects of nitrite and nitrate on the integration of ammonium oxidization and sulfate reduction were investigated in a self-designed reactor with an effective volume of 5 L. An experimental study indicated that the ammonium oxidization and sulfate reduction efficiencies were increased in the presence of nitrite and nitrate. Studies showed that a decreasing proportion of N/S in the presence of NO₂ ^- at 30 mg·L^-1 would lead to high removal efficiencies of NH₄ ⁺-N and SO₄ ^2--S of up to 78.13% and 46.72%, respectively. On the other hand, NO₃ ^- was produced at approximately 26.89 mg·L^-1. Proteobacteria, Chloroflexi, Bacteroidetes, Chlorobi, Acidobacteria, Planctomycetes and Nitrospirae were detected in the anaerobic cycle growth reactor. Proteobacteria was identified as the dominant functional bacteria removing nitrogen in the reactor. The nitritation reaction could promote the sulfate-reducing ammonium oxidation (SRAO) process. NH₄ ⁺ was converted to NO₂ and other intermediates, for which the electron acceptor was SO₄ ^2-. These results showed that nitrogen was converted by the nitrification process, the denitrification process, and the traditional anammox process simultaneously with the SRAO process. The sulfur-based autotrophic denitration and denitrification in the reactor were caused by the influent nitrite and nitrate.