The rapid conversion of sulphide may be explained by the low electron equivalent requirement for the oxidation of sulphide to elemental S0. The functional microbes preferred S2− to S0 as the electron donor, and S2− promoted the conversion of NO3− to N2, whereas NO3− and O2 caused S2− to form S0. When oxygen was used as an electron acceptor, the activity of sulphide oxidation to S0 was high, thus, a high S0 conversion rate is reasonable.