Controlling Dissolved Oxygen in Electrochemical Anammox Systems through Sodium Sulfite with Nitrogen Stripping

The long-term maintenance of low concentration of dissolved oxygen (DO) is an important condition for the enrichment of anammox bacteria (AnAOB) in the electrochemical anammox system (EAS). In this study, a new method to control DO by the combination of sodium sulfite with nitrogen stripping was attempted, and the influence of sodium sulfite concentration on the nitrogen removal performance was studied. The results show that under the optimal conditions (i.e., sodium sulfite concentration = 200 mg/L, nitrogen stripping time = 40-60 min, nitrogen flow = 350 mL/min), the DO in the water was controlled below 0.3 mg/L, which saves more than half of the time required for removing DO compared with the nitrogen stripping method (120-140 min). However, the total nitrogen removal rate (NRR) at the optimal current density of 0.10 mA/cm(2) decreased gradually, and the NRR was 0.0091, 0.0061, 0.0026, and 0.0006 g N/[L center dot d] at the sodium sulfite concentration of 0, 200, 400, and 600 mg/L, respectively. Simultaneously the specific anammox activity decreased from 0.0077 g N/[g VSS center dot d] to 0.0032 g N/[g VSS center dot d]. It is concluded that when the current density was 0.10 mA/cm(2) and the concentration of sodium sulfite was 200 mg/L, the optimal operating conditions were both anammox activity and deoxidation. Therefore, the combination of sodium sulfite with nitrogen stripping has great application potential to control DO in the EAS.