Dynamics of the nitrification and sulfide‐driven autotrophic denitrification processes in a single reactor using oxidation–reduction potential as an indicator of the process effectiveness

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Abstract BACKGROUND This paper evaluates the nitrification and sulfide‐driven autotrophic denitrification processes in a structured‐bed reactor subjected to recirculation and intermittent aeration (SBRRIA) applied to the post‐treatment of an anaerobic effluent. The SBRRIA reactor was operated during 130 days in which influent sulfide concentrations varied between 220.1 and 231.0 mg TDS L−1 (TDS, total dissolved solids). Temporal tests were performed to elucidate the dynamics and sulfide impacts on combined processes. RESULTS Sulfide partially inhibited the nitrifying activity, resulting in low NH4+‐N oxidation. This fact affected the overall nitrogen removal performance as total‐N removal efficiencies of 50 and 55% were attained in Conditions III and IV, respectively. On the one hand, under continuous aeration and in the absence of sulfide, the oxidation–reduction potential (ORP) reached 50 mV (versus Ag/AgCl) after 250 min of experiment. On the other, when sulfide was continuously provided in the feeding, the ORP was maintained lower than zero. Under anoxic conditions, the effective use of sulfide as an electron donor by autotrophic denitrification was verified by ORP monitoring. However, a concentration of 260 mg TDS L−1 associated with high pH proved inhibitory for NO3− reduction. CONCLUSIONS Based on the results obtained, new strategies of adding sulfide to the SBRRIA should be tested to minimize its inhibitory effect on nitrification and improve nitrogen removal in this unit. © 2018 Society of Chemical Industry

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