Integrated Modeling and Lab-Scale Investigations Demonstrate the Impact of Sulfide on a Membrane Aerated Biofilm Reactor

An emerging innovation in the wastewater treatment field is the application of membrane aerated biofilm reactors (MABRs) as low-energy and small-footprint nitrogen removal technologies. MABRs use membranes supplied with oxygen to grow mixed-redox counter-diffusional biofilms that are advantageous for studies of coupled sulfur and nitrogen cycling. We have previously shown that sulfide can induce dissimilatory nitrite reduction to ammonia (DNRA) in an MABR. However, the implications of sulfide-induced DNRA on reactor performance have not been quantified, and the overall performance of a MABR treating sulfide-ladened wastewater has not been evaluated. Here, we assessed the impact of sulfide on nitrogen removal in a MABR using modeling and experimental approaches. Experimentally, influent sulfide was increased stepwise into a methane-fed nitrifying MABR over 420 days, and microsensor profiling was used to quantify sulfide, nitrous oxide, and oxygen fluxes. Moderate increases in sulfide caused effluent ammonium concentrations to double and nitrous oxide emissions to increase a hundred-fold. Potential rates of DNRA were determined by calibrating a biofilm model to experimental data and were found to exceed nitrification rates at even moderate sulfide concentrations. The results described here highlight the importance of considering DNRA in engineered systems, especially when treating moderately sulfide-laden wastewaters.