Simultaneous nitrogen and sulfur removal through synergy of sulfammox, anammox and sulfur-driven autotrophic denitrification in a modified bioreactor enhanced by activated carbon

Anaerobic ammonium (NH4+ - N) oxidation coupled with sulfate (SO42-) reduction (sulfammox) is a new pathway for the autotrophic removal of nitrogen and sulfur from wastewater. Sulfammox was achieved in a modified up-flow anaerobic bioreactor filled with granular activated carbon. After 70 days of operation, the NH4+ - N removal efficiency almost reached 70%, with activated carbon adsorption and biological reaction accounting for 26% and 74%, respectively. Ammonium hydrosulfide (NH4SH) was found in sulfammox by X-ray diffraction analysis for the first time, which confirmed that hydrogen sulfide (H2S) was one of the sulfammox products. Microbial results indicated that NH4+ - N oxidation and SO42- reduction in sulfammox were carried out by Crenothrix and Desulfobacterota, respectively, in which activated carbon may operate as electron shuttle. In the 15NH4+ labeled experiment, 30N2 were produced at a rate of 34.14 μmol/(g sludge·h) and no 30N2 was detected in the chemical control group, proving that sulfammox was present and could only be induced by microorganisms. The 15NO3- labeled group produced 30N2 at a rate of 88.77 μmol/(g sludge·h), demonstrating the presence of sulfur-driven autotrophic denitrification. In the adding 14NH4+ and 15NO3- group, it was confirmed that NH4+ - N was removed by the synergy of sulfammox, anammox and sulfur-driven autotrophic denitrification, where the main product of sulfammox was nitrite (NO2-) and anammox was the main cause of nitrogen loss. The findings showed that SO42- as a non-polluting species to environment may substitute NO2- to create a new "anammox" process.