Sulfide promotes nitrogen removal in anammox low-strength ammonium wastewater treatment system

Anammox has been widely used for denitrification from different wastewaters due to its low energy and carbon sources consumption. Nevertheless, the presence of nitrate in the effluent has been found to impede the enhancement of total nitrogen removal efficiency (TNRE). In this study, anammox was employed in conjunction with sulfur autotrophic denitrification (SAD) in order to enhance TNRE. During a long-term test in an UASB reactor with 30 mg L^-1 ammonium influent concentration, it was observed that sulfide facilitated both nitrate removal efficiency (NRE) and TNRE. Specifically, compared with 0 mg L^-1 sulfide addition, the NRE and TNRE were enhanced from 92.55% and 74.56% to 94.10% and 89.51%, respectively with 10 mg L^-1 sulfide. However, with sulfide concentration increased to 20 mg L^-1, 81.13% of TNRE was only found. Notably, the anammox performance was observed to enhancement when the sulfide level was reduced to 0 mg L^-1 again, the result indicated that the inhibitory effect of 20 mg L^-1 sulfides can be reversed. Further exploration revealed that sulfide not only suppressed the activity of nitrifying bacteria but also acted as electron donor, aiding the conversion of NO₃^--N to N₂ through SAD process, this made the nitrate in effluence as low as 2.31 mg L^-1. The results of microbiological analysis demonstrated that the population of microorganisms associated with SAD increased in response to the addition of sulfide. The findings suggested a potential equilibrium and collaboration between SAD and anammox to further increase TNRE in low-strength ammonium wastewater treatment.