Effects of sulfur on nitrogen transformation in malodorous rivers with different remediations

High levels of total nitrogen (TN) in urban rivers remain a significant environmental concern due to their contribution to malodor, which needs an urgent solution. Considering the critical role of sulfur (S) in river habitats, how and to what extent S is involved in nitrogen (N) transformation deserves attention, especially in the context of river remediations. In this study, sediment incubation and river simulation showed that denitrification had a higher tolerance to sulfide than anaerobic ammonium oxidation (anammox) and outcompeted anammox in substrate competition. Moreover, appropriate levels of sulfide (40 mg·L^-1) stimulated S-driven autotrophic denitrification (SAD) activity (from 0.010 to 0.021 meq·g^-1 VSS·h^-1), with the relative abundances of Thiobacillus-like bacteria increasing from 0.46% to 21.51%. However, 40 mg·L^-1 sulfide inhibited anammox activity (from 0.010 to 0.0032 meq·g^-1 VSS·h^-1), with the decrease in both ammonium removal (from 55.25% to 22.32%) and anammox bacteria abundance (from 0.45% to 0.18%) in the incubation. A significant correlation (P < 0.01) between TN and sulfate was observed in calcium nitrate added and aerated river simulations, which indicated that sulfide was involved in the N-transformation through SAD. This finding was further confirmed by the relatively high abundances of Thiobacillus (1.15% and 1.12%, respectively) in both sediment aeration and calcium nitrate addition systems. Notably, S-driven autotrophic partial denitrification coupled with anammox was discovered under calcium nitrate addition. This study can fill the gap in understanding the interactions of S and N biogeochemical processes with river remediations and can help establish an effective approach for TN removal. KEY POINTS: • Anammox showed higher sensitivity to 40 mg·L^-1 sulfide than denitrification. • Coupling mechanisms between S and N were studied based on real river scenario. • Calcium nitrate induced the coupling of SAPD with anammox. • Denitrification showed relatively high tolerance to sulfide in malodorous rivers.