Advanced sulfur biological denitrification: a systematic assessment of S/N ratio on microbial activity and nitrogen conversion

ABSTRACT

Figure shows the concept of study and its significance, operating conditions, reactors, sludge quality, relative abundance of microbial community, and how involves the sulfur driven denitrification mechanisms.

The present study investigated sulfur-driven autotrophic denitrification and sludge granulation in an integrated bioprocess reactor for sulfur, nitrogen, and phosphorus removal. Granular sludge was successfully cultivated in an upflow anaerobic sludge blanket (UASB) reactor under sulfur-oxidizing and nitrate-reducing conditions by gradually increasing the nitrogen loading rate. At a hydraulic retention time (HRT) of 8 h, the mature granular sludge achieved a nitrate removal efficiency of approximately 73%, with no detectable nitrite in the effluent. Fourier transform infrared analysis revealed the appearance of sulfur-related oxidized functional groups, indicating transformation of sulfur compounds during the denitrification process. Dynamic light scattering and scanning electron microscopy analyses demonstrated significant changes in biomass structure, including increased particle size and the formation of compact microbial aggregates. Microbial characterization of 21 cultivable isolates identified Pseudomonas aeruginosa (38%) as the dominant species, followed by Bacillus cereus (29%), Escherichia coli (14%), Chromobacterium violaceum (9%), Serratia spp. (5%), and Pseudomonas stutzeri (5%). The predominance of facultative nitrate-respiring microorganisms suggests the establishment of a specialized microbial consortium adapted to sulfur-rich and carbon-limited conditions. Overall, the results demonstrate that sulfur-driven autotrophic denitrification is a promising approach for nitrate removal from carbon-deficient wastewaters.