Isolation and characterization of a potential heterotrophic nitrifying–aerobic denitrifying and phosphorus-accumulating bacterium Pseudomonas putida S3 and its nutrient removal performance

ABSTRACT Efficient removal of nitrogen and phosphorus from wastewater with a low carbon-to-nitrogen (C/N) ratio is often constrained by limited carbon availability. Therefore, facultative microbial strains capable of both heterotrophic nitrification–aerobic denitrification and phosphorus accumulation are highly desirable, as they can enhance nutrient removal efficiency by maximizing carbon utilization within a single biological process. In this study, a multifunctional bacterium, Pseudomonas putida S3, was isolated from excess sludge collected from a municipal wastewater treatment plant. Batch experiments optimized their nutrient removal, with sodium citrate as the preferred carbon source, ammonium chloride as the nitrogen source, a C/N ratio of 6, and a nitrogen-to-phosphorus ratio of 15. Under aerobic conditions, strain S3 exhibited excellent simultaneous nitrogen and phosphorus removal. The observed removal of ammonia nitrogen, reaching 73.33%, together with a simultaneous 71.53% decrease in total nitrogen within 48 h under aerobic conditions, supports heterotrophic nitrification and suggests potential aerobic denitrification. Moreover, S3 achieved complete removal of phosphorus from the aqueous phase under aerobic conditions, accompanied by the intracellular formation of metachromatic granules. These findings highlight strain S3 as a promising microbial candidate for advanced treatment of low C/N wastewater and provide a theoretical basis for resource-oriented utilization of excess sludge.