Enhanced selective recovery of powder carrier-supported biofilms for enrichment of denitrifying functional bacteria

• Novel method assessed microbial distribution properties in activated sludge. • Differentiated distribution of denitrifying bacteria and PAOs has been achieved. • Segregation density threshold of biofilm from suspended sludge was 1.20 g/cm 3 . • Contradiction in the generation cycle of denitrifying bacteria and PAOs was resolved. • Effluent TN of M-IFAS (5.40 mg/L) group was lower than ASM group (9.70 mg/L). An innovative integrated fixed-film activated sludge (IFAS) system using high-concentration powder carriers was developed to promote microbial growth and optimize community distribution, achieving high efficiency denitrification in municipal wastewater. A critical challenge remains the efficient recovery of carrier biofilm from activated sludge. In this study, multi-layer density gradient centrifugation was employed to characterize the biochemical characteristics and microbial distribution patterns of sludge. Under the optimal cyclone inflow velocity of 3.5 ± 0.5 m/s, the aged cell can efficiently be detached from biofilm sludge via the cyclone separation unit, increased the proportion of live cells by 20%. The cyclone separation unit can also successfully separate suspended and biofilm sludge, enriching denitrifying bacteria in the underflow sludge and phosphate accumulating organisms (PAOs) in overflow sludge. Compared to overflow sludge, underflow sludge (biofilm) exhibited a 33% increase in particle size and a 0.51-fold increase in denitrification rate constants, leading to improvements of nitrogen and phosphorus removal efficiencies exceeding 73%. This study proposes a novel strategy for precise regulation of dual sludge ages, addressing the contradiction between the long generation cycles of denitrifying microorganisms and the short generation cycles of PAOs. These findings provide valuable insights for the targeted enrichment of denitrifying microorganisms within carrier biofilm, enhancing denitrification and phosphorus removal during the expansion and upgrading of municipal wastewater treatment plants.