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Qinyuan Lu1, Junqing Zhou2, Ge Zhu2

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Biomass recirculation in Anoxic/Oxic (A/O) wastewater treatment hinders nitrification and denitrification. A two-stage vertical baffled bioreactor (VBBR) improves efficiency by separating microbial communities for better nitrogen removal.

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Area of Science:

  • Environmental microbiology
  • Wastewater treatment technologies
  • Bioreactor design

Background:

  • The Anoxic/Oxic (A/O) process recirculates mixed liquor to facilitate denitrification using nitrate from the oxic tank in the anoxic tank.
  • Biomass recirculation in A/O systems can lead to microbial community homogenization, potentially reducing nitrification and denitrification efficiencies.
  • Understanding microbial community dynamics is crucial for optimizing biological nutrient removal processes.

Purpose of the Study:

  • To investigate the impact of biomass recirculation on nitrification and denitrification rates in a simulated A/O process.
  • To compare the performance of a conventional A/O process with a two-stage vertical baffled bioreactor (VBBR) for total nitrogen removal.
  • To analyze the microbial community structure in response to biomass exchange and in different bioreactor configurations.

Main Methods:

  • Bench-scale experiments simulating biomass exchange (0-50%) between anoxic and oxic environments.
  • Phylogenetic analysis to characterize microbial community composition.
  • Performance evaluation of a two-stage VBBR against a conventional A/O process based on Chemical Oxygen Demand (COD) and Total Nitrogen (TN) removal.
  • Measurement of nitrification and denitrification rates.

Main Results:

  • Biomass exchange significantly reduced nitrification and denitrification rates, with a 50% exchange decreasing rates to 40% and 19% respectively.
  • Phylogenetic analysis confirmed increased microbial community similarity with higher biomass exchange ratios.
  • The two-stage VBBR achieved higher average COD (6%) and TN (22%) removal efficiencies compared to the conventional A/O process.
  • The VBBR demonstrated enhanced efficiency due to distinct microbial enrichments: denitrifying bacteria in the anoxic stage and nitrifying bacteria in the oxic stage.

Conclusions:

  • Biomass recirculation in conventional A/O systems negatively impacts nitrification and denitrification performance by homogenizing microbial communities.
  • The two-stage VBBR is a superior alternative, achieving efficient total nitrogen removal without biomass recirculation by maintaining distinct microbial populations.
  • VBBR's design promotes specialized microbial enrichment, leading to improved nutrient removal and reduced hydraulic retention time (HRT).