Electron buffer formation through coupling thiosulfate-dependent denitratation with anammox in a single-stage...

Area of Science:

• Environmental Microbiology
• Biotechnology
• Water Treatment Engineering

Background:

• Conventional nitrogen removal processes face challenges in efficiency and cost.
• Integrating thiosulfate-dependent denitratation with anaerobic ammonia oxidation (anammox) offers a promising single-stage approach.
• Understanding the interplay of key factors is crucial for optimizing this combined process.

Purpose of the Study:

• To investigate the feasibility and performance of a single-stage reactor combining thiosulfate-dependent denitratation and anammox.
• To identify and optimize critical operational parameters, specifically molar ratios of ammonium/nitrate and thiosulfate/nitrate.
• To elucidate nitrogen transformation pathways using isotope labeling and propose a mechanistic model.

Main Methods:

• Utilized a single-stage reactor system for simultaneous denitratation and anammox.
• Systematically varied molar ratios of ammonium/nitrate (NH₄⁺/NO₃^-) and thiosulfate/nitrate (S₂O₃^2-/NO₃^-).
• Employed a novel ¹⁵N isotope labeling technique to trace nitrogen transformation pathways.

Main Results:

• Achieved a maximum total nitrogen removal efficiency of 99.4%.
• Identified optimal molar ratios of NH₄⁺/NO₃^- at 0.75 and S₂O₃^2-/NO₃^- at 0.85 for peak performance.
• Proposed a 3-step nitrogen transformation model involving sulfur-oxidizing bacteria and anammox bacteria, highlighting the role of electron buffering from thiosulfate oxidation.

Conclusions:

• The combined thiosulfate-dependent denitratation and anammox process is highly effective for total nitrogen removal.
• Optimized molar ratios are critical for maximizing efficiency in single-stage reactors.
• The proposed N transformation pathways provide insights into the microbial mechanisms, supporting its potential for mainstream nitrogen removal applications.