Low-dose chlorite drives stable nitrite accumulation for partial denitrification.

Area of Science:

• Environmental Science
• Microbiology
• Chemical Engineering

Background:

• Partial denitrification (PD) is crucial for nitrogen removal but faces challenges in stable nitrite accumulation.
• Precise control techniques are needed for practical application of PD.

Purpose of the Study:

• To introduce and evaluate chlorite (ClO2-) as a novel regulatory factor for stable and efficient nitrite accumulation in PD.
• To optimize the PD process for enhanced nitrogen removal and assess its performance under various conditions.

Main Methods:

• A continuously operated PD biofilter was employed to assess chlorite's effectiveness.
• Metagenomic analysis and quantitative polymerase chain reaction (qPCR) were used to identify key microbial communities and gene expression.
• The PD/Anammox (PD/A) coupling process was utilized for final nitrogen removal.

Main Results:

• Chlorite addition at 1.00 mg/L ClO2- maximized nitrite accumulation rate (NTR) to 97.6%, reducing effluent nitrate-nitrogen (NO3--N) to 0.61 mg/L.
• The biofilter demonstrated rapid start-up (7 days), stable operation (>30 days), and sustained high NTR (>67.5%) across varied C/N ratios and short hydraulic retention times.
• Chlorite degraded into non-toxic chloride and oxygen, preventing secondary pollution. Key genera identified were Thauera, Simplicispira, and Flavobacterium.
• qPCR revealed chlorite upregulated nitrate reductase (nar) and downregulated nitrite reductase (nir) genes.

Conclusions:

• Chlorite is an effective regulatory factor for achieving stable and efficient nitrite accumulation in partial denitrification.
• The chlorite-regulated PD process offers rapid start-up, robust performance, and environmental safety, making it suitable for engineering applications.
• This study provides valuable insights for optimizing the partial denitrification/anammox (PD/A) process for enhanced wastewater treatment.