Enhanced denitrification performance via biochar-mediated electron shuttling in Pseudomonas guariconensis: mechanistic insights from enzymatic and electrochemical analyses

Area of Science:

• Environmental Microbiology
• Water Treatment Technologies
• Biogeochemistry

Background:

• Nitrogen pollution poses a significant threat to aquatic ecosystems.
• Biological denitrification is crucial for nitrogen removal in wastewater treatment plants (WWTPs).
• Pseudomonas guariconensis is a key denitrifying bacterium in WWTPs, forming symbiotic relationships with organic carbon substrates.

Purpose of the Study:

• To investigate the mechanism by which biochar enhances denitrification performance.
• To evaluate the impact of biochar on Pseudomonas guariconensis strain XYH-2.
• To explore biochar-bacteria synergism for optimizing nitrogen removal in wastewater.

Main Methods:

• Experimental addition of biochar (0.5% w/w) to cultures of Pseudomonas guariconensis.
• Measurement of nitrate-nitrogen (NO3--N) removal efficiency and N2O accumulation.
• Electrochemical characterization to assess electron transfer system activity (ETSA).
• Analysis of extracellular polymeric substances (EPS) and key denitrifying enzyme activities (NAR, NIR, NOR, N2OR).
• Structural characterization of N2OR to understand substrate binding.

Main Results:

• Biochar addition improved NO3--N removal from 39% to 94% within 16 hours.
• N2O accumulation was reduced by 81.7% (from 837 to 153 ppm).
• Biochar increased ETSA by 48.5% and enhanced redox currents, acting as an electron shuttle.
• Activities of nitrate reductase (+75.6%), nitrite reductase (+25.4%), nitric oxide reductase (+33.3%), and nitrous oxide reductase (+159.4%) were significantly elevated.
• Biochar induced conformational changes in N2OR, improving substrate binding and mitigating N2O.

Conclusions:

• Biochar acts as an effective electron shuttle, enhancing microbial denitrification.
• Biochar significantly improves nitrogen removal efficiency and reduces greenhouse gas emissions (N2O) in wastewater treatment.
• Biochar-bacteria synergism offers a promising strategy for advanced wastewater treatment and nitrogen management.