Weak magnetic field: A powerful strategy to enhance partial nitrification.

Area of Science:

• Environmental Science
• Microbiology
• Wastewater Treatment

Background:

• Partial nitrification (PN) coupled with anaerobic ammonium oxidation is a key technology for removing nitrogenous contaminants.
• Optimizing PN processes is crucial for efficient wastewater treatment.
• External magnetic fields are being explored for their potential to enhance biological wastewater treatment.

Purpose of the Study:

• To investigate the effect of external magnetic fields on the partial nitrification (PN) process.
• To determine the optimal magnetic field strength for enhancing PN.
• To evaluate the long-term impact of magnetic fields on PN microbial communities and functional gene expression.

Main Methods:

• Laboratory-scale experiments were conducted using varying magnetic field strengths (0-25 mT).
• Short-term batch tests and long-term continuous experiments were performed.
• Bacterial diversity, relative abundance of specific bacteria (Nitrosomonadaceae), and functional gene expression (KEGG) were analyzed.

Main Results:

• A 5 mT magnetic field showed the best enhancement of aerobic ammonium oxidizing bacteria (AOB) activity in PN.
• The positive effect of the 5 mT magnetic field was observed throughout all stages of the long-term PN process.
• Increased magnetic field strength led to decreased bacterial diversity, with a significant reduction in Nitrosomonadaceae abundance at higher strengths (25 mT).

Conclusions:

• A weak magnetic field (5 mT) effectively enhances AOB activity, facilitating the rapid start-up of the PN process.
• The magnetic field increases AOB activity by enhancing free ammonia transport into microbial cells, not by increasing AOB abundance.
• This study confirms that weak magnetic fields are a simple and reliable tool for accelerating PN processes in wastewater treatment.