Low-Frequency Infra-red electromagnetic wave promotes partial nitrification by affecting the community signal system

Abstract Ammonia oxidizing bacteria (AOB) are susceptible to environmental factors and compete with nitrite oxidizing bacteria, which seriously limits the stability of partial nitrification (PN). This study investigated the potential of applying low-frequency infra-red electromagnetic radiation to enhance the PN process. The electromagnetic wave (EMW) was evaluated at different intensities, and 0.06 μT EMW was found most effective in enhancing the activity of AOB. The long-term experiment indicated that the application of 0.06 μT EMW shortened the start-up period from over 15 to 10 days, and exhibited more stable to loading rate variation. Through the analysis of the microbial community composition, it was found that Nitrosomonas increased from 0.1% of inoculated sludge to 3.0% of the control reactor and 4.6% of EMW treated reactor. PN metabolic pathway was analyzed through metagenomics sequencing, and a model in which EWM promoted PN activity by affecting the community signal system was proposed: EWM increased the expression of specific genes through a two-component regulatory system and increased the activity of related enzymes by serine-threonine protein kinase. These findings implies that suitable EMW irradiation is efficient and economical for enhancing AOB activity and conducive for rapid start-up and stability of the PN process.