Enhancement of nitrification efficiency during sludge bulking by magnetic field under long sludge retention time

The aim of the present study is to investigate the potential of magnetic field application as an alternative approach for controlling sludge bulking due to long sludge retention time (SRT) while enhancing nitrification efficiency upon the occurrence. Two sequencing batch reactors, reactor A (SBR_A, magnetic field intensity 88.0 mT) and reactor B (SBR_B, control) were operated under long SRT to induce the growth of filamentous microorganisms. The effect of magnetic field on nitrification, viz. ammonia-nitrogen (NH₄-N) and nitrite removal, as well as biomass properties were studied under the sludge bulking condition. Results indicated that nitrification efficiency of SBR_A was consistently higher with 90% NH₄-N removal and 74-81% nitrite removal, which could be credited to the enhanced biomass properties of activated sludge due to the induced magnetic field. Metabolism activity and biodegradability of aerobic bacteria were also enhanced through the application of magnetic field, even under long SRT condition. This was evidenced by the average oxygen uptake rate (OUR) in SBR_A that was higher with 11.7 ± 1.2 mg/L·h compared to SBR_B with 9.5 ± 0.4 mg/L·h. Occurrence of filamentous sludge bulking was likewise minimized.