Abstract
This study explored the effect of 70-mT magnetic field on wastewater treatment capacity for activated sludge in long-term laboratory-scale experiments. Metagenomic sequencing were conducted based on Illumina HiSeq 2000 platform after DNA extraction of the activated sludge. Then the effect of the magnetic field on the microbial unigene and metabolic pathways in activated sludge was investigated. As a result, higher pollutant removal was observed at 70 mT, with which the elimination of total nitrogen (TN) was the most effective. Functional genes annotated based on eggNOG database showed that unigenes related to information storage and processing were enhanced by the magnetic field. For CAZy classification, category such as glycosyl transferases was more abundant in the reactor with magnetic field, which has been shown to promote the entire energy supply pathway. Additionally, in the KEGG categories, unigenes related to signaling molecules and interaction were significantly inhibited. Through the enrichment analysis of the nitrogen metabolism pathway, the magnetic field inhibited anabolic nitrate reduction by significantly inhibiting enzymes such as [EC:1.7.7.2], [EC:1.7.7.1], [EC:3.5.5.1], [EC:1.4.1.2] and [EC:4.2.1.1], which are related to the improvement of the denitrification ability. This study can provide insight for future research on the response mechanism of activated sludge to magnetic fields.
Highlights
This study explored the effect of 70-mT magnetic field on wastewater treatment capacity for activated sludge in long-term laboratory-scale experiments
Though the temperature changed with the seasons during the experiment, the wastewater treatment performance was more stable with the 70-mT magnetic field
Since the 70-mT magnetic field significantly promoted the removal of total nitrogen (TN), we focused on the analysis of the functional genes and pathways related to nitrogen metabolism of KEGG
Summary
This study explored the effect of 70-mT magnetic field on wastewater treatment capacity for activated sludge in long-term laboratory-scale experiments. The effect of the magnetic field on the microbial unigene and metabolic pathways in activated sludge was investigated. Others using magnetostatic device have found www.nature.com/scientificreports that the growth of activated sludge biomass and dehydrogenase activity positively affected by a 7-mT magnetic field. Our pre-experiments and previous studies on the external magnetic field at different intensities (70–150mT) confirmed that 70 mT has the most obvious improvement on the wastewater treatment performance and has significant influence on the activated sludge microbial community[13]. To fully reveal the mechanism of the magnetic field in improving the wastewater treatment performance, it is necessary to deeply study the microbial community structure and function in activated sludge
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