Improved biological wastewater treatment and sludge characteristics by applying magnetic field to aerobic granules

Abstract

Permanent magnets with non-uniform magnetic field and an electromagnet with 3–5 mT uniform magnetic field were applied to investigate their effects on both aerobic granulation and COD and ammonium removal in reactors with less than 7% coverage of magnetic field. It was found that both types of magnets had little influence on the granulation speed and the settling ability of granular sludge at the steady state. However, the maximum specific COD degradation rate and the maximum specific NH4+-N removal rate were increased by 45–54% and 30–50%, respectively, in the magnetic fields. Mean effluent COD with the electromagnet and the permanent magnet field, respectively, at the steady state, was 28 mg l?1 and 6 mg l?1, respectively, lower than the control at a statistical significance level of alpha = 0.05. No statistically significant increase in NH4+-N removal was observed at the steady state probably due to almost complete NH4+-N removal before the end of the cycle. In addition, it was found that extracellular polymeric substances in granular sludge with electromagnet were 77% more while soluble microbial products were much less compared with the control, suggesting a positively changed metabolism of granular sludge at steady state. The results in this study indicated that low-intensity magnetic field has a great potential to be applied in granular sludge for an improved wastewater treatment.

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Identifiers

ORCID for Yongqiang Liu: orcid.org/0000-0001-9688-1786

ORCID for Yeping Xiong: orcid.org/0000-0002-0135-8464

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