A comparative study on membrane fouling alleviation mechanisms by using nanoscale Fe₃O₄ and poly dimethyldiallylammonium chloride

ABSTRACT

Membrane bioreactor (MBR) has become a promising technology for wastewater treatment. However, membrane fouling frequently occurred which greatly increased operational expense. Two different membrane fouling alleviation mechanisms were explored in this study. Addition of poly dimethyldiallylammonium chloride (PDMDAAC) facilitated formation of flocs-flocs aggregates, which were more adaptable to the changing environment, resulting in less soluble microbial products (SMP) secretion. However, PDMDAAC lose activity gradually, and had a less sustainable effect on membrane fouling alleviation. Nanoscale Fe₃O₄ was applied to alleviate membrane fouling, and membrane sustainable filtration cycle extended 2-fold compared to the control group. Results showed that dehydrogenase activity in the reactor with optimal addition of nanoscale Fe₃O₄ increased 2.86 ± 0.11 times compared to control group. SMP (especially tryptophan protein-like substances) decreased to 9.79 ± 1.34 mg L⁻¹ with the addition of nanoscale Fe₃O₄, which was lower than that in the control group (15.31 ± 0.53 mg L⁻¹). It’s speculated that nanoscale Fe₃O₄ performed as conductive material, which intensified interspecies electron transfer. The sludge dehydrogenase activity was then enhanced, which facilitated the utilization and microbial degradation of SMP, suppressing membrane fouling consequently.

GRAPHICAL ABSTRACT

KEYWORDS:

• Membrane fouling
• nanoscale Fe₃O₄
• dehydrogenase activity
• soluble microbial products (SMP)
• interspecies electron transfer

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by National Natural Science Foundation of China [grant numbers 21776262 and 51708499] and China Postdoctoral Science Foundation [grant number 2017M612031]