Abstract
This work presents an effective approach for manganese-doped Al2O3 ceramic membrane (Mn-doped membrane) fouling control by in-situ confined H2O2 cleaning in wastewater treatment. An Mn-doped membrane with 0.7 atomic percent Mn doping in the membrane layer was used in a membrane bioreactor with the aim to improve the catalytic activity toward oxidation of foulants by H2O2. Backwashing with 1 mM H2O2 solution at a flux of 120 L/m2/h (LMH) for 1 min was determined to be the optimal mode for in-situ H2O2 cleaning, with confined H2O2 decomposition inside the membrane. The Mn-doped membrane with in-situ H2O2 cleaning demonstrated much better fouling mitigation efficiency than a pristine Al2O3 ceramic membrane (pristine membrane). With in-situ H2O2 cleaning, the transmembrane pressure increase (ΔTMP) of the Mn-doped membrane was 22.2 kPa after 24-h filtration, which was 40.5% lower than that of the pristine membrane (37.3 kPa). The enhanced fouling mitigation was attributed to Mn doping, in the Mn-doped membrane layer, that improved the membrane surface properties and confined the catalytic oxidation of foulants by H2O2 inside the membrane. Mn3+/Mn4+ redox couples in the Mn-doped membrane catalyzed H2O2 decomposition continuously to generate reactive oxygen species (ROS) (i.e., HO• and O21), which were likely to be confined in membrane pores and efficiently degraded organic foulants.
Highlights
Ceramic membranes have been widely used in the membrane bioreactor (MBR) for wastewater treatment [1]
Organic foulants in wastewater gradually accumulate on the ceramic membrane surface and block membrane pores, causing severe membrane fouling [3]
We found that the ozone decomposition rate inside the membrane pores was about 428 times faster than that in the bulk phase, which was confirmed as a confinement effect of nano-scale membrane pores [20]
Summary
Ceramic membranes have been widely used in the membrane bioreactor (MBR) for wastewater treatment [1]. Manganese oxide-doped Al2 O3 ceramic membrane coupling with in-situ H2 O2 cleaning is expected to enhance the removal of organic foulants, providing a novel strategy to control membrane fouling. Another issue regarding in-situ chemical cleaning is the potential harm from the oxidants to the functional bacteria in activated sludge [18]. Al2 O3 ceramic membrane active layer is expected to bring about a double-win effect, both enhancing the membrane antifouling performance and promoting fouling mitigation via catalytic oxidation of organic foulants by H2 O2 within membrane pores. We discuss the fouling mitigation mechanisms in terms of surface properties, catalytic activity and the confinement effect of Mn-doped catalytic membranes
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