Application of atmospheric pressure plasma jet in membrane bioreactor for membrane fouling control: Performance evaluation and mechanism exploration

The plasma plume generated by atmospheric pressure plasma jet (APPJ) can directly oxidize and decompose the sludge on the membrane surface in membrane bioreactor (MBR), and simultaneously modify the membrane surface, thus achieving the objective of membrane cleaning. Compared with NaClO cleaning, APPJ cleaning showed stronger performance in reducing membrane fouling. Furthermore, the average membrane fouling period using NaClO cleaning was 2.5 days, while that of APPJ cleaning increased to 3 days. The average total flux recovery ratio of the membrane after APPJ cleaning reached 85.6 %, which was higher than the 73.4 % after NaClO cleaning. The atmospheric pressure plasma plume could directly blow away the sludge on the membrane surface. Plasma generated reactive species, such as free radicals (•OH), H₂O₂ and O₃ to destroy cells and decompose extracellular polymers into small molecules. Meanwhile, the reactive species degraded β-D-glucose polysaccharide and caused the cake layer on the membrane to be looser. APPJ cleaning could degrade signal molecules C6-HSL in the cake layer, thereby maintaining C8-HSL at low levels. In addition, the direct scanning of the plasma jet to the membrane resulted in a more hydrophilic, smoother, and more electronegative surface, which increased the anti-fouling performance of the membrane.