Cleaning of biologically fouled membranes with self-collapsing microbubbles.

Increasing global demand for water reclamation has driven the widespread development of membrane processes, where membrane biofouling due to microbial attachment onto membrane surfaces remains the biggest challenge. Given the potential ability of microbubbles (MBs) to generate pressure waves upon collapse, the responses of biofilms of different ages on nylon membrane surfaces towards self-collapsing air MBs was investigated. Changes in the fixed biomass, extracellular polysaccharides and proteins were determined for 3-h, 12-h, 18-h and 24-h old biofilms before and after treatment with MBs. The resistance-in-series model was further applied for analysis of various resistances after treatment of biofilms of different ages with MBs. The results showed substantial flux recovery 1 h after MB treatment for stationary phase biofilms in comparison with initial and exponential growth phase biofilms, which was consistent with the relatively larger percentage reduction in fixed biomass, extracellular polysaccharides and proteins for stationary phase biofilms. However, pore blocking still remained a big challenge even after treatment with MBs, regardless of biofilm age. The experimental data were further supported by confocal laser scanning microscope images. Collapsing MBs appear to be an alternative green chemical-free technology for mitigation of membrane biofouling.