Reverse Osmosis Biofilm Dispersal by Osmotic Back-Flushing: Cleaning via Substratum Perforation

We have demonstrated the application of osmotic back-flushing (OBF) for the removal of biofilms from reverse osmosis (RO) membranes and proposed a new biofilm dispersal mechanism. OBF was conducted in a laboratory-scale RO test cell by introducing a sequence of hypersaline solution (1.5 M NaCl) flushes into the feedwater, while still maintaining the applied hydraulic pressure (13.8 bar). OBF resulted in significant biofilm detachment, leaving a thin, perforated bacterial film (24 μm thickness) with vertical cavities ranging from 15 to 50 μm in diameter. Application of OBF led to significant reductionin the biovolume (70–79%) and substantial removal of total organic carbon and proteins (78 and 66%, respectively), resulting in 63% permeate water flux recovery. Our findings demonstrate the potential of this chemical-free RO membrane cleaning method while highlighting the possible challenges of the technique.