Patent ID: 7972514

Claim:
A method for performing maintenance on a membrane having semi-permeable properties for normal operation based on pressure retarded osmosis (PRO), the membrane having a first side and a second side, said membrane upon its normal PRO operation being configured on its first side to receive a first type of water having a first concentration of dissolved substance(s) at a first and higher pressure of between about 4-30 bar, and on said second side to receive a second type of water having a second and lower concentration of dissolved substance(s) at a second and lower pressure, wherein during normal PRO operation water flows across the membrane from the second side to the first side, the method comprising: temporarily interrupting the normal operation of the membrane by introducing a volume of the second type of water on the first side of the membrane, and creating a backwash function from the first to the second side of the membrane by applying the higher pressure of the first side onto the volume of water of the second type.