Most polymer membranes (e.g. flat sheet and spiral wound modules) are conditioned after manufacturing with a preservative agent (e.g. glycerol or sodium metabisulfite) to ensure storage stability. The membranes are usually also sealed in plastic bags with oxygen barrier and should only be unpacked before use. Most suppliers warranty up to 6 – 12 months of storage time for new membranes stored in their original packaging.
The following storage conditions are recommended:
Membranes should be cleaned after production and need to be stored wet. Storage can take place either inside the system or outside in closed containers or sealed bags. It is recommended to store the membranes in a preservative solution if they are not used for more than 1-2 days.
The following preservative solutions (in food-grade quality if required) may be used (chemical stability should be verified according to the suppliers’ spec sheet):
The storage conditions should comply with the ones described in the section Storage of new membranes. The preserved membrane should be inspected regularly for microbiological growth, and a pH measurement should be conducted. The storage solution must be exchanged as the circumstances require (e.g. observation of turbidity). Sodium metabisulfite may oxidize during storage, resulting in a pH decrease. The solution must be replaced at a pH of ≤ 3 to avoid membrane damages.
Ceramic membranes as well as certain types of hollow fiber and tubular membranes can be stored dry (please refer to membrane spec sheet).
Follow the steps below to store a membrane in the system:
After membrane storage it is recommended to flush the system and perform a CIP before starting the next production.