Effect of storage of NF membranes on fouling deposits and cleaning efficiency

The aim of this work was to investigate changes of the foulant deposit during storage and the impact of storage onto cleaning efficiency of a nanofiltration membrane. ATR-FTIR analysis and chemical cleaning tests were performed on membrane pieces cut from a NF spiral wound module extracted from a drinking water plant just after sampling or stored for 4 or 8 weeks in distilled water at 4°C. Membrane permeability of flat sheets was measured before and after cleaning with a cross flow lab-scale pilot. For the non stored membrane, an homogeneous biofouling deposit was observed on the membrane surface by ATR-FTIR analysis. During membrane storage, some heterogeneity between the spectra, corresponding to different areas of the membrane appeared. A decrease of IR signals of foulants was observed after the first 4 weeks of storage; thereafter the IR signals remained approximately the same. The membrane permeability of the fouled flat sheets increased slightly after 4 weeks and remained stable after 8 weeks of storage. After cleaning, the biofilm IR signals of the membrane samples analyzed immediately after sampling or stored for 4 weeks decreased significantly. Cleaning had no significant effects on the biofoulant deposit after a storage of 8 weeks. Increases in permeability of 10, 5, and 5% were obtained after cleaning of the fouled flat sheets not stored, stored for 4 or 8 weeks, respectively. In conclusion, the storage of fouled NF membrane cuts in distilled water at 4°C conducted to alterations of the biofouling deposit but was compatible with cleaning efficiency tests after a storage period of 4 weeks at the most.