Biological degradation of cellulose acetate reverse‐osmosis membranes

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Abstract
An investigation has been carried out with the objective of relating losses in semipermeability of cellulose acetate (DS 2.5) reverse‐osmosis membranes to microbiological degradation (enzymic hydrolysis). Three sources of potentially destructive organisms were selected for study. One source was a set of degraded cellulose acetate reverse‐osmosis membranes; the other two sources were a surface soil sample and a lake bottom mud. From these, a total of 23 microbial isolates were obtained by culturing and enrichment. The isolates were characterized by staining and microscopic examination. Sterilized membranes were shaken continuously with sterile broths containing each isolate. In addition, membranes were placed on sterile agar and streaked with each isolate. Reverse‐osmosis testing of the membranes shaken in broth revealed losses in salt rejection of certain samples after 2 months. Visual observation of agar‐plated membranes showed complete degradation of several samples from each of the three sources of microorganisms. Infrared examination of degraded membranes showed up to 50% loss of acetyl content from the desalinating surface. No salt‐rejecting capability remained in these membranes. Cellulose triacetate membranes were resistant to degradation under conditions identical to those causing degradation of membranes having acetate DS of 2.3–2.5.

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