THE GROWTH OF BIOLOGICAL FILMS ON REVERSE OSMOSIS MEMBRANES

While the body of lieturature suggests that the development of a biological film on the surface of reverse osmosis membranes is a contributing factor to membrane fouling, there have been little data to support this supposition. Experiments in this study were designed to test the hypothesis that the growth of a biofilm on reverse osmosis membrane do reduce the amount of water produced. Further objectives were to develop an understanding of the link between microbial population distributions and biofilm formation and to evaluate the relationship of environmental parameters and their effect on film formation.; Small scale test chambers were developed to approximate a reverse osmosis water treatment system. A freshwater seed of microorganisms containing a diverse population was used throughout the study. A comparison made between unsuppressed growth and growth suppressed with mercuric chloride as a biological inhibitor showed that the development of biofilm on reverse osmosis membranes can be a significant part of the fouling process. The addition of 30 mg/l of glucose as a nutrient source developed a biofilm that resulted in a 30 percent production decrease in four days compared to a 5 percent loss of production, under the same conditions, when the growth was inhibited.; It was found that the distribution of bacteria comprising the biofilm matrix was influenced by the amount of nutrient supplied. When the amount of glucose was increased from 10 to 300 mg/l, the amount of fermentative bacterial isolates from biofilms assayed increased from 7.3 to 100 percent of the bacteria tested.; The study of the relationship between the growth of the biofouling layer and temperature, pressure, and nutrient loading has shown that for the natural population of microorganisms seeded in this study, the nutrient loading exerted the most influence on population distributions. Large changes in the microbial population were documented. This phenomenon indicates that the mechanism of film development is, at least in part, due to changes in bacterial populations. Detailed understanding of the population changes is necessary to achieve a fundamental understanding of any biofouling process.