AWWA MTC69695

The objective of this powerpoint presentation was to study membrane fouling by algae. An algal bloom was created in the laboratory, and fluorescence microscopy was used to evaluate and count phytoplankton cells. The effects of shear on cells was studied by passing cells through a valve orifice at high pressure, and monitored the cell breakup with flow cytometry. Cell number decreased over time while small-particle concentration increased. Fluorescence and absorbance increased with shear. The results were similar with 100-kDa ultrafiltration. Hermia's models (1982) were used to evaluate differences in fouling mechanisms. The best data fit was obtained for each model in each membrane filtration experiment. Models moved from complete blocking toward cake filtration before and after shear, respectively, and rejection of carbohydrates decreased after shear. Conclusions indicate that: algal populations have a distribution of cell structural strength; the strength distribution determines breakup under shear; an increased understanding was gained of how Hermia's models apply to filtration of natural systems; shear is detrimental to pretreatment membrane productivity; and, shear decreases rejection of organic matter, which is detrimental to downstream RO membranes. Includes table, figures.