AWWA WQTC64164

Algae species differ in terms of their cell morphology and extracellular organic matter (EOM) excretion patterns. Biologists traditionally classify algae according to their evolution and pigmentation, which may be appropriate for biological purposes but is not informative from a water treatment perspective. A more functional descriptor may be a species' morphology which is considered to have a significant affect on coagulant demand, although algal EOM is also considered to significantly affect coagulation. The current paper characterizes three common species found in water treatment reservoirs - Chlorella vulgaris (green algae), Microcystis aeruginosa (blue-green algae) and Asterionella formosa (diatom) in terms of both their cell morphology and EOM concentration and composition. The charge density, cell surface area and the zeta potential of the suspension is analyzed. The EOM of each species is analyzed for: dissolved organic carbon (DOC); charge density; and, degree of hydrophobicity using XAD resins. The relative contributions of cell morphology and EOM excretion to coagulant demand for successful removal are investigated. Specifically, the research has demonstrates that, despite having similar visual attributes, e.g. size and shape, C. vulgaris and M. aeruginosa have very different coagulant demands. A. formosa was found to have a larger coagulant demand relative to its charge density which was accounted for by its complex cell morphology. It is observed that a correlation exists between increasing complexity of cell structure and coagulant demand. There is therefore a case for re-categorizing algae based on this correlation such that it is straightforward to identify a typical coagulant dose for treating a particular algae bloom. EOM concentration and composition will affect this relationship to an extent. Furthermore, the coagulation process can be monitored by zeta potential to ensure that the coagulant is reducing the zeta potential to the extent necessary for good removal. Includes 16 references, tables, figures.