AWWA WQTC64164

Algae species differ in terms of their cell morphology and extracellular organic matter(EOM) excretion patterns. Biologists traditionally classify algae according to theirevolution and pigmentation, which may be appropriate for biological purposes but isnot informative from a water treatment perspective. A more functional descriptor maybe a species' morphology which is considered to have a significant affect oncoagulant demand, although algal EOM is also considered to significantly affectcoagulation.The current paper characterizes three common species found in water treatmentreservoirs - Chlorella vulgaris (green algae), Microcystis aeruginosa (blue-greenalgae) and Asterionella formosa (diatom) in terms of both their cell morphology andEOM concentration and composition. The charge density, cell surface area and thezeta potential of the suspension is analyzed. The EOM of each species is analyzed for:dissolved organic carbon (DOC); charge density; and, degree ofhydrophobicity using XAD resins. The relative contributions of cell morphology andEOM excretion to coagulant demand for successful removal are investigated.Specifically, the research has demonstrates that, despite having similar visualattributes, e.g. size and shape, C. vulgaris and M. aeruginosa have very differentcoagulant demands. A. formosa was found to have a larger coagulant demand relativeto its charge density which was accounted for by its complex cell morphology. It isobserved that a correlation exists between increasing complexity of cell structure andcoagulant demand. There is therefore a case for re-categorizing algae based on thiscorrelation such that it is straightforward to identify a typical coagulant dose fortreating a particular algae bloom. EOM concentration and composition will affect thisrelationship to an extent. Furthermore, the coagulation process can be monitored byzeta potential to ensure that the coagulant is reducing the zeta potential to the extentnecessary for good removal. Includes 16 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

12

File Size:

1 file , 400 KB