The Relationship of Algal Exocellular
Polymers to Biological Flocculation
JOSEPH L. PAVONI, Assistant Professor
Department of Civil and Environmental Engineering
Speed Scientific School
University of Louisville
Louisville, Kentucky
MARK W. TENNEY, Associate Professor
WAYNE F. ECHELBERGER, Jr., Associate Professor
Department of Civil Engineering
University of Notre Dame
Notre Dame, Indiana
INTRODUCTION
In the simplest sense, all microscopic plants carrying out true photosynthesis
may be defined as algae. In actuality the term includes a number of types of
organisms which differ profoundly from one another in cell organization,
consequently, they have little in common except that their characteristic mode of
nutrition is photosynthetic and they cannot be included in any other division of the
plant kingdom. Algae utilize inorganic compounds to develop protoplasmic material
and are therefore classified as autotrophic organisms.
Recently, much attention has focused around algae in environmental systems.
The increasing appearance of algal blooms on surface waters has accelerated interest
in nutrient removal schemes applicable to effluents from existing wastewater
treatment plants. Some of these third stage, or tertiary, treatment processes have
utilized algae to "strip" the basic nutrients from solution by means of normal algal
metabolism. Also since algae represent a concentrated mass of proteins, fats, and
carbohydrates, there has been interest in experimenting with methods of collecting
excess algae in ponds for possible commercial food usages. In general then, algae
represent a highly concentrated, relatively pure mass of usable organic material that
can be produced continuously, quickly, and cheaply while serving at the same time as
a means of processing unwanted community wastes.
One of the serious drawbacks in any of the above systems involving algae is the
separation of these microorganisms from the corresponding liquid phase. Regardless
if one is considering nuisance conditions in surface waters, or nutrient "stripping"
processes, or commercial production of algae for food supplies, feasible methods of
harvesting algae in all cases becomes of utmost importance. Among the various
separation methods that have been investigated are: centrifugation, chemical
treatment, filtration, floatation, ion-exchange, sedimentation, straining, and
bioflocculation. Most methods are quite costly, however, properly managed
bioflocculation techniques may offer a feasible, as well as, economic solution to
algal-liquid separation.
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