Mass Culturing of Algae in Controlled
Light-Dark Detention Systems:
I. Effects of Culture Density
GORDON R. PYPER, Associate Professor
Department of Civil Engineering
Norwich University
Northfield, Vermont
WALTER J. WEBER, JR., Associate Professor
JACK A. BORCHARDT, Professor
Department of Civil Engineering
University of Michigan
Ann Arbor, Michigan
INTRODUCTION
The pollution-accelerated aging of surface waters has become a matter of
widespread concern over the past several years (1,2): indeed, eutrophication is a
popular focal point in any discussion of our national water pollution problems.
Continuing increases in daily volumes of wastewater discharged to lakes, rivers,
and other receiving waters are to be expected in the face of a continuously expanding population. It would appear, therefore, that the only feasible measure
for protection of the quality of our natural waters --at least as far as controllable
discharges are concerned -- lies in more thorough purification of wastes prior to
release.
Conventional treatment of wastewater has been directed for the most part to
reduction of BOD, the magnitude of such reduction generally being considered
satisfactory if the DO concentration of the receiving water into which the waste is
discharged is not decreased to a level below four mg/1 at any point on the oxygen
sag curve, and provided no gross esthetic changes are produced. Little concern
has been given to concentrations of biological nutrients, many of which are byproducts ofthe treatment process, which tend to fertilize receiving waters and thus
accelerate eutrophication. Of these nutrients — which include nitrogen, phosphorous, hormones, vitamins, and other essential trace elements (3) -- nitrogen
and phosphorous are of most general concern because they are usually present in
greatest quantity and because they are so important for aquatic plant growth. The
common ranges of concentration of nitrogen and phosphorous in waste effluents are
seven to 15 mg/1 and two to four mg/1, respectively.
Some observations have indicated that concentrations of 0.01 mg/1 of inorganic phosphorous and 0.30 mg/1 of inorganic nitrogen are sufficient to support
algal blooms (4). Therefore, nutrient levels in waste effluents are often sufficient
for complete fertilization of otherwise infertile receiving waters. The engineer
concerned with water pollution and protection of our national water resources
must be concerned with the undesirable effects of nutrients on receiving waters.
It is apparent that measures to alleviate undue fertilization of natural waters must
include removal of these nutrients from waste discharges.
Both biological (5) and chemical (6) methods have been considered for ex-
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