Production of
Large Concentrations of a
Filamentous Alga on Organic Wastes
WESLEY O. PIPES, JR., Assistant Professor of Civil Engineering
Northwestern Technological Institute
Evanston, Illinois
One of the features which distinguishes high rate from conventional
stabilization ponds is the fact that the concentrations of algae attained in the
high rate ponds is much greater than those produced in conventional ponds.
Concentrations of algal solids as great as 300 mg/l have been attained in
pilot plant high rate ponds, and concentrations in the range 150-250 mg/l are
frequently observed (1). These relatively great algal solids concentrations are
necessary for the proper operation of high rate stabilization ponds because
photosynthesis is relied upon as the primary means of oxygen supply.
If the effluent from a high rate stabilization pond should reach a body
of water in which the environmental conditions were adverse and the algae
were killed,   the organic load released from the dead algal cells would be
freater than the organic load of the original waste. For this reason it has been
elieved that it would be necessary to remove the algae from the effluent
from a high rate stabilization pond. Also, if the algae produced in a high
rate stabilization pond could be harvested, dried, and packaged at a reasonable cost, they could be sold as animal feed.
An extensive study of the possible methods of harvesting algae from
high rate stabilization ponds was previously carried out at the University of
California (2). This study covered such methods of harvesting as centrifuga-
tion, flocculation and sedimentation, filtration, screening, electro-static
precipitation, and removal on ion exchange resins. The results of this study
indicated that not only the initial harvesting but also dewatering and drying
of the algal solid would be expensive.
Normally unicellular green algae such as Chlorella and Scenedesmus are
the predominant algal organisms in stabilization ponds. Because of their
small size these algae settle very slowly and retain large amounts of bound
water. It is evident that if a high rate stabilization pond could be operated
so that the predominant algal species was a filamentous organism which could
be harvested by sedimentation or microstraining, the cost of recovering the
algae might be reduced considerably.
A preliminary search for filamentous algae which could grow in grossly
polluted water resulted in the isolation of a species of Oscillatoria which
grew well in domestic sewage and in a synthetic milk waste. A series of laboratory experiments indicated thatwhen this organism was grown inlaboratory
cultures on sewage or a synthetic dairy waste, the rates of algal production
and BOD removal were comparable to those attained with Chlorella or
Scenedesmus (3). It Was also shown that the Oscillatoria filaments could
easily be separated from the waste by sedimentation.
Once it was shown that this organism is able to grow well in organic
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