Algae Separation From Oxidation Pond Effluents
A.A. FRIEDMAN, Assistant Professor
Department of Civil Engineering
Tennessee Technological University
Cookeville, Tennessee 38501
DAVID A. PEAKS, Project Engineer
AWARE, Inc.
Nashville, Tennessee 37202
R.L. NICHOLS, President
Nichols Engineering Services, Inc.
Union City, Tennessee 38261
INTRODUCTION
During the preceding two decades, thousands of oxidation ponds or stabilization
lagoons have been built by municipalities and industries to meet secondary wastewater
treatment objectives (1). Low capital cost accompanied by minimal operation and
maintenance costs relative to conventional biological wastewater treatment systems led to
the rapid adoption by designers concerned with treating small flows or seasonal
wastewaters wherever land was relatively inexpensive. Design criteria based on organic
surface loading rates and hydraulic detention times have been developed and adopted by
most states.
In general, well designed and operated stabilization lagoons have proven effective in
removing soluble organic material from wastewaters. However, in recent years analyses of
maturation and facultative lagoon effluents have indicated that effluent algae carryover can
impose a significant oxygen demand on receiving waters (2, 3). Theoretical calculation of
the oxygen demand created by algae destruction suggests that 1.58 mg of 02 are required to
oxidize one mg of algae (dry weight) to C02 and water. Bare, et al. (4) found that 1.11 mg O,
was required per mg of algae obtained from laboratory studies and 0.81 mg 02 per mg algae
obtained from field studies. Varma and Digiano (5) reported that 0.67 mg 02 was required
for each mg of algae destroyed. Data resulting from algae obtained in both laboratory and
field experiments during this study indicate an oxygen demand of 1.19 mg 02 per mg algae
as shown in Figure 1.
Despite the cited differences in oxygen demand per unit weight of algae, one can
conclude that a significant oxygen demand is imposed on receiving waters by algae
discharged from lagoon effluents. Only the removal or destruction of algae prior to
discharge can sufficiently improve effluent quality to an acceptable level so that lagoons can
again be considered suitable for the design of low cost wastewater treatment systems. In
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