Chemical Precipitation of Phosphate withi
a High Rate Bio-oxidation System
I. Synthetic Sewage Studies
W. A. EBERHARDT, FWPCA Research Fellow
J. B. NESBITT, Professor
Civil Engineering Department
Pennsylvania State University
University Park, Pennsylvania
INTRODUCTION
Be it in research, education, or regulatory policy formation, few areas of
water quality management receive the attention presently given the problems and
causes of surface water enrichment. Nevertheless, while descriptive examples of
eutrophication have been abundantly reported, the associated direct causes have
seldom been unequivocally defined. Commonly mentioned in this respect have
been increased levels of inorganic nutrients and/or growth factors. Of the former,
foremost attention has been directed toward phosphorus.
In order of usual importance, phosphorus gains access to surface waters via
wastewater (industrial and domestic), runoff, and groundwater. It has been considered likely that in some instances the removal of this nutrient from waste discharges will result in stream concentrations sufficiently low to limit vegetative
productivity in accord with Liebig's Law of the Minimum. Accordingly, phosphorus removal methods have been widely investigated.
With few exceptions, the processes considered have been tertiary in nature - -
a condition conducive to high costs. Recently, Nesbitt (1) reviewed the many
proposed schemes and evaluated each on the basis of effluent residual (assuming
a stream to waste dilution factor of 9:1, an effluent residual of 0.1 mg P/l or less
was considered desirable.) and annual costs. His analyses indicated promise for a
non-tertiary scheme utilizing chemical precipitation in conjunction with chemically aided bioflocculation in a short-term activated sludge process.
The concept of using iron and aluminum salts simultaneously for cell floc-
culation and phosphorus elimination was suggested by Stumm (2) ana later successfully tried on a batch basis by Tenney and Stumm (3). Realizing that biological
treatment occurs in two phases, substrate utilization and bioflocculation, they
reasoned that by chemically aiding flocculation the initial phase could be accomplished in a "high-rate, low-solids retention unit." The increased treatment
costs for phosphorus removal and flocculation would then be partially compensated
for by savings from the shortened biological phase. Work apparently of this nature
has also been conducted in Switzerland (4).
OBJECT AND PROCESS CONSIDERATIONS OF THIS INVESTIGATION
It was the object of this research to develop and study the effectiveness of a
continuously operated bench scale process combining chemical treatment and
activated sludge so as to effect low phosphorus residuals without any sacrifice in
biological treatment efficiency.
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