52   TOXICITY RESPONSE OF BIOLOGICAL PHOSPHORUS
REMOVING ACTIVATED SLUDGE
D.H. Zitomer, Research Assistant
R.E. Speece, Centennial Professor
Environmental and Water Resources Engineering
Vanderbilt University
Nashville, Tennessee 37235
INTRODUCTION
Ordinarily, low phosphorus concentrations, in natural waters prevent overgrowth of algae and
foster a balanced ecosystem. When wastewater effluents containing phosphorus are released to natural waters, algal growth can be stimulated and other deleterious eutrophic conditions may predominate. In an effort to prevent this, environmental policies have emphasized the reduction of phosphorus loads to sensitive receiving waters. For example, the Chesapeake Bay Agreement (1987) and
the Great Lakes Water Quality Agreement (1978) require that effluent phosphorus concentrations be
greatly reduced.1 As a result, some National Pollution Discharge Elimination System (NPDES)
permits require monthly average effluent phosphorus concentrations less than 1-mg/L.
To meet these stringent requirements, aluminum or iron salts are often added to wastewater.
Subsequently, the metal-phosphate precipitates which form are removed by clarification. Disposal of
the resulting sludge is often costly. Enhanced biological phosphorus (bio-P) removal has also been
employed to meet effluent requirements. In this system, removal is accomplished by bio-P bacteria
which store phosphorus in great quantities. Therefore, phosphorus can be removed in the form of bio-
P waste sludge which is approximately 10% by (dry) weight phosphorus,2 in contrast to typical waste
activated sludge which is approximately 2% phosphorus. Since metal salt addition often becomes
unnecessary, large quantities of precipitate sludge are not produced.
The biochemical reactions of bio-P removal have been studied and a fundamental understanding of
the process is emerging.3"9 An anaerobic environment high in substrate followed by an aerobic
environment low in substrate is essential. Anaerobically, phosphate is released, providing energy for
substrate uptake and storage in the form of poly-/3-hydroxybutyrate (PHB). Subsequently, PHB is
oxidized in the aerobic environment and phosphate is biologically removed to provide energy for the
next anaerobic feed period. Perhaps the most characteristic feature of bio-P systems is the sequence of
anaerobic and aerobic environments required for selection of a biological culture high in phosphorus
content.
If bio-P systems are to be optimized to reduce effluent phosphorus concentrations, an understanding of the toxicity response of enhanced phosphate removing cultures must be developed. Although
little information regarding toxicity response of bio-P bacteria exists, a few researchers have studied
the phenomenon.
This paper focuses on the effect of acetone, phenol, 4-chlorophenol and 2,3-dichlorophenol on
anaerobic phosphorus release and aerobic phosphorus uptake in bio-P systems. Acetone was studied
because it is often used as a solvent for other toxicant stock solutions and its effect at high concentration is of significance to future research. Phenol, 4-chlorophenol, and 2,3-dichlorophenol were
selected because they represent relatively soluble, nonvolatile priority pollutants which could be
present in wastewaters treated at publicly owned treatment works.
PREVIOUS INVESTIGATIONS
The impact of cyanide, copper, and phenol on bio-P systems was investigated.10 Toxicant spikes at
the concentrations studied did not affect phosphorus release during an initial 2-hour anaerobic
period, but did affect 4-hour aerobic uptake. For example, cyanide concentrations of 3-mg/L and
5-mg/L resulted in loss of enhanced phosphorus uptake, while 1-mg/L cyanide had little effect on the
process. Copper, in particular, was found to markedly inhibit phosphorus uptake. At copper concen-
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
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