15    THE EFFECT OF PENTACHLOROPHENOL ON ENHANCED
BIOLOGICAL PHOSPHORUS REMOVAL IN SBR
SYSTEMS
Larry Benefield, Professor
Sung Kim, Graduate Student
Department of Civil Engineering
Auburn University, Alabama 36849
Clifford Randall, Professor
Department of Civil Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061
INTRODUCTION
Municipal wastewater effluents containing phosphorus accelerate eutrophication in receiving
waters in which phosphorus is the limiting nutrient. For this reason, wastewater effluent phosphorus
control is important in many regions. Although chemical precipitation is a proven technology capable
of meeting phosphorus discharge restrictions, the production of considerable quantities of chemical
sludge has created disposal problems. Disposal processes such as incineration and land application are
limited in their ability to handle chemical sludges. Biological phosphorus removal would seem to
provide a more cost-effective and environmentally sound means of removing phosphorus from wastewater effluents because it eliminates or greatly reduces sludge disposal problems.
Actually, the need to meet existing phosphorus effluent limitations is not required to justify the
installation of phosphorus removal systems. From an operational point of view, a suspended growth
nutrient removal system, in which denitrification and biological phosphorus removal are accomplished, is less energy intensive than the commonly used totally aerobic suspended growth system
which provides only carbon oxidation and nitrification. The reason for this is that it is theoretically
possible to recover 62.5% of the oxygen required for nitrification if the nitrates produced are recycled
and used as electron acceptors for oxidation of organic matter in the influent wastewater. For a
typical municipal wastewater, this could result in a total energy savings of 15 to 20%, depending on
the extent of denitrification. Also, the presence of the anaerobic zone required for enhanced phosphorus removal would also provide the opportunity for a certain amount of the organic material to be
stabilized under anaerobic conditions. This would further reduce the oxygen requirement for organic
stabilization. In a biological phosphorus removal study conducted by Randall, Brannan and Benefield,1 anaerobic stabilization was found to be very significant with respect to the total organic
stabilization that occurred within the system. It was 30% of the total stabilization at a 20-day sludge
age and 23% at a 12-day sludge age, using a synthetic wastewater. This represents potential aeration
energy savings that can be realized by using biological phosphorus removal. Thus, when operated
properly, biological nutrient removal systems that accomplish carbon oxidation, nitrification, denitrification and phosphorus removal will provide significant energy savings when compared with a
biological system where only carbon oxidation and nitrification are accomplished. The benefits of
such a treatment system are obvious-better treatment for less energy.
To date, most of the operational data for enhanced biological phosphorus removal systems have
been obtained from lab scale units fed easily degradable organic substrates or full scale systems
treating primarily domestic wastewaters. Little information is available regarding the effects of potentially inhibitory materials on the enhanced biological phosphorus removal process.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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