35    BIOLOGICAL NUTRIENT REMOVAL:
A PILOT PLANT STUDY
Syed R. Qasim, Professor
Department of Civil Engineering
The University of Texas at Arlington
Arlington, Texas 76019
Clinton E. Parker, Professor and Chairman
Department of Civil Engineering
The University of Texas at Arlington
Arlington, Texas 76019
Robert T. McMillon, Superintendent
Wastewater Treatment Plant
City of Fort Worth, Texas 76101
INTRODUCTION
In 1980 a research program was initiated using bench-scale laboratory reactors to study an anoxic/
anaerobic/aerobic treatment train for biological nutrient removal. In 1985 a pilot plant was constructed to field test the treatment process. These facilities were operated at varying flow and Qr/Q
ratios, and at effective mixed liquor suspended solids (MLSS) concentrations. The results of 25-
months of pilot-plant operational data indicated that the effluent concentrations of total BOD, TSS
and nitrate nitrogen were less than 10 mg/L. Ammonia nitrogen was less than 2 mg/L. The solids
settleability was excellent, and foaming due to Nocardia, was effectively controlled. Influent BOD
concentrations of less than 89 mg/L significantly reduced the system's ability to remove phosphorus.
A strong relationship between the amount of carbon source in the influent, phosphorus release in the
anoxic and anaerobic tanks and phosphorus uptake in the aeration basin was established.
BACKGROUND INVESTIGATIONS
Biological Nutrient Removal
The importance of nitrogen and phosphorus in stimulating eutrophic conditions has been well
documented and, as a result, over the last decade an increase emphasis has been placed on limiting
these elements in wastewater effluents. Separate treatment processes capable of removing either
nitrogen or phosphorus are well established. Both the theoretical and practical aspects on nitrogen
removal are well understood. However, theories that explain the mechanism(s) responsible for the
excess biological phosphorus uptake and the success of biological phosphorus removal has not been
agreed upon.
Conditions for the separate removal of nitrogen and phosphorus by a biological system are well
accepted. Anoxic conditions and a suitable carbon source are required for denitrification and the
release of gaseous nitrogen. Conditions for nitrogen removal are shown in Figure 1.
Phosphorus removal conditions are shown in Figure 2. Phosphorus uptake is a temporary excess
uptake by a biomass that has been stressed under anaerobic conditions. Timely separation of the
biomass from the liquid phase after exposure to aerobic conditions is essential. Arvin has provided a
good review of recent advances made in biological phosphorus removal.'
Bench scale results from a treatment train capable of significant nutrient removal and that can be
easily added to an existing activated sludge treatment plant have been previously reported.2"5 The
purpose of the work reported here was to evaluate the treatment train under field conditions, to
establish operational variables and environmental criteria for removal of phosphorus and/or nitrogen
and to evaluate how maximizing the removal of one influences the removal of the other.
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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