PHOSPHORUS REMOVAL IN A PILOT-SCALE TRICKLING FILTER
SYSTEM BY LOW-LEVEL LIME ADDITION TO RAW WASTEWATER
Roy D. Miller, Research Sanitary Engineer
Robert S. Ryczak, Research Sanitary Engineer
U. S. Army Medical Bioengineering Research
and Development Laboratory
Fort Detrick, Maryland 21701
A. Ostrofsky, Environmental Engineer
U.S. Army Construction Engineering Research Laboratory
Champaign, Illinois 61820
INTRODUCTION
Phosphorus removal studies were undertaken to provide advanced wastewater treatment
technology for application at U.S. Army wastewater treatment plants.   Department of the
Army secondary treatment plants consist primarily of trickling filters.   Plant sizes range
between 0.1 to 5.0 million gallons per day (mgd).   Army installations, like municipalities
and industry, are issued National Pollutant Discharge Elimination System (NPDES) permits with effluent discharge standards [ 1 ].   Since the NPDES permits do not specify actual treatment processes, the Army may use one of three alternatives for permit compliance.   The installation can tie into a regional or areawide system, use land application or
provide advanced wastewater treatment.
Approximately 35% of the 150  major Army installations and activities in the United
States are connected or are pending connection to areawide systems.   Sixty percent of the
remaining installations will require only secondary treatment to meet 1 July 1977 standards.   The rest require the application of some form of advanced waste treatment technology to meet effluent limitations with 40% requiring phosphorus removal.   The actual
number of treatment facilities involved is higher since some installations have more than
one plant.   Phosphorus effluent limitations in these facilities will range from 0.2 to 2.0
mg/1 with a modal value of 1.0 mg/1 (as P) after 1 July 1977.
Requirements for design criteria included system effectiveness for phosphorus removal
and the use of existing equipment and facilities in upgrading efforts rather than new construction.   Simplicity of operation and maintenance, minimum laboratory requirements
and potential wide application to Army trickling filter systems were also identified as requirements.   Compatability with other treatment processes (e.g., nitrification and solids
disposal), enhanced biochemical oxygen demand (BOD), suspended solids, fecal coliform
and heavy metal reduction were listed as highly desirable.
Technology assessment began with a literature review of the state-of-the-art of phosphorus removal technology and included a review of existing NPDES permits and treatment facility characteristics.   Chemical treatment was identified as the technology of choice.
Commonly used chemicals for phosphorus removal include lime and salts of aluminum and
iron.   These chemicals have been applied at various addition points in biological treatment
systems.   Lime is usually associated with high pH levels and recarbonation requirements
and has not been previously recommended for use in trickling filter systems except as a
tertiary process [2].
Comparisons of the chemicals involved indicated that lime dose could be simply controlled by control of pH while salts of aluminum and iron required that dosing be based
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