REMOVAL OF FLUORIDE AND PHOSPHORUS FROM
PHOSPHORIC ACID WASTES WITH TWO-STAGE LIME TREATMENT
Gregory A. Mooney, Manager
Cliff G. Thompson, Regional Manager
Black, Crow and Eidsness, Inc.
A Division of CH2M Hill
Montgomery, Alabama 36104
Alfred T. Nogueira. Engineer
Agrico Chemical Company
Donaldsonville, Louisiana 70346
INTRODUCTION
Production of phosphoric acid in the fertilizer industry generates considerable quantities of acidic cooling water with high concentrations of phosphorus and fluoride [ 1 ].
These problems are particularly acute in areas where a large amount of the annual rainfall occurs over a relatively short portion of the year, resulting in required storage of
runoff from large land areas used for waste gypsum stacking and evaporative cooling
ponds.
Even though many production facilities are in a negative water balance on an annual
average basis, these periodic hydrologic imbalances frequently exceed available storage
and discharge of cooling pond water is necessary.
Increasing pond depths can reduce the magnitude of the problem, but this is
extremely expensive for existing facilities.   Use of cooling towers to replace evaporative
cooling does not eliminate treatment requirements since blowdown from the tower
system is necessary.
This paper discusses the development and design of a liming system to treat waste
flows that result after every effort is made to manage pond systems and to reuse cooling
water in production processes.
Regulatory Requirements
Established EPA effluent guidelines require that there be no discharge of process
cooling water.    Exceptions are made for discharge with treatment to established limits
when pond discharge is necessary.   EPA requires maintenance of pond surge capacity
equal to the runoff from a 10-year 24-hour rainfall event for BPT, and a 25-year
24-hour rainfall event for BAT and new sources.   Treatment may begin when the pond
level rises into the surge capacity, and must begin at the mid-point of the surge capacity.
Effluent limitations are concentration-based with average limits of 25 mg/1 and 35
mg/1 for fluoride and phosphorus respectively.      An additional limit of 9 picocuries/liter
of radium-226 radiation was established [2].
Need for Studies
In the Guidelines Document which proceeded these standards, double lime treatment
was established as the available technology for BPT, BAT, and new sources with little
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