Biological Denitrification of High Nitrate
Waste Solutions
F.E. CLARK, Development Chemist
H.C. FRANCKE, Development Supervisor
J.W. STROHECKER, Development Consultant
Union Carbide Corporation
Nuclear Division
Oak Ridge, Tennessee 37830
INTRODUCTION
Most of the nitric acid used in the purification of uranium at the Oak Ridge Y-12 Plant
of the U.S. Energy Research and Development Administration is finally evolved as a dilute
acid process waste or as a waste solution of nitrate salts. These solutions are products of the
liquid-liquid solvent extraction procedures used in the purification process where the acid is
a principal reagent.
In previous years these nitrate-rich solutions, laden with impurities removed from the
uranium in the liquid-liquid extraction process, have been pumped into four ponds at the
west end of the plant. Each pond is about one acre square and approximately 20 feet deep.
The ponds were constructed in such a manner that only direct fall precipitation could enter
the ponds. No known overflow over or around the pond banks has occurred. Evaporation
and percolation into the soil has occurred at a satisfactory rate to keep the pond levels
reasonably constant and below the overflow point. This pond system of waste liquid
disposal was constructed about 20 years ago because even then it was recognized that this
large a quantity of nitrate could have a disastrous effect upon environment if released into
ground-water streams. At the time of pond construction a limit of 20 mg/ dm3 total nitrogen
was established as the maximum permissible limit at a sampling station in a nearby creek
about 4'/? miles west of the Y-12 Plant. This 20 mg/dm3 nitrogen is equal to about 89
mg/dm3 as nitrate. This level of nitrogen in the creek waters has not been exceeded, based
c n analyses of composite samples taken at the sampling point. The ponds satisfied the
i ;quirements regarding pollution up to the present. However, changes in state and federal
water pollution control laws and the institution of the National Pollutant Discharge
Elimination System (NPDES) suggest that pumping of nitrate waste solution into the
ponds should be discontinued to improve the water quality in the nearby creek.
Consideration of other methods of disposal of these high nitrate liquid waste materials
was undertaken in the latter part of 1972. Methods of disposal considered were: 1)
Neutralization with lime and calcination; 2) Neutralization with lime and conversion to
liquid fertilizer; 3) Neutralization with lime and conversion to solid fertilizer; 4)
Neutralization with lime followed by burial; 5) Neutralization with lime followed by
biodenit rification; and 6) Recovery and recycling usable chemicals and biodenitrification of
the remainder.
768