Columnar Denitrification Of A
Munitions Manufacturing Wastewater
DAVID O. TUCKER, Supervisor
Occoquan Watershed Monitoring Laboratory
Manassas, Virginia 22110
CLIFFORD W. RANDALL, Professor
PAUL H. KING, Professor
Virginia Polytechnic Institute & State University
Blacksburg, Virginia 24061
INTRODUCTION
The presence of nitrates in water supplies contributes to the enrichment of the nation's
lakes and estuaries (1,2,3) and can cause a disease in infants called methemoglobinemia (4).
For these reasons and as a part of the general interest in improving the environment, it has
become necessary to consider possible ways of preventing the release of nitrates into
streams and lakes.
Biological denitrification has been found to be an effective means of removing nitrates
from water (5,6). Although many studies have been made using this method, most have involved the removal of nitrates from secondary sewage effluents by modified activated
sludge systems. Little work has been done on the removal of nitrates from industrial effluents, and no references could be found on columnar denitrification of an industrial
waste. In addition, most work has involved the use of a synthetic carbon source, such as
methanol, with little emphasis on utilizing another waste high in carbon and low in nitrates
as a carbon source. However, among the wastes produced by munitions manufacturing are
one which is high in carbon and low in nitrates and one which is high in nitrates and low in
carbon. It would appear these wastes could be treated simultaneously. Wastes of these types
are discharged at the Radford Army Ammunition Plant, Radford, Virginia. The carbon
waste comes from the "Water Dry Process" (a solvent recovery process), and the nitrate
waste is produced during the manufacturing of nitroglycerin.
The investigation was designed to study the feasibility of treating the two industrial
wastes, one high in nitrates and low in organic matter, the other high in organic matter and
low in nitrates, in a denitrification unit. The experiments were also designed to provide information concerning rapid denitrification in a columnar unit. Therefore the wastes were
mixed to the desired proportions and subjected to columnar denitrification.
BACKGROUND AND REVIEW OF PREVIOUS STUDIES
Dissimilatory nitrogen removal or anaerobic denitrification is the use of nitrate as the
terminal electron acceptor in a biological system. Instead of tying up nitrogen in cell mass
(assimilative nitrogen removal) the microorganisms reduce nitrate from its positive five
valence state to elemental nitrogen with a valence state of zero. The elemental nitrogen is
then released to the atmosphere or carried from the treatment unit dissolved in the effluent.
The half reactions describing anaerobic denitrification are given below (7):
1/2 NO, + H+ + e- 1/2 H20 + 1/2 N02"
1/3 N02" + H+ + e" - 1/3 H20 + 1/6 N2 + 1/3 OH"
1/5 N03+ H+ + C-2/5 H20+ 1/10 N2+ 1/5 OH"
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