SIMPLIFIED NOD DETERMINATION
Joseph L. Slayton, Chemist
E. Ramona Trovato, Chemist
U.S. Environmental Protection Agency
Region III, Annapolis Field Office
Annapolis, Maryland 21401
INTRODUCTION
Biochemical oxygen demand (BOD) is a bioassay procedure concerned with the utilization of oxygen in the biochemical oxidation (respiration) of organic material. This test
is one of the most widely used measures of organic pollution and is applied both to surface and wastewaters. The standard method of BOD measurements adopted by APHA [ 1 ]
is a five-day test in which a water sample is maintained at 20 C in the dark and oxygen
depletion is monitored. The five-day incubation period was selected to maximize the
oxygen demand associated with the oxidation of carbon compounds while minimizing the
oxygen demand of autotrophic organisms. That portion of the BOD due to the respiration of organic matter by heterotrophic organisms is termed the carbonaceous oxygen
demand (CBOD) and that portion involved with nitrification is termed nitrogenous oxygen
demand (NOD). The desire to separate NOD and CBOD results not only from the fact
that the organisms responsible for these components have different nutrient requirements,
but also because they differ in reaction rates A02/Atime, temperature coefficients and
tolerance to toxic materials. Nitrifying bacteria are in general slower growing [2], more
drasticaUy affected by temperature [3], and are more sensitive to materials like [4]
phenols, cresol, halogenated solvents, heavy metals and cyanide. The organisms involved
in the CBOD and NOD processes would therefore be expected to react differently to the
same aquatic environment. The determination of the BOD components would better
define the BOD test results and aid in extrapolating these results to the prediction of
dissolved oxygen profiles in a body of water.
The purpose of this paper is to demonstrate that a simple procedure involving an
inhibitor to nitrification, N-serve, could provide an accurate and precise measurement of
nitrification occurring in the BOD test whde not affecting the carbonaceous oxygen
demand.
NITRIFICATION
Nitrification is the conversion of ammonia to nitrate by biological respiration. This
type of respiration is employed by seven genera of autotrophic nitrifyers [5].
It should be noted that heterotrophic nitrification can also produce N02" and N03"
by reactions that do not involve oxidation [6]. However, only Nitrosomonas spp. and
Nitrobacter spp. are regularly reported by in situ nitrification studies [2]. Therefore, the
treatment of nitrifying river samples with inhibitors specific to Nitrosomonas and Nitrobacter can be expected to stop all appreciable nitrification [7].
The reactions involved in nitrification are as follows:
NH4+ + 1.5 02   NitrOSOm°na.S  2H+ ♦ NO," ♦ H20 (1)
Nitrobacter
N02  + 0.5 02    +- N03 (2)
The stoichiometrics of the nitrification reactions dictate that the conversion of 1 gram of
nitrogen from ammonium to nitrite utilizes 3.43 grams of oxygen, and the conversion of
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