Biological Nitrification with the High Purity
Oxygenation Process
MICHAEL J. STANKEWICH, JR.,
Linde Division, Union Carbide Corporation
Tonawanda, New York
INTRODUCTION
The removal of nitrogenous oxygen demand and, in some cases, complete nitrogen
removal from wastewater is receiving increased attention in water pollution control. There
are several reasons which make it desirable to remove ammonia from wastewater. These include the facts that ammonia exerts a considerable oxygen demand on the receiving water,
that it is toxic to fish and that it exerts an extra chlorine demand and reduces disinfection
effectiveness. It is generally agreed upon that, at this time biological nitrification is, from
the technical and economic viewpoint, the most feasible method of removing ammonia
from wastewater.
Biological nitrification is performed by two general groups of aerobic autotrophic
bacteria; Nitrosomonas and Nitrobacter, which respectively oxidize ammonia-nitrogen
(NH3-N) to nitrite-nitrogen (NOj-N) and nitrite-nitrogen to nitrate-nitrogen (NO3-N) as
their energy sources. These organisms require an oxygen enriched environment and in
addition, as autotrophs, require inorganic carbon in the form of carbon dioxide or bicarbonate as their carbon source.
Biological nitrification is an integral part of the natural nitrogen cycle. The principal
species and conversion pathways of nitrogen in natural water and sewage environments are
shown in Figure 1. Organic nitrogen and ammonia are the common species found in raw
wastewaters and are jointly measured as total Kjeldahl nitrogen. In a biological suspended
growth process organic nitrogen is converted to dissolved ammonia through the process of
deamination during bacterial metabolism of organic materials. During bacterial synthesis,
ammonia is converted to cellular organic nitrogen through assimilation. As bacteria and
other microorganisms die during the process they lyse producing residual organic nitrogen.
A fraction of the TKN is removed during the carbonaceous removal step through bacterial
syntheses and correspondent wasting of excess sludge.
If proper conditions are provided for the growth and maintenance of nitrifying
organisms, nitrification will proceed. If the nitrified waste is then subjected to an anaerobic
heterotrophic bacterial population denitrification will proceed. In this case, nitrate and nitrite are subsequently reduced resulting normally in free nitrogen (N2). These denitrifying
bacteria require an organic carbon source for synthesis.
Increasing interest in nitrogen removal processes and the potential advantages of the
high purity oxygenation system for biological aeration processes prompted Union Carbide
to explore nitrification as a part of its overall technology program related to high purity oxygenation. These efforts, among others, include two laboratory development pilot plant
studies on both single-step and second-step nitrification conducted at Union Carbide's
Tonawanda, New York facilities and a two-step carbonaceous removal and nitrification
pilot plant program conducted with municipal wastewater at a Northeastern location.
These experiences, as well as the basic biokinetic model and design consideration utilized in
nitrification designs, are discussed herein.
TYPES OF BIOLOGICAL NITRIFICATION PROCESSES
There are two general process schemes which can be used to obtain nitrified effluents as
shown in Figure 2. The first is a single step process in which both carbonaceous removal
and nitrification occur in the same reactor. From the discussion of population dynamics it
1