INFLUENCE OF UN-IONIZED AMMONIA AND INORGANIC CARBON
ON BIOLOGICAL NITRIFICATION
Albert J. Hill, Graduate Student
Ronald D. Neufeld, Associate Professor
Civil Engineering Department
University of Pittsburgh
Pittsburgh, Pennsylvania 15261
INTRODUCTION
The overall objective of this research is to conduct basic studies into possible causes of
biological nitrification process instability as currently observed in steel industry wastewaters,
and in the longer term to propose rational and pragmatic process and/or operational alternatives for the biological oxidation of ammonia.
The approach taken in this research is to quantify the influences of key reproducable
parameters on the biokinetics of nitrification. The parameters considered are alkalinity and
free (or un-ionized) ammonia.
Coking is the heating of bituminous coal in the absence of air; gases are given off and a
residue remains in the oven. The residue is coke, a major ingredient in the blast furnace manufacturing of pig iron. In a by-products coking operation the gases are captured for further
processing. This processing produces excess wastewater known as weak ammonia liquor.
The wastewater treatment scheme for coke plants consists of an ammonia stripping operation for free ammonia, dephenolization, pH adjustment, a fixed ammonia still, and final settling.
BPCTA added biological treatment to this scheme requiring that total ammonia discharge
levels not exceed 125 mg/1. BATEA is expected to change this standard to about 10 mg/1.
Some coke and blast furnace facilities have demonstrated capabilities to meet the 10 mg/1
ammonia discharge limit some of the time, few if any can meet such standards all of the time.
The need for a better understanding of available ammonia removal technologies, and for a
pragmatic and reliable treatment scheme, becomes critical [ 1 ].
The principal alternatives for the removal of wastewater ammonia are the physical-chemical
approaches of chlorination, ozonation, ion exchange, membrane processes, ammonia stripping
and biological nitrification. It is not the intent of this paper to examine the details of physical-
chemical techniques since they are presented elsewhere [2,3], however, a concise review of
biological nitrification is in order.
BIOLOGICAL NITRIFICATION
Of the processes available for the removal of ammonia from steel industry wastewater,
biological systems are the most pragmatic. They do not suffer from fouling as do ion-
exchange and membrane systems, nor do they suffer the icing and pH adjustment requirements of ammonia stripping. Data from steel industry operations indicate that a properly
designed and operated biological nitrification facility is capable of producing ammonia levels
of less than 10 mg/1 over extended periods of time. Biological nitrification processes,
however, are known to exhibit unaccounted for upsets and thus are considered unreliable.
pH has been reported to be a parameter of chief concern to biological nitrification
process instability. It is the opinion of these authors, however, that un-ionized ammonia is a
more fundamental parameter; un-ionized ammonia level being a function of wastewater total
ammonia and pH. Accordingly, it is appropriate to briefly develop the theory of biological
nitrification kinetics, and some of the current theory for the quantification of the influence
of toxic biokinetics of nitrification.
Although several genera of autotrophic bacteria have been identified as capable of causing
nitrification, the genera nitrosomonas and nitrobacter are considered responsible for most
naturally occurring nitrification as follows [4,5]:
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