IMPROVED PERFORMANCE IN COMBINED
NITRIFICATION/DENITRIFICATION
Curtis C. Panzer, Chemical Engineer
Michael Komanowsky, Chemical Engineer
Gerard E. Senske, Chemical Engineer
Eastern Regional Research Center
U.S. Department of Agriculture
Philadelphia, Pennsylvania 19118
INTRODUCTION
By July 1984 industrial point sources in the United States wdl be required to meet
effluent Umitations consistent with the EPA's standards of "best avadable (treatment)
technology economicady achievable" (BAT). For the cattlehide tanning industry, substantial modification in both processing and effluent treatment practices wdl likely be
required in order to meet BAT limitations [1]. Significantly, no treatment facdity to date
has demonstrated the capabdity of meeting the proposed requirements. A Carrousel biological treatment system, in use at the A.C. Lawrence Shearling Tannery in Winchester, NH,
however, appears to hold great promise [2]. The Carrousel system at this facility is a single
sludge treatment system operated to provide both nitrification and denitrification. Such
systems wdl be hereafter described as combined nitrification/denitrification or combined
N/D systems.
At the Eastern Regional Research Center, U.S. Department of Agriculture, a combined
N/D system is being evaluated. On the basis of studies conducted, we bedeve that proposed
limitations for both COD and TKN can be met. In addition, results show that the slow rate
of denitrification normady associated with combined N/D systems can be improved by use
of staged denitrification [3]. The purpose of this chapter is to describe results that demonstrate these findings.
THEORY
Extent of Nitrogen Removal
A combined N/D treatment system is shown in Figure 1. Apart from the internal staging,
this system is the same configuration as that first suggested by Ludzack and Ettinger [4]
and the same as that comprising the first two stages of the Bardenpho process [5,6]. In
this system, the waste is nitrified in the aerobic zone and then is returned to the anoxic
zone to be denitrified. The higher the rate at which the aerobic mixed liquor is returned
to the anoxic zone, the greater the amount of nitrate that can be removed.
F, COD,., TKN„        J F, N«,   COO,.!   IKN„
IT
Figure  1. Schematic diagram for combined nitrification/denitrification.
From this flow scheme, a mass balance equation can be developed relating the nitrate
nitrogen in the effluent to the TKN of the influent and the ratio of the mixed Uquor recycle
rate to the feed rate [7j. The nomenclature used is defined as foUows:
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