TOWER-BIOLOGY® AND ITS APPLICATION
FOR THE NITRIFICATION/DENITRIFICATION
OF AMMONIA-RICH WASTEWATER
G. Diesterweg, Application Manager
I. Pascik, Engineer
Bayer AG
Leverkusen, West Germany
John F. Lawson, Manager
Waste Treatment Operations
Mobay Chemical Corporation
Kansas City, Missouri 64120
INTRODUCTION
The elimination of nitrogen from wastewater effluents is becoming increasingly important in the
Federal Republic of Germany. High nitrogen loads in surface waters create several problems, a few
of which are mentioned below:
1. An increased supply of NH, and NO; in standing waters promotes plant growth and can lead to eu-
trophy.
2. The greater part of ammonia nitrogen NH J - N in flowing waters is converted into nitrate. The oxygen
required for this biological process is extracted from the water. Reduction of oxygen content to less
than 4 mg/1 leads to a threat to fish stocks. The higher the water temperature, the more rapid this
process becomes and the more serious are its consequences.
3. Al pH values over 7, the ratio of ammonia NH, to free ammonia NH, shifts in favor of the free
ammonia, which has a toxic effect on fish and other aquatic organisms. The toxicity limit of ammonia
is in the region of 0.2 to 2 mg/1 for fish, and 0.2 to 9 mg/1 for other aquatic animals. Our studies have
confirmed previous reports that high ammonia content fluctuations inhibit the nitrification process.
4. The quality of drinking water is, however, primarily threatened by high nitrate and nitrite concentrations caused by farming. In the last 30 years, the quantity of mineral fertilizers used in the Federal
Republic of Germany has increased from 25 kg N/ha (22 lbs N/acre) to 120 kg N/ha (107 lbs N/acre),
that of organic fertilizers has risen from 40 kg N/ha (36 lbs N/acre) to 70 kg N/ha (62 lbs N/acre),
giving a total increase of over 300^0.
Conventional biological wastewater treatment plants have aeration basins with a water depth between 2.5 m (8 ft) and 8.0 m (26 ft). Bayer AG has developed a process where the water level in the
aeration tank is usually between 8 m (26 ft) and 25 m (82 ft). This great depth of water is the reason
for naming the process "Bayer Tower-Biology". A simplified flow-sheet of the process is shown in
Figure 1. The centerpiece of Tower-Biology is the injector developed and optimized by Bayer. This
is a two-phase injector which utilizes the kinetic energy of the water jet to efficiently disperse the air
flow into extremely fine bubbles.
OXYGEN TRANSFER
The laws of physics state that the oxygen yield in kg 02/hr is dependent not only on the interface
between the gas or air and the liquid but also on the concentration difference.
Oxygen transport in the gas/liquid system is described by the following relationship:
G/V = K a A Cm (1)
where:
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