The Treatment of Toxic Industrial Wastewaters
By A Two Step Process
ALLAN R. WILHELMI, Industrial Application Engineer
ROBERT B. ELY, Manager of Industrial Sales
Zimpro, Inc. (Division of Sterling Drug)
Rothschild, Wisconsin 54474
INTRODUCTION
The objective of this paper is to describe the applicability and flexibility of an
environmental engineering unit process called "Wet Air Oxidation" to the treatment of a
large class of industrial wastewaters which do not readily lend themselves to treatment by
other means. For this "class," biological treatment is either impossible or extremely difficult
because the wastes are biologically refractory or are toxic to treatment organisms.
Incineration is likely to be uneconomical in light of present energy costs because the flow is
high and/ or the waste is dilute. Further, incineration might be impractical if an air pollution
problem is created. These factors together with the pressure to abandon deep well and ocean
dumping as disposal means are causing more attention to be focused on wet air oxidation as
a viable treatment alternative.
The process of wet air oxidation is well established; more than 120 Zimpro Inc. wet air
oxidation units are either in operation or under construction throughout the world. A
number are dedicated specifically to the treatment of problem industrial wastes. Included in
this category are the wastes from the manufacture of acrylonitrile, monodosium glutamate,
polysulfide based rubbers, metallurgical coke, petrochemicals, and pharmaceuticals.
Although wet air oxidation alone may be used as the complete treatment process it is
often uneconomical to achieve the typically required 99+% reductions in a single step.
Instead, a two-step approach can be effectively used; the first, wet air oxidation
accomplishing 50-95% COD reduction, the second, a biological or biophysical polishing
step. The emphasis of this paper will be to demonstrate the compatibility between wet air
oxidation and biological treatment and in particular biophysical treatment.
WET AIR OXIDATION
Almost any material that is subject to oxidation — biological, chemical, or thermal —
can be oxidized at relatively low temperatures, under water, in the presence of air. Wet air
oxidation should not be confused with submerged combustion in that temperatures in the
wet air oxidation process rarely rise above 400 to 600 F and no flame is involved.
Figure I shows the basic elements of a wet air oxidation flow scheme. Wastewater
containing some oxidizable material is pumped through an exchanger. There the
temperature is increased to a point at which the reaction between the oxidizable material
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