Biological Degradation of
Wastes Containing Certain Toxic
Chemical Compounds
ROBERT H. L. HOWE, Sanitary Engineer
Eli Lilly and Company
Lafayette, Indiana
In the treatment of pharmaceutical production wastes, engineers, chemists, and biologists frequently encounter the problem of toxic chemical com -
pounds. Certain toxic chemical compounds are extremely dangerous to
humans and other animals, physiologically speaking. Others may actively
inhibit biological growths and the metabolism desired for the biological treatment of waste waters. They create problems by interrupting the function of a
biological waste treatment system.
The purpose of this paper is to present some actual problems and to discuss the author's experience in overcoming such problems of toxic chemical
compounds in waste waters. Experimental and applicational work has been
conducted since 1957. The toxic chemical compounds to be discussed in this
paper are primarily organic in nature. They include: certain potent antibiotics, certain phenol-mercury compounds, certain hormones, and others containing formaldehyde and methyl alcohol.
ANTIBIOTICS
It is well known that certain antibiotics are actually bactericidal and
others are only bacteriostatic. The effect of antibiotics on microbial growths
depends on many factors including pH, dosage, time, temperature, specific
organisms, and specific biological and biochemical conditions which control
the stability of the particular antibiotics. In many cases, a very small dosage
of antibiotics added to the liquid may become sufficient to inhibit certain
micro-organisms (Table I) (1),(2),(3). However, it requires a much higher
concentration of antibiotics to inhibit the micro-organisms in a biological
oxidation system for wastes treatment because many types of micro-organisms
exist.
When the antibiotic concentration in the biological oxidation system
reaches the toxic level, it is frequently noticeable that the biological floes
become dispersed or disintegrated. If the toxic level can be maintained by
the antibiotics for a prolonged time, the microbial population gradually decreases. On the other hand, if the concentration of antibiotics is reduced, the
microbes in the aeration system may tolerate the presence of antibiotics for
some time and then become resistant to it. Consequently, a gradual increase
of microbial population may be on the way and finally the antibiotic potency (concentration) gradually disappears. If the biological oxidation system
receives only a certain amount of antibiotics continuously, a gradual increase
of antibiotics concentration may not interfere with the microbial metabolism
as the microbes have undergone a gradual process of acclimation in the presence of certain antibiotics. However, it must be pointed out that whereas
micro-organisms in the biological oxidation system may be successful in their
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