Pharmaceutical Waste Treatment
With an Anaerobic Filter
NORMAN D. DENNIS, JR., 2nd Lieutenant
S-2, 52nd Engineers Battalion
Ft. Carson, Colorado 80913
J. CHARLES JENNETT, Associate Professor
Department of Civil Engineering
University of Missouri — Rolla
Rolla, Missouri 65401
INTRODUCTION
Anaerobic treatment of organic wastes has a number of advantages which make it a
more desirable treatment process than either aerobic or chemical methods. The prime
advantages are that a high degree of waste stabilization can be accomplished with a
relatively low production of biological solids, and a usable by-product, methane gas, is
produced in the process. In addition, the need for costly aeration equipment is eliminated,
and the size of sludge disposal equipment required for aerobic or chemical systems is
reduced.
The principle disadvantage of using an anaerobic process is the relatively low
conversion of organic matter to cell mass, particularly the sensitive methane formers. This
low conversion factor results in problems of developing enough cell mass to treat the waste
and provide system sensitivity for shock loadings. The development of anaerobic activated
sludge and other similar contact processes has alleviated many of the problems associated
with anaerobic digestion. According to McCarty (I), the process has provided reasonably
adequate treatment for both low and high strength wastes, because a large population can
be maintained by sludge recycling.
An important operating parameter in these systems is the solids retention time (SRT).
At long SRTs, sufficient microbial mass can be established for efficient treatment. With the
anaerobic contact process almost complete solids separation and recycle is required to
provide an adequate SRT for effective treatment. An ideal process would then be one which
is able to retain biological solids independent of the waste flow and simultaneously
maintain these solids for long periods of time. Studies using the "anaerobic filter" have
indicated that a process is available to treat soluble wastes efficiently without the need for
solids recycle.
Satisfactory results were obtained in an exploratory study by McCarty (2) with a 3-1
anaerobic filter containing 1 to 2 inch (2.54 to 3.08 cm) quartzite gravel. With this process
the waste was passed upward through the gravel bed allowing the biological solids to
become attached to, or trapped within the interstices. This configuration provided adequate
solids for treatment and prevented the solids from being carried out in the effluent stream.
The filter was operated for 307 days while receiving methanol, acetate, and propionate, as
pure or mixed substrates at concentrations of approximately 2,000 mg/1 COD. Removal of
COD for 12 hours detention times averaged 81 percent, with effluent solids usually below 20
mg/1. The average SRT in this filter was estimated to be over 100 days.
Young (3) conducted the first intensive investigation of the anaerobic filter. In his
study, eight, 1 cu ft (28.5 1) laboratory filters were subjected to a varied range of organic and
hydraulic loadings while acetic acid and nutrient broth were employed as the substrates.
COD loadings from 375 to 12,000 mg/1 and detention times from 4.5 to 72 hours produced
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