Stabilization of a
Low Solids Carbohydrate Waste by an
Anaerobic Submerged Filter
ALAN H. PLUMMER, JR.. Engineer-in-Training
Brown and Root, Inc.
Houston, Texas
JOSEPH F, MALINA, JR., Associate Professor
W. WESLEY ECKENFELDER, JR., Professor
Civil Engineering Department
University of Texas
Austin, Texas
INTRODUCTION
The anaerobic stabilization of a food processing carbohydrate waste by means
of submerged anaerobic filters was evaluated in this investigation. This process
is particularly applicable to wastewaters which contain a high concentration of
dissolved organic matter and low suspended solids content because of the long
biological solids retention time (SRT) possible. The bacteria responsible for
waste stabilization tend to grow on the walls of the confining structure as well as
to the solids media and remain in the system for a relatively long time. The
media also acts as an obstacle that prevents "washout" of the microbial solids
located in the voids of the media. This paper discusses the development of the
anaerobic filter and presents some of the results observed during a laboratory
study (1).
DEVELOPMENT OF ANAEROBIC SUBMERGED FILTER
The complex reactions of waste conversion and stabilization that take place
in the anaerobic process involve the liquifaction of the solid organic matter and
the hydrolysis of complex molecules followed by the conversion of the solubilized
material to organic acids which are sequentially converted to carbon dioxide and
methane gases. Obviously, success of the process is dependent on the presence of
both acid-producing and methane-producing bacteria. The fact that bacteria
cell production is less in anaerobic treatment than in aerobic treatment, would be
a definite incentive to utilize this type treatment. This lower cell production
results in smaller quantities of sludge that require disposal, and it reduces the requirements of biological nutrients. Although this low cell production is an advantage, it can cause problems in the continuous anaerobic treatment of liquid
wastes. Failure of the process can occur because of the "washing out" of the
microbial population. This fact stresses the importance of a long.solids retention
time. Solids retention time (SRT) is defined as the mass of SSin the unit divided
by the mass of SS removed from the system per day. It is necessary to have all
minimum SRT that equals the generation time of the methane-producing bacteria
which are necessary for anaerobic treatment and which have much longer generation times than do the acid-producing bacteria.
The anaerobic contact process involves a digester or reactor followed by a
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