Enzyme Activity as a
Parameter of Digester Performance
F. J. AGARDY, Assistant Professor of Civil Engineering and Applied Mechanics
San Jose State College
San Jose, California
R.  D. COLE, Associate Professor, Department of Biochemistry
University of California
Berkeley, California
E. A. PEARSON, Professor of Sanitary Engineering
University of California
Berkeley, California
Wastes have been degraded by aerobic, anaerobic and faculative organisms
since the beginning of recorded history and the "engineering" of units to perform
this degradation has been practiced for many decades. However, knowledge regarding the responsible organisms, biochemical mechanisms and process kinetics
is still at an elementary level. Although much of the ignorance can be attributed
to the heterogeneous, complex and variable nature of both the waste material-and
the flora and fauna ofthe treatment process, the result has been design and operation by trial and error. This is especially true of anaerobic sludge digestion systems where nature of the substrate allows description only in general physical and
chemical terms.
Many researchers believe that to understand the mechanisms of biological
waste treatment systems it is necessary to define the process kinetics. There is
certainly no quarrel with this approach. However, kinetic studies are hampered
by the difficulty in measuring the "active" organism concentration and the complete lack of information about enzyme activities in mixed population biological
systems. This void concerning enzyme activity and its measurement makes close
control of a system difficult and prevents systematic evaluation of rate-controlling,
enzyme-catalyzed reactions in the waste degradation chain.
The research reported herein was an attempt to develop a relatively simple
method for enzyme activity measurement and thereby allow digestion conditions
to be evaluated accurately.
ENZYME ACTIVITY AS RELATED TO ANAEROBIC DIGESTION
It is well established that reactions occurring in a waste fermenter are enzyme catalyzed and that these enzymes are in fact "agents" of bacteria. From
a waste treatment of stabilization standpoint, it may be well to indicate the general preference of bacterial performance or efficiency:
1. A bacterial cell should utilize the substrate for maximum growth and reproduction and in so doing produce a minimum of decomposable and a maximum
of nondecomposable waste or by-products.
2. Under conditions of stress, such as changes in organic loading, pH, temperature,   alkalinity,  etc.,  the cell should adjust rapidly to the new environment,
particularly with respect to enzyme production and activity,   or in other words,
rapidly reach a new steady state condition.
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