Sludge Activity Parameters and Their
Application to Toxicity Measurements and
Activated Sludge
JAMES W. PATTERSON, Graduate Student
PATRICK L. BREZONIK, Assistant Professor
HUGH D. PUTNAM, Associate Professor
Department of Environmental Engineering
University of Florida
Gainsville, Florida
INTRODUCTION
The inadequacies of activated sludge operation control parameters have long
been recognized by waste treatment researchers and plant operators. Use of inappropriate monitoring methods for treatment unit degradation capabilities results
in operation incompatible with both present legislative requirements for high quality
effluent and economic requirements for high efficiency. This paper will briefly
review some of the advantages and disadvantages of the standard tests, and then
discuss several other more specific biochemical parameters, particularly with regard
to their applicability to activated sludge systems under toxic stress.
CURRENT MONITORING TESTS
Current biological control (or monitoring) tests used in biological waste treatment may be divided into three categories:
1) Unit operation efficiency:   BOD reduction and COD reduction;
2) Biological population density:  ML VSS and SVI;
3) Biological oxidative capacities:     sludge age, sludge yield (lbs sludge produced x 100/lbs BOD removed), rate of BOD exertion as indicated by the
first order rate constant, k..
The appropriateness of BODr reduction or COD reduction as treatment efficiency parameters has been discussed at length in the literature (1,2,3). The time
required to run the standard BOD test presents the most obvious difficulty. In addition, BOD measurements on the treatment unit influent and effluent only approximate unit efficiency because of the different k, values for BOD exertion of influent
and effluent, and the flow detention time within the unit. The COD test circumvents
some of the disadvantages of the standard BOD test, but itself is considered unacceptable by many who question the relationship between material oxidizable under
strong acid and high temperature conditions and material oxidizable by microorganisms under physiological circumstances. It is not our purpose to discuss at length
the relative merits or deficiences of these two tests. However, it is pertinent to note
that an extensive comparative study (2) on a synthetic waste showed a standard deviation for the BOD test of approximately 20 per cent, while the corresponding value
for the COD test was only eight per cent. Furthermore, Symons et al (3) concluded
that the change in soluble COD through an activated sludge pUot plant shows what
portion of the oxidizable material removed is due to biological action, even though
single COD determinations may not be directly related to the biodegradability of a
waste.    These conclusions were based on pilot plant studies of industrial waste
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