Document Type


Date of Award


Degree Name

Master of Science in Environmental Engineering - (M.S.)


Civil and Environmental Engineering

First Advisor

Gordon Lewandowski

Second Advisor

Basil Baltzis

Third Advisor

Carol A. Venanzi


Mixed liquor suspended solids (MLSS), oxygen uptake rate (OUR) and general dehydrogenase activity, as expressed by the reduction of the electron-acceptor Dye 3-(4',5'-dimethylthiazol-2-yl)-2, 4-diphenyltetra-zolium bromide (MTT), were compared for their ability to measure microbial activity in mixed aerobic cultures. A fourth parameter, specific enzyme activity, was dropped from consideration because of the difficulty of developing a satisfactory experimental technique. Measurement of the parameters was applied to the biodegradation of phenol and o-chlorophenol by activated sludge from a municipal sewage treatment plant, and by two commercially available bacterial preparations.

MLSS, although the most commonly used of the three parameters tested, is often irrelevant to the true microbial activity and is therefore inappropriate for use as a metabolic parameter.The reduction rate of MTT is potentially useful as a metabolic parameter, but requires a more complex preparation and provides less reproducible results than OUR. OUR has the clearest demonstrable relationship to substrate removal rate and provides the most reproducible results. Substrate removal rates that are normalized with respect to OUR are much more consistent than the original SRR data. OUR can be readily measured using an electrochemical probe, making it the easiest technique to apply.



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