2    EVALUATION OF THE OXYGEN TRANSFER
CHARACTERISTICS OF AERATION SYSTEMS
OPERATING IN THERMOPHILIC
TEMPERATURE RANGES
Brion F. Wynn
Walter V. Linden, P.E.
Robert C. Backman
WATERLINK Mass Transfer Systems, Inc.
Fall River, Massachusetts 02723
ABSTRACT
There has been a large volume of research on oxygen transfer which has helped to define factors affecting the design of aeration systems. There are, however, many misconceptions regarding the effects that high liquid temperatures have on the oxygen transfer process in both clean
water and biological reactors. This chapter will discuss the effect of various mesophilic and thermophilic temperatures on dissolved oxygen saturation concentrations (beta factor), the overall
mass transfer coefficient (alpha factor), and the temperature correction coefficient (theta factor).
The operating performance of jet aerators over the past 12 years in both thermophilic activated
sludge processes and autothermal thermophilic aerobic digesters will be discussed. In addition,
the results of a performance evaluation of jet aerators and membrane diffusers will be presented.
This comparison will show the oxygen transfer characteristics of the two devices operating in
different temperature ranges.
Ongoing research by Mass Transfer Systems is being carried out to further define the effect of
various components of the aerobic treatment on oxygen transfer performance. This is a continuation of previous work conducted in conjunction with Northeastern University1-2 and now being
continued in association with Purdue University.6
INTRODUCTION
Over the past 12 years, various full scale oxygen transfer systems in industrial effluent biological processes or thermophilic aerobic digesters have exhibited excellent performance in terms of
mass transfer per unit kW. These aeration systems are typically installed in activated sludge
processes or autothermophilic aerobic digesters (ATADs) in the Pharmaceutical and Food Processing industries. In addition to exhibiting excellent oxygen transfer performance, these
processes have other similar features, such as: high COD concentrations, thermophilic temperature ranges, high TDS concentrations, tendency to foam (i.e., low surface tension), and very low
sludge production rates while operating at conventional F/M ratios.
It is believed that the relationship between thermophilic temperature, foaming, and low sludge
production are related. It would appear that the increased biological activity in these temperature
ranges promotes a high degree of endogenous respiration resulting in the breakdown of bacterial
cells into simpler components. In particular, the breakdown of protein results in the release of extracellular enzymes which tend to cause foam. The effect that this reduction in surface tension, in
conjunction with high TDS concentrations, has on oxygen transfer performance is the basis for
this ongoing research.
52nd Purdue Industrial Waste Conference Proceedings, 1997, Ann Arbor Press, Chelsea, Michigan 48118. Printed in
U.S.A.