EVALUATION OF OXYGEN TRANSFER COEFFICIENTS
OF COMPLEX WASTEWATERS
Sara J. Bass, Process Engineer
Calgon Environmental Systems Division
Calgon Corporation
Houston, Texas 77092
Gerry L. Shell, President
Gerry Shell Environmental Engineers
Brentwood, Tennessee 37027
INTRODUCTION
The majority of the wastewater treatment facilities being built today depend upon aeration systems for the biooxidation of pollutants. With the capitol and operating costs of such
systems rising almost daily and the penalities for the underdesign of systems a painful reality,
there is a real need for methods of accurately predicting what the transfer efficiency of an
aeration system will be under field conditions. At present, most manufacturers rate the oxygen transfer efficiency of their aeration equipment in tap water under standard conditions
(e.g., 20 C, zero DO and at sea level). The design engineer must correct the manufacturer's
rating to actual field conditions. In making this correction there are five coefficients and
values that must be either determined experimentally or assumed:
1. The oxygen transfer efficiency correction coefficient, a.
2. The temperature correction coefficient, 6.
3. The DO saturation correction coefficient for waste composotion, |3.
4. The DO saturation concentration for tap water under standard conditions, Cs.
5. The DO saturation concentration for wastewater at field temperature and
pressure, Csw.
Once these characters are in hand, they can be inserted into Equations 1 and 2 and the
horsepower requirements for an aeration system can be calculated:
S0R  .     r_    A0*     (1)
r^w-ci/i
20-T
Where    SOR   =   oxygen requirements for tap water at standard (manufacturers') test conditions,
lb02/hr
AOR  ■   actual oxygen requirements for aeration system (either calculated or determined
experimentally in a pilot system operated at field conditions), lb Oj/hr
T        =   design aeration basin temperature,  C
Cl      =   design dissolved oxygen concentration in the aeration basin, mg/1
S0R rw
hp ■ "hT (2)
Where   hp      =   horsepower required
N0      =   manufacturer's oxygen transfer rate for standard conditions, lb Oj/hp-hr
Once the total horsepower requirements are calculated, the power level, PL, is checked as in
Equation 3 to ensure sufficient horsepower for mixing:
basin volume in million gallons
953