Pharmaceutical Waste Disposal Studies
II.  TURBINE MIXER AERATION IN AN ACTIVATED SLUDGE PLANT
WILLIAM G. BARKER, Chemical Engineer, Develpment Department
R. H. OTTO,  Research Microbiologist,  Research Department
D. SCHWARZ, Chemical Engineer, Engineering Department
B. C. TJARKSEN, Chemical Engineer, Chemical Manufacturing Department
Abbott Laboratories
North Chicago, Illinois
SUMMARY
This is the second part of a continuing program of study being conducted
at Abbott Laboratories to improve operation ofthe company waste treatment
facilities.
The following is a report on the performance of a sparged turbine mixer
aeration system installed in an activated sludge plant after successful and intensive studies in earlier pilot work (1). Sustained plant operation results have
demonstrated the ability to handle loadings up to 550 lbs of applied BOD per
day per 1000 cu ft of aeration tank volume with 75 to 85 percent BOD reduction. Air requirements have averaged 220 cu ft of air per lb of applied BOD.
Total power requirements including both mixer and air compressor horsepower
have ranged from 0.35 to 0.45 kwh per lb of BOD removed. Plant performance has fully confirmed the results obtained in the pilot plant.
HISTORY
The Abbott Laboratories process waste streams were previously treated in
a conventional activated sludge plant in which the aeration tanks were
equipped with hydraulic ejectors for air diffusion. It became apparent that
dissolved oxygen would become a limiting factor as the organic load to the
treatment plant increased. Reserve aeration capacity of the aeration equip -
ment had not been realized since the hydraulic ejectors tended to foul and
could not be kept at peak efficiency without repeated cleanings.
To maintain the waste treatment facilities ahead of continuing company
growth necessitated finding an improved method of aeration in existing tankage or building additional tanks of conventional design. Intensive pilot plant
studies were conducted from June 1957 to December 1957 to determine the
most effective means of increasing the treatment efficiency and capacity of
the existing plant waste treatment facilities. Based on the encouraging results obtained through the use of a sparged turbine mixer aeration system in
the pilot plant, it was decided to replace the existing plant aeration equipment with sparged turbine mixers.
DESIGN AND INSTALLATION
Optimum pilot plant performance had been obtained when the mixer
horsepower input was 0.8 hp per 1000 gal of aeration tank volume with 200
scfm of air per lb of BOD applied. Extrapolation to the main plant indicated
that 260 horsepower would be required to maintain the same power input in a
basin of 330,000 gal capacity. The combination of impeller speed and diameter was designed to draw 90 per cent of rated full load mixer motor current.
This would then allow for continuous operation under varying conditions of
liquid viscosity and mixed liquor solids concentration. Therefore, a total of
300 mixer hp was selected to operate at 90 per cent input. This was felt to be
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