Jet Aeration Theory and Application
JERRY Y.C. HUANG, Chief Application Engineer
MIKKEL G. MANDT, Director of R & D
Penberthy/ Houdaille Industries, Inc.
Prophetstown, Illinois 61227
INTRODUCTION
Aeration is a process by which a gas is transferred into a subsaturated liquid. In the
activated sludge process, the purpose of aeration is to efficiently dissolve oxygen into mixed
liquor as well as to keep mixed liquor suspended solids in suspension. Aeration devices are
continuously being developed. In a very general sense, they can be classified into four
categories. They are mechanical aerator, sparge-turbine, air diffuser, and jet aerator.
Jet aeration is an aeration system which utilizes apparatus for directing a stream or jet
of gas/ liquid mixture into the aeration basin to increase the oxygen content. The jet aerator
has evolved from the ejector aerator, which has been used since the 1940's. The former
inherits the advantages but not the disadvantages of the latter.
In the early period, the largest installation of ejector aerators was the waste water
treatment plant at Dow Chemical (1,2,3) and at Farbenfabriken Bayer, Leverkusen, West
Germany (4). The process of aeration by ejectors in the activated sludge unit was patented
by Powers (3). Based on the result of research at Pennsylvania State University, Kountz(5)
used ejectors in an activated sludge process treating dairy waste water. Recent works of
West and Paulson (6), LeCompte and Mandt (7) and Wilson (8,9,10) explore the
fundamental principles of jet aeration and its applications. In this paper, basic principles as
well as system design application will be included.
OPERATING PRINCIPLES
An ejector is a jet device which usesan operating fluid at a high pressure to entrain a
suction fluid at a low pressure, discharging the mixture of motive and suction fluids against
an intermediate pressure. Ejector aeration is one of the applications by which ejectors are
operated as a unit process. In ejector aeration, compressed air is mixed with mixed liquor
and/ or returned sludge under pressure at the exit of the jet nozzle. The ejector aerator is
located near the bottom of the aeration tanks where the discharging mixture of fluid and air
gives the maximum oxygenation and agitation.
NEW JET AERATOR
From previous works and operating experience, some findings concerning the ejector
aeration system can be summarized:
1. High oxygen absorption efficiency and high oxygenation capacity (1,2,3,4,5,7)
2. High mixing capability (3,7)
3. Increased floe settleability (3)
4. Clogging problems due to small nozzle size (2)
In 1970, a new jet aerator evolved from the ejector aerator. Seeking a low cost and low
maintenance ejector aeration system. Wilson (10) enlarged the jet nozzle to greater than one
inch and eliminated the diffusion section of the ejector.
An individual jet flow which creates turbulence in the surrounding fluid is illustrated in
Figure 1. Since mass and material are transported in all directions by the mixing process of
the turbulence, it follows that the turbulence will spread in all directions in a flow stream. As
shown in Figure I, near the boundary of the jet flux where high velocity flow is adjacent to
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