Full Scale Pilot Plant Studies of a Sub-Surface
Mixing and Aerating System for Treatment of
Cannery Wastes
WALTER W. ROSE, Section Head
Water and Waste Engineering
National Canners Association
Berkeley, California
ALEX GRINKEVICH, Project Engineer
Hunt-Wesson Foods
Fullerton, California
INTRODUCTION
An essential part of any aerobic treatment system is the method of maintaining
dissolved oxygen in the wastewater. The simplest form of maintaining aerobic
conditions is to rely on oxygen transfer from the air to the surface of the water. This
method of aeration limits the organic loading of the treatment system because of the
limited rate of oxygen transfer.
An improvement in the aerobic treatment system has been the practice of
introducing air below the surface of the water. Oxygen is transferred to the liquid as
the bubbles rise to the top surface. In recent years, surface aerators have been
developed to provide oxygen for aerobic systems. In general, the aerators pull up the
liquid and throw it out into the air where the oxygen transfer takes place.
Recently, another type of aeration was developed which combines the
principles of surface aerators and diffused aeration. The aeration unit, known as a
Helixor, was developed in Canada. In 1970, a cooperative study was undertaken to
evaluate, on a pilot scale, the treatment of tomato wastewater.
The Helixor, shown in Figure 1, consists of an 18 inch diameter extruded
polyethylene tube (B) and a monolithic helix (C) of designed pitch to divide the tube
longitudinally into two separate sections. At the bottom opening of the tube,
compressed air (D) is introduced through two orifices (E), one on either side of the
helix component. The Helixor is anchored (A) in a vertical position on the bottom of
the aeration basin. The submerged unit has no moving parts and is completely
maintenance free.
The air rising inside the vertical tube causes the water to flow upwards. The
mixture of air and water follows the spiral passage of the helix, prolonging the
interfacial contact between the small air bubbles and the liquid. As the flow is very
turbulent, maximum oxygen transfer is ensured.
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