OXIDATION OF A CORN-MILLING
WASTEWATER WITH HYDROGEN PEROXIDE
Darde deRoulhac, Graduate Student
Gary L. Amy, Assistant Professor
Department of Civil Engineering
University of Arizona
Tucson, Arizona 85721
Nathan C. Burbank, Jr., Private Consultant
Tucson, Arizona 85718
INTRODUCTION
In Tucson, Arizona, waste treatment plants have operated well for many years, and the whole
matter of industrial waste was taken for granted as part of simple acceptance of the wastes as domestic.
Our attention was drawn to a particular industrial waste, wet corn milling waste, because a very
small plant processing wastewater for application upon a golf course for irrigation purposes experienced operational problems. The plant, a small, conventional activated sludge plant (Smith and Loveless 1.0 MGD package plant) had operated for more than five years without difficulty. Suddenly, the
influent varied widely in pH and ORP, and there was generation of amounts of H2S to cause complaints in the neighborhood. The carriage water is high in sulfates and at low pH and low ORP,
hydrogen sulfide was generated in large amounts.
The industrial waste monitoring crew investigated the situation for several weeks, and they tracked
down many leads, all to no avail. One salient fact emerged that there were a number of food processors in the neighborhood, and in the greatest number were tortilla manufacturing plants.
The tortilla factory is characteristically a family enterprise, usually founded in the kitchen of a
forebear, and it grew as the community enlarged until today, Tucson and other communities with Hispanic-Indian roots in the Southwest have a number of these establishments processing several tons of
corn (as well as wheat flour) each day.
In Tucson, we have ten plants. These vary in size from the local neighborhood unit manufacturing
a few hundred dozen (300 dozen/day) to large plants serving the entire region with thousands of
dozens (83,000 dozen/day).
Without the tortilla there would be no tacos, enchiladas, tostadas or other standard Mexican delicacies which comprise the $350 million Mexican food market. It is estimated that Americans will eat
approximately three billion of these tortillas this year.
Manufacture
Corn is the basic material in tortillas. The best tortilla corn comes from the Southwest U.S.A.
where the ears of corn are dried naturally in the fields where they are grown under conditions of naturally low humidity (8-10% relative humidity) and temperatures of 75 to 108 F.
The white corn kernels, husked and removed from the cob, are rinsed in cool, fresh water and
piped to cooking vats where a small amount of lime is added along with more water. The lime softens
the tough outer hull so that it can be removed.