BIOLOGICAL TREATABILITY CHARACTERISTICS OF CORN AND
POTATO CHIP SNACK FOOD PROCESS WASTEWATERS
Suzanne H. Thorn, Project Engineer
Edward J. Reap, Group Manager
Engineering Department
Frito-Lay, Inc.
Dallas, Texas 75247
The manufacturing of snack foods, primarily corn and potato chips, results in a considerable amount of high strength process wastewaters. Medium to large snack food plants
which produce corn and potato chips as their primary products can be expected to generate
raw wasteloads on the order of 25,000 to 100,000 population equivalents. The location of
these plants oftentimes necessitates the construction of on-site biological treatment facilities
to adequately treat the resultant wastewaters prior to discharge.
A limited amount of data is available in the literature on the specific biological treatability characteristics of corn and potato wastewaters resulting from the snack food industry.
Previous investigations conducted by Frito-Lay, Inc., were successful in determining the
treatability characteristics of combined corn and potato wastewaters in complete mix
activated sludge systems for discrete operating conditions. The effect of temperature, the
influence of product mix and the interrelationship of settleability and loading rate were
not fully defined. Particular areas that will be addressed in this paper are the influence of
product mix and temperature on organic removal, oxygen utilization, sludge production,
settleability and effluent suspended solids.
SOURCES AND CHARACTERISTICS OF PROCESS WASTEWATERS
Wastewaters are generated from the manufacture of corn and potato products prior to
the actual frying operations. Typical production lines and the major sources of wastewater
generation are presented schematically in Figures 1 and 2.
Potato wastewaters result primarily from destoning, peeling and slice washing operations,
Figure 1. Potatoes are delivered to the plant by truck or railcar and stored on-site in a
climate-controlled warehouse. Potatoes received from storage first pass through a destoner
where mud and sand are removed. They then are peeled, sliced and washed prior to entering
the fryer. The sliced potatoes are then fried and packaged for sale.
Corn wastewaters result primarily from cooking, soaking and washing operations, Figure
2. Corn is typically delivered to the plant by railcar and stored in silos on-site. Corn received from storage is cooked in individual batches and then transferred into soaking vats.
After a prescribed period of time, the corn is removed from the soaking vats and the cooking
liquor (steep water) is discharged. The corn is then washed to remove the softened husk.
The corn is then ground, extruded, fried and packaged for sale.
The wastewaters resulting from these production techniques are high in organics and
solids. Organics are composed primarily of carbohydrate and protein materials. Solids are
comprised of sand, corn husks, potato slices and starch. The total BOD and TSS are on the
order of 3000 and 4000 mg/l, respectively. The wastewaters are slightly deficient in nitrogen
and phosphorus when related to a BOD/N/P ratio of 100/5/1 considered the minimum
necessary for treatment in biological systems. Oil and grease levels during production operations are typically in the range of 5 to 10 mg/l.
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