62    APPLICATION OF THE TWO-PHASE ANAEROBIC
FLUIDIZED BED PROCESS TO THE TREATMENT OF
CORN PROCESSING WASTEWATER
Dilip J. Kothari, Development Engineer
Alan Y. Li, Technology Manager
Dorr-Oliver, Inc.
Stanford, Connecticut 06904
Thomas J. Kontol, Environmental Mgmt. Supervisor
American Maize-Products Company
Hammond, Indiana 46320
INTRODUCTION
The corn wet milling industry processes corn to produce starch, oil, corn syrup, and animal feed.
Normally, clean corn is steeped in a dilute solution of sulfuric acid to loosen the hull, soften the
gluten, and dissolve minerals or organic matter in the kernel. Next, the corn is coarsely ground and
cycloned to separate the germ from which oil is extracted. The kernel residue is finely ground and
screened to separate the soluble starch and gluten from the fiber and hull, which are used as feed
additives. Starch is centrifugally separated from the gluten and marketed either as starch, modified
starch, or hydrolyzed into corn syrup or corn sugar. Gluten is also used as a feed additive. Both the
feed-producing and starch-manufacturing process evolve a process wastewater containing approximately 1% of the corn in soluble form. Reuse programs, which are known as "bottling up," have
reduced plant losses to less than 0.5% of the dry corn raw material.
Major wastes from corn processing plants include the volatile organics entrained in the evaporator
condensate resulting from the evaporation of steep water, sweet water resulting from refining of corn
syrup and dextrose, starch filtrates from the preparation of modified starches, and wastes from
"bottling up" processes [1]. Other in-plant liquid waste sources will vary depending on the products
made and processes used in a particular plant [2].
The Hammond, Indiana corn processing plant of American Maize-Products Company manufactures modified and unmodified starches, corn syrups, corn syrup solids, dextrins, and feed co-
products. Corn processing waste streams can include steep water condensates, sweet water, starch
filtrates, carbon regeneration water, and gluten. These waste streams are currently disposed of in two
ways:
1. A major portion of the corn processing wastewater is treated in an on-site system
consisting of activated sludge and polishing lagoons, chemical treatment, and final
clarification. After clarification, the effluent is discharged to Lake Michigan. Waste
activated sludge (WAS) from the aerobic system is thickened and removed by centrifu-
gation.
2. At times, waste streams, representing a significant organic load, are sent directly to the
Hammond, Indiana publicly-owned treatment works (POTW).
The Hammond POTW sewer charges, assessed on flow, 5-day biochemical oxygen demand (BOD5)
and total suspended solids (TSS), are very significant. American Maize has investigated various
alternatives to reduce sewer charges and to reduce the load on its existing aerobic system. Among
these alternatives are product recovery, hauling away raw wastewater for disposal elsewhere,
expanded aerobic treatment capacity, and anaerobic pretreatment. Anaerobic pretreatment has been
chosen as the most cost effective and practical option.
Anaerobic pretreatment has proven to be a very attractive means of removing large quantities of
organic material from highly concentrated waste streams prior to on-site aerobic treatment [3] or
discharge to a local POTW. Significant reductions in aeration power costs or sewer surcharges can be
achieved with anaerobic pretreatment as well as production of large quantities of methane-rich
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