Soybean Processing — Oil Refining Wastewater:
Characteristics and Treatment
DEWEY R. ANDERSEN, Associate Professor
Department of Civil Engineering
University of Nebraska
Lincoln, Nebraska
RONALD E. BENSON, Chief
Water Pollution Division
Department of Environmental Control
State of Nebraska
Lincoln, Nebraska
JAMES A. LOFTON, Sanitary Engineer
City of Omaha
Omaha, Nebraska
THOMAS T. SATCHELL, Engineer
Hennington, Durham, and Richardson, Inc.
Omaha, Nebraska
INTRODUCTION
Soybeans are believed to have originated in China where written records on soybean
production date back to 2800 B.C. They were not grown in the United States until 1804,
however, and the first recorded milling of soybeans for oil in the United States occurred in
North Carolina in 1915 (1). Because of their varied uses, high nutrient value and
adaptability to modern farming techniques, soybeans now constitute one of the major
agricultural crops in the United States.
Soybean processing involves extracting oil from the beans, milling the spent bean
flakes and refining the oil. In this paper, the characteristics and treatability of the process
wastewaters are discussed. Data presented were obtained from a study of a 60,000 bushel
per day plant which is located in Lincoln, Nebraska and is operated by Archer-Daniels-
Midland Company (ADM), Inc. Daily oil production in the plant is 600,000 to 700,000
pounds. Except for occasional maintenance and repair necessitating plant shut down, the
plant operates on a continuous basis, as is typical for this industry. After pretreatment,
process wastewater is discharged into the municipal sewerage system and is treated in an
aerated-aerobic waste stabilization lagoon system serving northeast Lincoln.
The study involved laboratory analyses to determine the characteristics of the
wastewater, a laboratory evaluation of the aerobic treatability of the wastes and a field
study of the lagoon system. The sections of this study are presented in this order.
SOURCES AND CHARACTERISTICS OF PROCESS WASTEWATERS
The first step in processing soybeans involves cleaning, cracking and removing the
soybean hulls, steaming the bean meats to provide a uniform moisture content and rolling
the meats into flakes to facilitate the extraction of oil. Since this preparation step involves
only dry processes, no liquid wastes are produced if dry cleaning of dust, etc. is provided.
Next a solvent (hexane) is used to extract the oil from the flakes in an extractor unit.
Spent flakes pass through a desolventizer toaster, where the retained solvent is stripped
from the flakes with steam, prior to being ground and blended with hulls for soybean meal
or other desired products. Solvent from the extractor unit, which contains approximately
25 percent oil and is called miscella, is directed to evaporators where the crude oil is
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