90    TREATMENT OF PORK PROCESSING WASTEWATER IN A
COVERED ANAEROBIC LAGOON WITH GAS
RECOVERY
Richard R. Dague, Professor and Chairman
Department of Civil and Construction Engineering
Iowa State University
Ames, Iowa 50011
Robert F. Urell, Vice President of Engineering
Eugene R. Krieger, Environmental Engineer
FDL Foods, Inc.
Dubuque, Iowa 52001
INTRODUCTION
The anaerobic lagoon process has been used in wastewater treatment for nearly 50 years. The first
deliberate application of the process was reported to be at Werribee in Australia in 1940.' Among the
earliest applications of the anaerobic lagoon process to meat packing wastes was by the Swift Company beginning in 1955.2
The anaerobic lagoon process is well known for its ability to provide a high degree of stabilization
for high strength wastes through methane fermentation.3"7 In most previous applications, anaerobic
lagoons have been designed and operated as open ponds, relying on a natural grease cover to reduce
exposure to the oxygen and temperature of the ambient atmosphere. Of course, gases and vapors
generated in the open system are released to the atmosphere.
Open anaerobic lagoons have worked well in the past in pretreatment for biochemical oxygen
demand (BOD) and suspended solids (SS) reduction. However, in some locations the direct release of
gases and vapors to the atmosphere is not acceptable. Problems arise from odorous gases (hydrogen
sulfide) and volatile organics (acids, aldehydes, ketones, mercaptans, etc.) that are sometimes generated in anaerobic environments.8
The purpose of this chapter is to describe the covered anaerobic lagoon treatment facility constructed by FDL Foods, Inc. at the company's pork slaughter and meat processing facility in Dubuque, Iowa, and to present and interpret data that reflect performance of the facility during 1987 and
1988.
BACKGROUND
Anaerobic Lagoons
As indicated previously, anaerobic lagoons have been used in wastewater treatment for nearly 50
years. The process has been particularly popular for pretreatment of livestock slaughtering wastewaters in the United States. Numerous reports describing the design and performance of anaerobic
lagoons have appeared in the literature. One of the most valuable papers was that of Hammer and
Jacobsen in 1970.9
In terms of anaerobic lagoon loadings and performance, little has changed in recent years. In their
1970 paper, Hammer and Jacobsen made the recommendations and observations listed below:9
1. Anaerobic lagoons should be constructed as deep as possible with minimum surface area.
2. A complete cover of accumulated grease is essential for good digestion to occur in an anaerobic
lagoon.
3. A well-operating anaerobic lagoon does not create serious odor problems. However, a high
sulfate ion concentration in process water can cause serious hydrogen sulfide odors.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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