54    ANAEROBIC SEQUENCING BATCH REACTOR TREATMENT
OF SWINE WASTES AT 20°C, 25°C, AND 35°C
Christopher G. Schmit, Graduate Research Assistant
Richard R. Dague, Professor of Environmental Engineering
Department of Civil Engineering
Iowa State University
Ames, Iowa 50011
INTRODUCTION
The waste generated in the livestock industry in the U.S. has an estimated population equivalent of
one billion people.' In Iowa alone, the population equivalent of livestock waste is about 100 million,
some 36 times the state's human population.) The trend in the swine industry to large confinement
facilities has caused environmental problems in the handling and disposal of generated waste. The
problems include not only offensive odors, but also threats to ground and surface water quality.
Anaerobic digestion is one way in which to dispose of swine waste. Anaerobic digestion occurs in
three stages with each stage holding its own consortium of bacteria. The hydrolysis stage breaks down
complex organic matter into simple, low molecular weight fermentation end products such as lactate,
ethanol, acetate, formate, H2, propionate, and butyrate.2 The acetogenic group oxidizes hydrolytic
fermentation end products into acetate, H2, and formate. The methanogenic group uses the end
products of the acetogenic group and produces methane and carbon dioxide gas.
In order for the completion of the above reactions the right conditions and proper nutrients must be
supplied. A lack of proper nutrients may lead to an imbalance in the digestion process. On the other
hand, too much of certain substances can cause inhibition or be toxic to the anaerobic process. The
composition of swine waste is shown in Table I.3
Swine waste contains a sufficient amount of nutrients for anaerobic digestion. Two compounds are
available in amounts that may be inhibitory. These two compounds are sulfides and ammonia.
According to McCarty, ammonia nitrogen levels between 1500 and 3000 mg/L can be inhibitory if the
pH is between 7.4 and 7.6.5 The inhibition level of ammonia relies greatly upon pH because pH
determines the form of ammonia nitrogen. Sulfides can be a problem and may be lowered by the
addition of iron salts that will precipitate the sulfides.
A suspended growth reactor needs to be used to handle swine waste in a reactor without the
separation of the solids before feeding. Studies on attached growth systems show good solids destruc-
Table I.    Typical Chemical Composition of Swine Waste (Dry Weight Basis,
Based on Total Solids)3
Component
Concn.
Component
Concn.
Cellulose, % TS
11.4
Sulfur, % TS
0.3
Hemicellulose, % TS
16.5
Copper, ppm
249.0
Lignin, % TS
69.0
Zinc, ppm
526.0
Protein, % TS
18.9
Iron, ppm
1940.0
Lipids, % TS
13.7
Aluminum, ppm
544.0
Total N, % TS
5.3
Manganese, ppm
342.0
NH3-N, % TS
2.2
Cobalt, ppm
6.1
Ash, % TS
14.0
Molybdenum, ppm
0.3
Calcium, % TS
3.2
Cadmium, ppm
1.0
Phosphorus, % TS
1.7
Lead, ppm
12.1
Potassium, % TS
0.9
Gross Energy
18.1
Magnesium, % TS
0.8
Content, MJ/Kg
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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