24    DAIRY WASTEWATER TREATMENT WITH A
TEMPERATURE-PHASED ANAEROBIC SEQUENCING
BATCH REACTOR SYSTEM
Prince Dugba, Research Assistant
Ruihong Zhang, Assistant Professor
Biological and Agricultural Engineering Department
University of California
Davis, California 95616
Richard R. Dague, Professor
Civil and Construction Engineering Department
Iowa State University
Ames, Iowa 50010
ABSTRACT
Three two-stage anaerobic sequencing batch reactor (ASBR) systems were used to treat dairy
wastewater in the laboratory to evaluate a two-stage thermophilic-mesophilic system against a
two-stage mesophilic-mesophilic system. The total working volume of 15 liters for each system
was divided between the first- and second-stage reactors in the volume ratios of 1:4, 1:4, and 1:2
for the three systems, respectively. All three systems were automated to obtain precision feeding,
decanting, and data collection using a computer-based control and data acquisition system. Organic loading rates of 2, 3, and 4 g VS/L/day were tested at the system hydraulic retention times
of 3 and 6 days. The volatile (VS) removal varied from 26 to 44% with the thermophilic-
mesophilic systems destroying 26-50% more VS than the mesophilic-mesophilic system. No
fecal coliforms were detected in the effluents from the thermophilic-mesophilic systems compared to only two log reduction in fecal coliforms with the mesophilic-mesophilic system.
INTRODUCTION
Farm animals in the U.S.A. generate an estimated 2 billion tons of solid waste annually,1 some
nine times that generated from American homes. Traditionally, this waste is disposed of through
land application. In California, for example, about 90% of animal manure is applied to the land
with little or no pretreatment. However, increasing environmental awareness and dwindling agricultural land force farmers to look for efficient waste treatment alternatives. One promising alternative is the use of an anaerobic digester system to stabilize the waste for odor control and to recover energy and nutrients.
Most conventional digesters are continuously-stirred tank reactors (CSTR) with hydraulic retention time (HRT) equal to the solid retention time (SRT). In a CSTR. active biomass is easily
washed out with the effluent when the HRT is too short. The HRT has to be long enough (15 to
20 days) to maintain a viable bacteria population necessary to complete the anaerobic digestion
process. High-rate reactors such as the upflow anaerobic sludge blanket (UASB). the anaerobic
biofilter, and the fluidized bed reactor developed to improve biomass retention have shown better
treatment of dilute wastes compared to the CSTR. The HRTs can be on the order of several hours
to a few days compared to 15 to 20 days for the CSTR. Most of these high-rate reactors, however, require inert media placed in the reactors to support the bacterial growth. Uniform feed distribution requires special manifold designs that are difficult to maintain with high-solid wastewater. Clogging of the sludge blanket or the media matrix could be a problem when treating a
52nd Purdue Industrial Waste Conference Proceedings. 1997. Ann Arbor Press, Chelsea. Michigan 48118. Printed in
U.S.A.
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