33    ANAEROBIC TREATMENT OF SWINE WASTE BY
THE ANAEROBIC SEQUENCING BATCH REACTOR
Ruihong Zhang, Assistant Professor
Department of Biological and Agricultural Engineering
University of California at Davis
Davis, California, 95616
Yulin Yin, Graduate Assistant
Shihwu Sung, Associate Scientist
Richard R. Dague, Professor
Department of Civil Engineering
Iowa State University
Ames, Iowa 50011-3232
INTRODUCTION
Anaerobic treatment is a technology well suited to helping solve the serious environmental and
social problems associated with animal wastes produced as by-products of animal enterprises.
An anaerobic treatment system can be easily integrated into liquid waste handling systems which
are commonly used on modern livestock farms.1 The benefits that anaerobic treatment of animal
wastes can bring to livestock producers, such as energy generation and waste stabilization for
odor control, have been well demonstrated by previous research.2"5 The remaining challenge is
to develop cost-effective and easily adaptable anaerobic reactor systems for farm applications.
Conventional anaerobic processes used for animal waste treatment are continuously stirred
tank reactors (CSTR) and plug-flow reactors. These processes are suited for treating concentrated waste such as the animal waste collected by mechanical scrapers, but not economical for
treating diluted liquid waste, such as the waste collected by flushing systems which are more
popularly used for large and new farms. Efficient anaerobic reactors for treating dilute wastewaters must retain biomass solids in the reactor with a short hydraulic retention time (HRT). The
Anaerobic Sequencing Batch Reactor (ASBR) has been under development at Iowa State University to meet this need6 and U.S. Patent No. 5,185,079 was issued for this technology. The
unique feature of the ASBR is its ability to grow and retain biomass with a long solids retention
time (SRT) through a natural selection process. It is simple to operate and requires low maintenance.
The studies on the ASBR for swine waste treatment have been conducted since 1990. Dague
and Pidaparti7 first tested the ASBR with swine waste at six volatile solids (VS) loading rates
ranging from 1.0 to 6.8 g/L/day, one HRT (6 day), and two temperatures (25°C and 35°C). The
ASBR proved to work satisfactorily. Schmit and Dague8 evaluated the ASBR at a lower temperature (20°C), three HRTs (6, 9, and 12 day), and different VS loading rates ranging from 0.9 to 5.0
g/L/day. Volatile solids reductions ranging from 40 to 60% were achieved. The study reported in
this chapter was carried out to further evaluate the ASBR for treating swine waste at short HRTs
(2, 3, and 6 day) at 25°C.
WORKING PRINCIPLES OF THE
ANAEROBIC SEQUENCING BATCH REACTOR
The ASBR is a suspended growth reactor which operates in a cyclic batch mode with four distinct phases per cycle. The four phases are feed, react, settle, and decant, as shown in Figure 1.
51st Purdue Industrial Waste Conference Proceedings, 1996, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
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