25    A STUDY OF ANAEROBIC SEQUENCING BATCH
REACTORS FOR THE TREATMENT OF SOLUBLE
WASTES
W. A. Sanchez, Consultant
K. Kennedy, Research Officer
Division of Biological Sciences
National Research Council of Canada
Ottawa, Canada K1A OR6
M. F. Hamoda, Professor
Department of Civil Engineering
Kuwait University
Kuwait
R. L. Droste, Associate Professor
Department of Civil Engineering
University of Ottawa
Ottawa, Canada KIN 6N5
INTRODUCTION
Sequencing batch reactors (SBRs) are fill-and-draw periodic systems which are successfully being
used in activated sludge treatment. As described by Arora et al.} SBR technology is not new and in
fact preceded the use of continuous-flow activated sludge technology. However, SBRs were forgotten
for over half a century and were only revived in the early 1970s by the work of Irvine and Davis.2 The
basic characteristics of single and multiple-tank SBR systems are described by Irvine and Busch.3 The
single tank system is well suited for non-continuous flow situations, such as those that occur in the
food-processing industry or in small rural towns. Multiple-tank systems are applicable for constant or
variable continuous flows.
To date, SBR technology has been applied only to aerobic biological processes. For these, the
advantages of SBR over continuous-flow systems cited in the literature include operational flexibility,
flow equalization, near-ideal settling, simple operation and compact layout of system.
Reports on the intermittent operation of anaerobic processes are scarce and limited in scope.
Asinari di San Marzano et al} examined the effect of semi-continuous loadings on reactor performance. Laboratory scale experiments were conducted with anaerobic digesters treating paunch and
bovine manure. The following waste loadings were tested: biweekly loadings for hydraulic retention
times (HRT) of 20 days; 3 times a week for HRTs between 12 and 17 days; and, once a day, 5 days a
week for HRTs below 10 days. The authors concluded that semi-continuous loadings appeared more
reliable than continuous loadings but recommended that no more than 20% of the digestion mixed
liquor be replaced at any one time. Farrell et al} investigated the effects on microbial densities and
other process parameters of changing the feeding protocol of anaerobic digesters from "draw down,
then fill" (D/F) to "fill, then draw down" (F/D). They did not observe any significant effect on
volatile solids or COD reductions. They, however, noted that a D/F feeding protocol resulted in
improved reductions of viruses and bacterial fecal indicators in digester effluents. A mathematical
analysis comparing treatment efficiencies and kinetics between sequencing batch and complete mixed
systems has been presented by Droste.6 The use of anaerobic SBRs for the treatment of coal conversion wastewaters has been proposed7 but only limited data have been reported so far.
The application of SBR technology to anaerobic treatment is of interest due to its inherent operational flexibility. Important potential advantages of SBRs that merit investigation include:
• ability of process to handle periodic flows;
• possibility of taking tanks on and off-line to meet either short-term or seasonal variations;
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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