42    FEASIBILITY OF SYNCHRONOUS
AEROBIC/ANAEROBIC PROCESSES WITH A SINGLE
UPFLOW SLUDGE BED SYSTEM
C.F. Shen, Research Associate
D. Rousselle, Summer Student
S.R. Guiot, Project Leader
Biotechnology Research Institute
National Research Council Canada
Montreal, Quebec, Canada, H4P 2R2
INTRODUCTION
Many xenobiotic compounds which are refractory under aerobic conditions' seem to be readily
biotranstormed anaerobically. In turn, partially degraded products which resist further anaerobic
degradation can be completely mineralized by aerobic microorganisms.2 These facts point out
the limitation and complementary aspects of aerobic and anaerobic treatments, and suggest thar
compounds degrading through a series of reductive and oxidative steps may be most efficiently
biodegraded by sequential anaerobic-aerobic processes in which anaerobic digestion is a primary
treatment to furnish partially or completely degraded compounds for aerobic polishing.3 In an
anaerobic-aerobic sequence system, the anaerobic and aerobic bacteria function in separate units
that complement each other. The economical scheme of operating full-scale anaerobic-aerobic
systems is to construct engineered microecosystems integrating oxic and anaerobic niches and
creating synergism between oxidation and reductive catabolisms. The co-existence of anaerobes
and aerobes in oxic4 and anaerobic5 environments indicates the possibility of constructing micro-
ecosystems in which both anaerobes and aerobes are able to survive. Under 02-limited conditions, aerobic respiring microorganisms can maintain very low dissolved oxygen concentrations
in the aerobic/anaerobic co-cultured system, and the complete inhibition of anaerobes is avoided.
Even in the aerobic process, the oxygen consumption of the aerobic bacteria on the periphery of
immobilized biofilm can result in a built-up of an oxygen gradient,1 leaving the inner layer of
biofilm free of oxygen and preventing the toxicity of 62. Anaerobic granular sludge is an appropriate matrix for the development of the above microecosystems including oxic and anaerobic
niches.6 The facultative bacteria on the periphery, which create an abrupt oxygen gradient in the
sludge, could prevent 02-toxicity to the 02-sensitive Methanoseata-\ike methanogens located in
the core of the sludge.7 Obligatory anaerobic bacteria in the granular sludge have demonstrated
their surviving abilities when exposed to certain 02-limited conditions.6-8-9
Aerobic/anaerobic coupled bioprocess seems to have great potential in the complete biodegradation of a broad range of recalcitrant toxic compounds. However, much work remains to be
done before the aerobic/anaerobic coupled systems are employed to their full-scale application.
The knowledge of bacterial behavior in an aerobic/anaerobic coupled reactor is lacking; the operation and design of aerobic/anaerobic coupled bioreactors are still at a preliminary stage. An
understanding of the influence of process parameters, especially dissolved 02 concentration, on
the reactor performance and bacterial behavior will enable us to optimize the operating conditions and improve the reactor design.
50th Purdue Industrial Waste Conference Proceedings, 1995. Ann Arbor Press, Inc., Chelsea. Michigan 48118.
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