INFLUENCE OF ORGANIC SHOCK LOADS ON THE
PERFORMANCE OF AN ANAEROBIC FLUIDIZED BED SYSTEM
David Barnes, Assistant Professor
Peter J. Bliss, Senior Lecturer
Bruce Grauer, Student
Eugene M. Kuo, Student
Karen Robins, Student
School of Civil Engineering
University of New South Wales
Kensington, 2033
Australia
Greg Maclean, Manager
Austgen-Biojet International Pty Ltd.
Chatswood, Sydney
Australia
INTRODUCTION
The fluidized bed reactor has been developed as a compact wastewater treatment system. The process relies upon passing a flow of wastewater up through a bed of media on which is grown a biomass.
The upflow of the wastewater is sufficient to separate the particles of media/biomass and hence fluid-
ize the bed. The first reports of this type of application of expanded and fluidized beds to treat wastewater, described aerobic and anoxic systems [1,2]. More recently anaerobic systems have been
reported [3-6].
The anaerobic fluidized bed is one of several anaerobic systems which use anaerobic micro-organisms in an efficiently engineered process. Anaerobic reactions have several major advantages when
compared with aerobic reactions. The anaerobic processes generated methane which can have some
value as a fuel and, partly because the end products are mainly gaseous, the yield of sludge is low.
Anaerobic process sludge yields of 0.1-0.2 kg/kg BOD are reported [5,7], while for aerobic processes
sludge yields of 0.5-1.5 kg/kg BOD have been recorded [8,9]. However, these merits have not been
fully realized in the traditional anaerobic municipal sludge digester. In many cases long hydraulic
retention times (15-25 days) have been required for sludge digestion [7]. Consequently the units are
large and in many cases there is inadequate mixing [10] which reduces the efficiency of the digesters.
High rate anaerobic processes in reactors engineered to provide a high concentration of viable biomass use an upflow of wastewater to provide adequate mixing. The upflow sludge blanket [11] passes
the wastewater through a bed of sludge at a relatively low flow rate but achieves treatment with low
recycle rates. Optimum operation of the upflow sludge blanket processes is reported when the biomass
forms granulated sludge which has a high activity and can be easily retained in the reactor. In
expanded or fluidized beds the biomass grows on an inert solid media such as sand or activated carbon
[ 1 -6] of small size and high surface area. The upflow of the wastewater is balanced by the mass of the
media/biomass and a stable expanded or fluidized bed can be established.
In Australia standards for discharge to sewers are set by the regional authority responsible for the
municipal wastewater treatment and discharge to surface waters is regulated by a State Environmental
Authority. Because the anaerobic fluidized bed (AFB) process is capable of high BOD removals with
little sludge production, the process can be used to reduce the pollutional load prior to aerobic polishing or prior to sewer discharge. For sewer discharge the BOD and suspended solids should normally
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