56    DISSOLVED OXYGEN CONTROL IN A COUPLED
FLUIDIZED BED SYSTEM
Richard M. Jones, Process Development Engineer
Henryk Melcer, Head
Biological Processes Section
Wastewater Technology Centre
Environment Canada
Burlington, Ontario L7R 4A6
INTRODUCTION
The Coupled Biological Fluidized Bed Process
The biological fluidized bed process is a modification of more conventional fixed film processes,
such as the trickling filter, in which wastewater is passed upward through a bed of granular support
medium, typically sand, at a sufficient velocity to expand or fluidize the medium. The granular
medium provides a large surface area for the establishment of a biological film. The fluidized bed
process was selected to investigate the treatment of coking plant wastewaters in view of the significant
advantages offered in terms of reduced reactor volumes that result from the high biomass concentration maintained on the support medium.W
The technical feasibility of treating coal distillation condensates was evaluated during a 3-year study
at Environment Canada's Wastewater Technology Centre (WTC). The feed to the pilot scale test
system consisted of effluent from fixed and free leg ammonia stills at the by-product coke plant of
Dofasco Inc. in Hamilton, Ontario. The pilot plant consisted of two fluidized bed reactors in series,
coupled to provide carbon oxidation, nitrification and denitrification in the predenitrification operating mode (Figure 1). The anoxic denitrification reactor was 115 mm in diameter and the oxygenic
nitrification reactor, 290 mm in diameter. The bed heights and reactor volumes were adjustable by
relocation of the position of the sand/biomass wasting valve.
The experimental objective of this research was to determine those operating conditions required to
maintain stable nitrification and complete denitrification under both steady state and dynamic operating conditions. Details regarding operating, sampling and analytic procedures have been presented
elsewhere.3'4 A specific operating problem existed relating to the control of the dissolved oxygen
concentration in the oxygenic fluidized bed reactor, the solution of which forms the basis of this
paper.
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Figure   1.    Coupled  pre-denitrification-nitrifi-
cation biological fluidized bed process.
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