START-UP OF A FULL-SCALE NITRIFICATION-DENITRIFICATION
TREATME1MT PLANT FOR INDUSTRIAL WASTE
T. R. Bridle, Senior Development Engineer
D. C. Climenhage. Technical Supervisor
A. Stelzig, Senior Process Engineer
Dupont of Canada
Maitland, Ontario, Canada
INTRODUCTION
Dupont of Canada has been conducting a Research and Development Program to treat
BOD and nitrogen discharges in wastewater from its Maitland Works since 1969.
During that time a biological treatment process, patented in Canada with patent applications in nine other countries, has been developed, from laboratory through pilot plant-
scale [1,2] and finally the construction and start-up of a full-scale facility.   In this paper
we will report on the start-up and debugging of what we believe is the world's first full-
scale nitrification-denitrification plant designed to treat high-strength chemical plant waste.
During our early development a number of alternate treatment methods were studied.
These include:   standard incineration, fluidized bed incineration and high-temperature wet
oxidation.   Repeated evaluation during the development program indicated that biological
treatment offered the best efficiency for both nitrogen and carbon removal at the lowest
treatment cost.
After studying five biological treatment schemes a two-stage process was selected [3,4].
PROCESS DESCRIPTION
The biological treatment plant (Figure 1) consists of two stages: an anerobic mixed
basin followed by an extended aeration basin.   Solids separation and sludge return is
accomplished in a dissolved-air flotator unit and filter system.
•St Figure 1.  Schematic of waste treat-
-e
ment plant.
Wastewater, at a pH of between 3 and 8 and a flow of 3.0 mgd,enters the anaerobic
basin where it is mixed with recycle from the aerated basin, giving a hydraulic residence
time of 18 hr.   Here under anaerobic conditions complete denitrification occurs, with
the removal of about 20 to 30% of the organic carbon in the feed.   The pH of this basin
remains between 6.5 and 7.5 through the removal of NOx and acidic carbon in conjunction with a buffering effect of the recycle from the aerobic basin.
Denitrified waste overflows the anaerobic basin to the aerobic basin where the remainder of the organic carbon is removed together with nitrification of the ammonia
and organic nitrogen compounds.   Recycle of this material (up to 2x feed rate) to the
anaerobic basin allows for partial denitrification of the nitrified waste.   Further denitrification in the aerobic basin produces an effluent of < 10 mg/l NOx.   The hydraulic
residence time in the aerobic basin is 60 hr at our normal recycle rate of 1:1.   The composition of the wastewater, plus the process design, eliminates the need for addition of
alkalinity in this basin.   VSS levels in both basins are held between 2000 and 3000 mg/l.
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