EXTENDED AERATION OF COKE-PLANT EFFLUENTS
J. Ganczarczyk, Professor
D. Elion, Project Engineer
Department of Civil Engineering
University of Toronto
Toronto, Canada M5S 1A4
INTRODUCTION
Activated sludge treatment of coke-plant effluents differs substantially from such
treatment of sewage and many industrial wastewaters because of concentration and
characteristic composition of these effluents.    Biological treatment plants for coke-plant
effluents are not very numerous but the technologies applied by these plants and their
operation patterns also differ   markedly.
The activated sludge treatment plant at Dominion Foundries and Steel Limited
(DOFASCO) in Hamilton, Ontario is the only Canadian plant and one of the few North
American plants for treatment of coke-plant effluents.    This plant is unique in its own
kind because it operated without any intentional removal of excess activated sludge.
During its history, the DOFASCO plant underwent few changes and in the year 1975
its aeration tank volume was doubled.    The characteristic performance of this plant
prior to this change and afterwards is the subject of this study.
WASTEWATER ORIGIN   AND GENERAL CHARACTERISTICS
The coke plant at the Dominion Foundries and Steel Limited (DOFASCO) in Hamilton, Ontario produced in 1975 an average of 3,680 t/day (3,340 kkg/day) of metallurgical coke from a low-sulfur West Virginia coal.      The following streams of wastewater
containing phenolics and thiocyanate were collected:    excess crude flushing liquor, condensate from the collection mains, condensate from primary coolers   and condensate
from the light oil plant.    The flow of these effluents ranged from 4,700 to  10,000
US gal per hr (17.8-37.9 m3/hr) and was a function of coal moisture contents and
connection of new wastewater streams to the system.     These effluents were originally
equalized in a storage tank of 425,000 US gal (1,609 m3) volume, which also provided
a separation of residual tar.
The next step of pretreatment (Figure 1) was ammonia stripping in a free-and-fixed-
leg Koppers still, installed in 1971.    The ammonia stripping was performed with lime
addition to raise pH over 9.5, and by addition of low pressure steam at a rate of
9,000-12,000 lb/hr (4,086-5,448 kg/hr), and high-pressure steam at the rate of 700-
1,000 lb/hr (318-454 kg/hr).    The additions of slaking water and steam condensates
provided a 30 to 40% dilution of the wastewater.    The wastewater discharged from the
still had temperature in the range of 210 F (99 C), and thus required cooling during
the summer through heat exchangers using bay water.   A 200,000 US gal (757 m3)
storage tank was provided upstream of the biological plant, allowing the wastewater
temperature to stabilize in the range of 150 F (65.5 C) and some suspended solids to
settle.   This wastewater was then biologically treated after being supplemented with
phosphoric acid at a rate of 1.3 US gal of 63% H3P04 per 100 lb phenolics (11 1/100
kg).
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