FATE OF BASIC POLLUTANTS IN TREATMENT OF
COKE-PLANT EFFLUENTS
J.J. Ganczarczyk, Professor
Department of Civil Engineering
University of Toronto
Toronto, Canada M5S 1A4
INTRODUCTION
Treatment effects of coke-plant effluents are usually evaluated in terms of removal of
only some characteristic pollutants like mono-hydric phenols, cyanide and ammonia.
Determination of other important components of this wastewater like thiocyanate and some
derivatives of polynuclear aromatic hydrocarbons is often neglected. Determinations of
wastewater composed characteristics like biochemical oxygen demand (BOD) chemical
oxygen demand (COD), dissolved solids, extractables, color, etc. are made only occasionally.
A justification for such an approach may be found in some respective analytical difficulties
and uncertainties, but the growing requirements for receiving water bodies demand much
broader control of the wastewater treatment.
In the scope of this work some new analytical information is presented on coke-plant
effluents treatment in laboratory, pUot-scale and full-scale, to support other avadable data
on the subject. On this basis, fate of specific wastewater chemical components and
composed characteristics is established for particular stages of the wastewater pre-treatment
and treatment [ 1 ]. Special attention is directed to formulate the characteristics effectiveness limits for particular treatment methods. This approach is considered to facUitate the
selection of treatment methods and treatment strategy for the specific treatment
requirements.
Table I presents a range of component concentrations characterizing typical coke-plant
effluents. This information is basically relevant for coke-plants generating more than 40
U.S. gallons of effluents per ton of coke (150 L/t). The majority of the studied coke plants
generate a wastewater flow of 50-100 U.S. gal/t of coke (190-380 L/t). Usually, this flow is
a function of the coal moisture contents and depends also on various additional wastewater
streams being connected to the excess of flushing liquor which constitutes the major
component of the wastewater. Coal sulfur and nitrogen contents as well as the cokeing
temperature affect the concentrations of majority of the chemical compounds constituting
these effluents.
Figure 1 shows a conventional flow-sheet of coke-plant effluents treatment. The indicated
treatment sequence is followed later in discussing fates of the particular pollutants.
TRANSFORMATIONS OF BASIC POLLUTANTS
Fate of Phenols and Phenolics
To simplify analytical procedures, phenols in this wastewater are often determined as
phenoUcs, the latter showing quite often misleadingly high concentrations.
Usual first step of phenol and phenolics removal is solvent extraction. Its results are
shown in Table II. This operation is preferential for cresols versus phenol (Table HI) and also
removes from wastewater piridine bases and neutral ods. The relatively smaU popularity of
solvent extraction for treatment of coke-plant effluents in North America is justified by a
low market value of the recovered material. However, an application of such treatment can
make the subsequent biological treatment less expensive and more efficient.
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