AN OZONE REACTOR FOR COLOR REMOVAL
FROM PULP BLEACHERY WASTES
P. B. Melnyk, Assistant Professor
David Judkins, Graduate Student
Chemical Engineering Department
Case Institute of Technology
Cleveland, Ohio 44106
Aharon Netzer, Head
Physical Chemical Processes
Wastewater Technology Center
Canada Centre for Inland Waters
Burlington, Ontario, Canada
INTRODUCTION
Intensely colored industrial wastes do more than just deteriorate the aesthetic   appearance of a receiving stream.   These wastes inhibit the natural photosynthetic production
of oxygen by decreasing light penetration.   The net result can be an oxygen deficit.
These color pollutants also chelate metal ions, thus increasing the cost of water treatment and the likelihood of contamination by solubilizing heavy metals.   For these reasons,
the U.S. E.P.A. has proposed criteria for limiting the discharge of color wastes [ 1 ].
The treatment of color wastes is an important problem for the pulp and paper industry.
Effluents from the caustic pulp bleaching process are highly colored [2], and of significant
volume, i.e.,   18,000 gal/ton pulp [3].   The problem is further compounded because the
lignin compounds responsible for color are biologically refractive.   Thus, biological, i.e.,
secondary, treatment processes are not effective in removing color.   Chemical oxidation
with ozone has been shown to be very effective in reducing color, while not producing a
by-product which requires further processing [4].   This latter advantage is not shared by
other proposed methods of treatment [5].
The design of an ozone reactor along with estimates of capital and operating costs are
presented.   This design is based upon rate data for color removal and ozone consumption
as measured for a caustic bleachery waste at two temperatures (29.5 C and 60.5 C) and
two initial ozone concentrations (0.0106 and 0.0174 mole fractions).   The changes in
both chemical and biological oxygen demands which occur simultaneously with color
removal are also reported.
EXPERIMENTS
With the exception of the experimental reactor, and the analytical techniques used to
determine the ozone concentrations in the gas streams, the same experimental procedures
were followed as reported earlier [4],   Color was determined by the methodology recommended by the Pulp and Paper Research Institute [6] and reported in mg/1 of color units.
One color unit is equivalent to the absorbance at a wavelength of 465 nm by 1 mg/1 of
platinum in a standard chloroplatinate solution (Fisher Scientific Reagent No. So-P-120).
Oxidation by potassium dichromate was used to measure the chemical oxygen demand
[7] while continuous respirometry was used for the biological oxygen demand.   A special
purpose  UV adsorbance meter (Dasibi model 1003AH) monitored gaseous ozone concentrations.
The rate data was obtained from a continuous-flow reactor illustrated in Figure 1.
Pertinent information about the reactor geometry, and operating conditions is summarized
in a table located in the appendix.   The residence time distributions of both the liquid and
gaseous phases are well-mixed.   Thus, rates of color removal or ozone consumption can be
determined directly by substituting the inlet and outlet concentrations, and the residence
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