54    REMOVAL OF PHENOLIC COMPOUNDS FROM
WASTEWATERS USING SOYBEAN PEROXIDASE
Harold Wright, Graduate Student
J.A. Nicell, Assistant Professor
Department of Civil Engineering and Applied Mechanics
McGill University
Montreal, Canada H3A 2K6
INTRODUCTION
Toxic and odiferous phenolic compounds are present in wastewaters generated by a variety of
industries including petroleum refining, plastics, resins, textiles, and iron and steel manufacturing among others. Conventional methods of phenol removal from wastewaters include bacterial
and chemical oxidation, GAC adsorption, steam distillation, and extraction. Peroxidase enzyme
catalyzed removal of phenolic compounds from wastewaters was first reported by Klibanov et al.
in 19801 and has since received much attention.
The enzymatic removal of phenolic compounds from wastewaters may be viewed as a three
step process. The first step involves the cycling of peroxidase enzyme through three enzyme
forms having oxidation states of +3, +5 and +4:4
In the peroxidase cycle, hydrogen peroxide (H202) oxidizes ferric (+3) peroxidase to a +5 oxidation state and two equivalents of phenolic compound (PhOH) reduce the oxidized enzyme back
to the ferric form in two one-electron steps. In the process of reducing the enzyme, the phenolic
compounds are transformed to phenolic free radicals (PhO*). In peroxidase literature, the +5 and
+4 oxidation states are commonly referred to as Compound 1 and Compound 2, respectively.
The second step of the phenol removal process involves the non-enzymatic reactions of phenolic free radicals. Free radicals will either combine with each other to form phenolic polymers5 or
they will undergo radical transfer with polymers already present to form polymer radicals:6
PhO* + PhO- -> Polymer
PhO* + Polymer -» PhOH + Polymer radical
Phenolic polymers may also partake in the peroxidase cycle and be converted to polymer radicals.5 Polymer radicals may react with other radicals to form larger polymers. The end result is a
solution containing polymers of various sizes.7 Since the phenolic polymers are less soluble than
their precursors, they precipitate out of solution. The physical removal of phenolic polymers
from solution by gravity settling or filtration, aided in some cases by coagulants, is the third and
last step of the overall phenol removal process.3
50th Purdue Industrial Waste Conference Proceedings, 1995. Ann Arbor Press, Inc.. Chelsea. Michigan 48118.
Printed in U.S.A.
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