Dephenolization of industrial wastewaters catalyzed by polyphenol oxidase

Abstract

A new enzymatic method for the removal of phenols from industrial aqueous effluents has been developed. The method uses the enzyme polyphenol oxidase which oxidizes phenols to the corresponding o-quinones; the latter then undergo a nonenzymatic polymerization to form water-insoluble aggregates. Therefore, the enzyme in effect precipitates phenols from water. Polyphenol oxidase has been found to nearly completely dephenolize solutions of phenol in the concentration range from 0.01 to 1.0 g/L. The enzymatic treatment is effective over a wide range of pH and temperature; a crude preparation of polyphenol oxidase (mushroom extract) is as effective as a purified, commercially obtained version. In addition to phenol itself, polyphenol oxidase is capable of precipitating from water a number of substituted phenols (cresols, chlorophenols, naphthol, etc.). Also, even pollutants which are unreactive towards polyphenol oxidase can be enzymatically coprecipitated with phenol. The polyphenol oxidase treatment has been successfully used to dephenolize two different real industrial waste-water samples, from a plant producing triarylphosphates and from a coke plant. The advantage of the polyphenol oxidase dephenolization over the peroxidase-catalyzed one previously elaborated by the authors is that the former enzyme uses molecular oxygen instead of costly hydrogen peroxide (used by peroxidase) as an oxidant.

Phenol removal through combined biological and enzymatic treatments

“…Afterwards, the frozen cake was resuspended in distilled water and filtrated again to obtain enzymatic extract containing tyrosinase (Atlow et al, 1984). The activity of extracted tyrosinase was from 2,000 to 8,800 U.mL -1 , depending on the lot of mushrooms used.…”

Environmental applications of enzymes

“…Quinones are mostly unstable and undergo non-enzymatic polymerization to yield substances of low solubility (Atlow et al, 1984;Wada et al, 1993;Sun et al, 1992). Since a precipitate did not form spontaneously as in the case of peroxidases, Wada et al (1993) resorted to the use of chitin and chitosan to adsorb the reaction products formed.…”

Decolorization of phenolic effluents by soluble and immobilized phenol oxidases

“…Controls, to measure any sorption of colour by alginate beads per se, contained denatured enzyme. After treatment effluent solutions were centrifuged (20000 9, 10 min) to remove insoluble polyphenolics, adjusted to pH 7.6 (Atlow et al 1984) with 0.1 M phosphate buffer, and colour density measured at 465 nm. Optical density readings were converted to CU by the equation: CU=500 × A465/0.1~2 where 0.132 is the absorbance of 500 CU platinum-cobalt standard solution (Sundman et al 1981).…”

“…The use of tyrosinase was proposed as a cheaper alternative to HRP (Atlow et al 1984) as it uses molecular oxygen as the oxidant instead of hydrogen peroxide. A crude preparation of tyrosinase from mushrooms was as effective as highly purified commercial enzyme in dephenolizing water from a coke plant.…”