Reduction of phenol content and toxicity in olive oil mill waste waters with the ligninolytic fungus Pleurotus ostratus

Olive oil mill waste waters (OMW) constitute a major environmental problem because of the large amount produced and the toxicity of the phenolic compounds present. Several of these aromatic compounds can be assimilated to many of the components of lignin. Only few microorganisms, mainly “white-rot” basidiomycete, are able to degrade lignin by means of oxidative reactions catalysed by phenol oxidases and peroxidases. Both the low degree of specificity which characterizes these enzymes, and the structural relationships of many aromatic pollutants with the natural substrates of the enzymes, have suggested the use of ligninolytic organisms and of their enzymes for the treatment of these kinds of substrates. This paper investigates the ability of the “white-rot” basidiomycete Pleurotus ostreatus and particularly of the phenol oxidases it produces in the detoxification of OMW phenol compounds. Treatment of OMW with purified phenol oxidase showed a significant reduction of phenolic content, but no decrease of its toxicity was observed when tested on Bacillus cereus. Otherwise, the effect of processing OMW with the entire microorganism resulted in a noticeable detoxification of the waste with concomitant abatement of the phenol content.