Olive mill wastewater (OMW) originating from a two-phase olive oil producing plant was treated with a crude polyphenol oxidase (PPO) homogenate, prepared from potato waste peels. The treatments carried out were based on a 23-full-factorial, central composite design (CCD) in order to identify optimal operational conditions with regard to polyethylene glycol (PEG) concentration, pH, and treatment duration. The treatment performance was assessed by estimating the % reduction in total polyphenol (TP) concentration. The model obtained produced a satisfactory fitting of the data ( , ). The utilisation of the predictive model enabled the theoretical calculation of the optimal set of conditions, which were , ？h, and [PEG] = 900？mg L？1. Under these conditions, the optimal theoretical % removal calculated was . Examination of the treated samples with high-performance liquid chromatography (HPLC) showed that the potato homogenate afforded changes in the polyphenolic profile. Based on the experimental evidence, oxidation pathways were proposed. 1. Introduction Olive mill wastewater (OMW) is a highly polluting effluent of olive oil production and its disposal is a serious environmental peril. The main negative effect associated with its dumping is the high toxicity to plants, microorganisms, and aquatic organisms [1]. Thus, OMW is not appropriate for watering and fertilizing purposes and it is recalcitrant to biodegradation by bacteria and fungi. The toxicity of OMW is largely attributed to its exceptionally high polyphenolic burden, which may reach up to 80？g？L？1. This lends OMW a COD/BOD5 ratio of 2.5–5, which makes it 5–80 times stronger pollutant than domestic sewage [1]. The remediation of OMW has been a subject of several studies, dealing with catalysis-based oxygenation with various inorganic catalysts [2] and biological treatment, mainly with laccase- or peroxidase-producing fungi [3–7]. The use of enzymes in bioremediation processes has gained a wide acceptance because of the recognition that enzymes from various plant and microbial sources have several advantages over conventional physical and chemical treatments. These advantages include selective removal of particular pollutants, application to xenobiotic recalcitrant compounds, high reaction rates, operation over a wide range of pH and salinity, reduction in sludge volume, and simplicity of controlling the process [8, 9]. Among the enzymatic processes for waste treatment, peroxidase- and polyphenol oxidase-catalysed treatments of phenols are probably the most comprehensively studied [10]. Plant food
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