Random disposal of olive mill wastewater (OMW) creates environmental and health problems in the West Bank, as in all Mediterranean countries. More than 209 Olive mills currently operate in the West Bank, producing more than 200,000 m3 of olive mill wastewater between about November and January each year. OMW is highly polluting, with high concentrations of organic materials (COD = 80-200 g/l; BOD = 50-100 g/l) and phenolic compounds (Total phenol = 10 g/l). The extremely high organic loading and the phenolic compound concentrations pose a major pollution problem. The problem of the phenolic compounds increases when these compounds are oxidized during storage to form complex polyphenolic compounds, which are dark in colour and difficult to degrade. Experimental work has been carried out to understand the behaviour of OMW in relation to storage conditions, and to determine the factors that affect the oxidation of phenolic compounds.