A method of treating industrial wastewaters is provided. Specifically, the wastewater includes one or more organic contaminant materials and is pre-treated prior to filtering by the following steps The pH of the wastewater is adjusted to a pH in the range of about 2 to 6, and a combination of iron salts and peroxide are added to the wastewater and allowed to react for a period of at least about three minutes. Next, the pH of the wastewater is adjusted upwards to a value of at least 7 and precipitating or flocculating agents are added to form an insoluble contaminant bearing compound. The compound is then filtered from the wastewater thereby removing the contaminant materials from the wastewater. This invention is particularly suited for use with single pass flow-through filters, and most particularly suitable for high flow rate single pass flow-through filters. The method of the present invention results in minimization of filter clogging and maintenance of high filtration flow rates, with reduced need for cleaning cycles using lengthy treatment by acid based or detergent mixtures.