The application of crossflow microfiltration for the treatment of industrial wastewaters containing toxic heavy metals is described and the performance quantified and compared with technologies which are traditionally used for the treatment of such wastewaters. Case histories of the treatment of wastewaters generated from the metal plating industry and a battery recycling plant are given together with the operational performance of the full scale crossflow microfiltration plants which were subsequently installed. Metals of particular interest are cadmium, mercury and chromium where removals down to the ppb range are currently being requested. Heavy metal bearing effluents have traditionally been treated by the adjustment of the pH with lime or caustic soda to precipitate hydrated metal oxides. Sometimes a sulphide compound or other materials are added which cause the production of heavy metal compounds with lower solubility products. Removal of the heavy metal precipitate is then usually accomplished by settlement, occasionally followed by sand filtration [1]. With the advent of more stringent environmental legislation regarding the quality of the final disposal stream, the use of crossflow microfiltration is becoming an attractive alternative to the more conventional methods of treatment. The performance of settling tanks, settling tanks in conjunction with sand filters and a crossflow microfiltration system was assessed by pilot trials on a mixed plating effluent. The tests were carried out by Cory Environmental at their West Thurrock treatment plant in London. This plant is a toxic waste plant which receives and treats industrial wastewaters from UK industries. Tests were also carried out at a lead-acid battery breaking, lead recovery and refining plant, the waste water from this plant required treatment before disposal into the River Thames. The crossflow microfiltration system is based upon the concept of using a dynamic membrane to form the filtration medium. This membrane is laid down on the internal wall of a woven fabric cloth and may be formed by either the solids naturally present in the feed suspension or by the deposition of materials such as diatomaceous earth, metal hydroxides or kaolin. In this application the heavy metal precipitate provides a suitable membrane without the introduction of filter aids.