AbstractTreatment of waste water from the metal‐working industry.Recent legislation has triggered a round of innovation in purification techniques for the treatment of waste water from the metal‐working industry. The historical development took place essentially in three generations, viz. flow‐through processes, recycling ion‐exchange units, and process oriented work‐up. The process engineering of process oriented work‐up is basically known with regard to the unit operations. Work performed during the last two years has focussed on transforming the known processing principles into plant engineering and accomplishing the step to the industrial scale plant, i.e. to bring it up to the present state