1. It has been established that NChK is poorly oxidized by biochemical reactions, and negatively affects the biological purification of waste water. 2. The limiting admissible NChK concentration for the biochemical purification of ELOU waste water was determined by experiments in laboratory aerotankmixers. 3. The high NChK doses, as are used in the treatment of crude Arlan type oils of high sulfur content, complicate the methods of completely purifying the waste water emulsions, since considerable amounts of NChK (up to 15 g/liter) are accumulated in the waste water. Owing to this and the high content of mineral salts, it is necessary to dilute the waste water to bring the NChK content down to 200 mg/liter, and the content of mineral salts to 10 g/liter. The dilution of ELOU waste water must be done with domestic-fecal sewage, or with conventional pure water if the waste water is admixed with sewage from industrial plants that contains fairly oxidizing organic compounds. 4. Since NChK negatively affects the biochemical purification, it is indispensable in the very near future to search for deemulsifiers that can be used in the treatment of crude oils of high sulfur content, and be oxidized more efficiently by biochemical processes.