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The sewage of the chemical industry is generally a blend of clean (cooling water), and polluted water. The first recommendation is to separate the effluents, and to send clean water directly to the stream. Polluted sewage comes from the general services and from the individual fabrication plants. All the pollutions, which are dangerous for safety, able to dirty or destroy the sewers, or render more difficult or more expensive the final treatment, will be treated at the source. The sewage is treated at the general station, taking into account (i) toxins (ii) BOD (iii) COD and (iv) suspended material, and from the stream to which purified sewage is sent. In all cases a flocculation-settling will be necessary, the treatment being eventually completed by a biological step. Some tens of years ago, when a manufacturer intended to build an organic chemical plant, he chose, as far as possible, a place with a generous source of water, preferably a subterranean sheet or close to a sufficiently large flow stream able to receive its effluents. The circumstances have changed, the industries have expanded, the water sheets are no more sufficient, and the pollutions exceed the amount which can be accepted by the rivers. In those conditions, the plant such as I roughly described it, belongs to the past, and the manufacturer is, at present, faced with two problems: water supply and sewage.

Measures against water pollution in the production of organic chemicals from sources other than petroleum