Treatment of combined and raw sewages with the dissolved air flotation process

In connexion with the development of a plant for dissolved-air flotation of storm-sewage overflows in a residential area of San Francisco, Calif., pilot-scale studies were carried out on the treatment of diluted sewage by this process, and experimental procedure and results are discussed. The experiments showed that dissolved-air flotation, with preliminary treatment with alum, is feasible for treatment of crude and combined sewages; the process is stable and can remove more than 90 per cent of the suspended solids in the influent. The advantages of this process over sedimentation are indicated.