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Waipa Post, Volume 51, Issue 3645, 19 July 1935, Page 4

is still held practically unoxidised in the sludge. The second stage embraces the bacterial oxidation of the nitrogenous matter in the sludge, the process being accelerated by the very efficifjkt _ agitation. This process is both bn-* logical and colloidal. When the action is complete—consideringr one particular case—-the treated sewage is run into sotting tanks, where the sludge, being thoroughly flocculated, is quickly deposited, and in one hour settlement is complete. The effluent, which is now perfectly clear and free from collodial polluting material, is drawn off and utilised or disposed of as desired. In semi-arid districts in America it is used in locomotive boilers, for irrigation, for washing motor cars and so forth. ESSENTIAL PROCEDURE. The sludge left behind is ordourless and inoffensive. Being “activated,” or rich in the necessary bacteria, seme of it is used to “seed” the next batch of incoming sewage. This procedure is essential to the whole process, and it was this discovery th a t led to the present development, and to the term Activated Sludge Process. The Avhole of the humus and the greater part of the nitrogen is concentrated in the sludge, which, bearing in mind its inoffensive nature, makes a particularly valuable manure. Generally speaking, best results are obtained by Using it in conjunction with an artificial fertiliser, which steps up its nitrogen value. This is the process of sewage treatment which must ultimately come into general use all over the world. Plants are operating, or are being constructed at Manchester—where the process originated Birmingham, London, Chicago, New York, Milwaukee, Bombay, Shanghai and a host of other cities.