The Sterilisation of Water and Sewage Effluents, by H. C. H. SHENTON, F.S.E., M.I.Mun.E. (Member)
Journal of the Royal Sanitary Institute
THE sterilisation of water and of sewage effluents is a matter upon T which a great deal of fresh information has come to hand during the past year. In this country the results of work at Cambridge, Shrewsbury, and other places have been recently made known, while a number of works of considerable magnitude in America and Canada are proof of the usefulness and satisfactory working of sterilisation processes applied to waterworks and to sewage works belonging to large cities. There is some
... ence of opinion among chemists and bacteriologists as to the method of application of a sterilisillg agent, especially in the case of hypochlorite of lime, and the author would urge the necessity of settling whether the sterilising agent should be added before or after the organic matters have been filtered or settled from the water. The author suggests that sterilisation should be limited to the removal of harmful organisms, that the removal of organic matters should be effected by other means, and that in no way should sterilisation be allowed to take the place of the preliminary processes. It is, however, clear, on the other hand, that if the preliminary processes are used for the physical and chemical purification of the water only, and do not have to deal with bacteria, they may be worked at an increased rate, and consequently their area or extent may be reduced. A sand filter, for instance, may deal with the organic matters in suspension satisfactorily, but may fail to remove the bacteria satisfactorily till a thick scum has formed on its surface, causing a very slow rate of filtration. The size of the filter has to be in proportion to the slow rate of the flow. There appears to be excellent authority for saying that the proportion of chlorine required to remove the harmful organisms from water or from sewage effluent is very small, provided that the water is free from organic matter. Thus, Prof. Sims Woodhead demonstrated at Cambridge that one part of available chlorine in seven millions was sufficient to remove the coli from well water. Dr. Rideal, at the same meeting, pointed out that at Shrewsburv, where the water was treated by coagulation and filtration before sterilisation, '5 part of available chlorine per million was suflicient. This should be compared with the results obtained by Dr. Rideal at Hornsea, Yorks, where, presumably, the matters in suspension were not removed beforehand, at any rate to the same extent as at Shrewsbury, where from 1 to 2 parts per million of chlorine were required to remove the coli.