Report of the Medical Officer of Health / Municipality of Colombo.
- Colombo (Sri Lanka). Public Health Department
- Date:
- [1928]
Licence: Public Domain Mark
Credit: Report of the Medical Officer of Health / Municipality of Colombo. Source: Wellcome Collection.
115/142 page 74
![for a period long enough to ensure the death of all, or nearly all, the enteric germs which may perchance pass into the works, slow sand or rapid mechanicai filtration, followed, since 111] (I by chlorination. In the case of the Labugama supply storage is very unequal in its effects and the filters, though they must greatly diminish the number of disease producing organisms, cannot eliminate them altogether even when working under ideal conditions ; after filtration the organism will still be present but in a larger volume of water. A bacillary infection of the enteric type differs from a protozoal, such as that due to Entamoeba histolytica, in one important respect. If even a few stray living B lyphosns arrive at Colombo and gain access to a nutrient medium, such as milk, they may start to multiply and the consumption of the milk may originate an outbreak of enteric fever. The amoebae also may excyst and pass through their various stages of development outside the body but only in very special sorts of culture media under specially favourable conditions unlikely to be met with in practice, for instance the medium must be kept at or near blood heat. In practice, therefore, the occasional access of a few E. histolytica cysts to a water supply is less dangerous than a correspond¬ ing degree of infection with B. typhosus. Moreover, the one infection can be controlled by the appropriate treatment with such drugs as emetine hydrochloride, stovarsol, and yatren, and when so treated the mortality from amcebiasis is negligible, whereas the clinical course of enteric cannot be modified with any degree of certainty by any therapeutic measures at present known. The mortality of enteric due to B. typhosus, if unmodified by anti-enteric inoculation, may be as high as 30 per cent. The dose of chlorine required would depend on the state of the water. Suspended matter absorbs chlorine. No disinfectant action is obtained till the affinity for chlorine of the organic matter in solution or in suspension has been satisfied. Hence it would be more economical to apply the chlorine to the filtered water. It should be thoroughly mixed with the water in the clear water basin. There is ample time for the chlorine to exert its full disinfection action before reaching the consumer. The dose required would probably vary from about 0'2 to 0'5 parts per million and the cost would be about Rs. 40 per diem at the present price of chlorine. The cost of an installation capable of delivering 80 lb. of liquid chlorine per diem more than twice what would usually be necessary, would be under Rs. 24,000. As regards taste troubles a great deal more is now known about the subject than in the early days of chlorination. Reference may be made to the reports of Sir Alexander Houston issued by the Metropolitan Water Board for details of the superchlorination, permanganate and ammonia methods which have been successfully employed in London and elsewhere. See also the paper read by Howard and Thompson at the 45th Annual Convention of the New England Water¬ works Association which is summarized in Sir Alexander Houston’s 21st Annual Report and the abstract of the article by Adamson the iodoform taste acquired by chlorinated water in the l'Jth Annual Report. Adams showed that such tastes are di\e to be absorbtion of minute traces of pheneloid bodies from the atmosphere and their interaction with chlorine. The Labugama Reservoir Water and its Treatment. On a clear sunny day in the dry weather an observer in a boat in the bay at the far end of the lake looking down into the water discharged by the main stream will see a deposit of black silt at the bottom and on its surface twigs and leaves in every stage of disintegration into mould. The remains of millions of leaves lie there. Bubbles of marsh gas (methane) continually arise and break upon the surface. A similar process must be taking place on a smaller scale at the mouth of many streams entering the reservoir. The Waterworks Engineer proposes to place hakes or silt traps at the mouth of each large stream and, if possible, to dredge the long standing deposit of organic matter at the mouth of the main stream. This should bring about a definite decrease in the organic matter in solution in the water as a whole and in the number of microbes it is able to support. Silt also accumulates at the deep end of the lake opposite the straining shaft, but large quantities of this can readily be scoured out, whenever surplus water is available, by opening the bottom sluice. Let the variations in the quality of the water passing into the supply be now considered. In the first instance suppose the weather has been dry for the preceding month and the level of the water about three feet above the thirteen foot sluice. Under these conditions the water passing into consumption will be of the highest quality. Lactose fermenters of the true faecal type will probably be absent from 100 c.c. The count on ordinary agar may be less than one per cubic centimeter. Chemically the water will be exceptionally pure and well oxygenated and physically it will be clear, odourless, and tasteless. In fact the ideal water that has given the Colombo supply its great reputation. Now let the sky darken and a cyclone appear on the scene. Torrential rains descend upon the watershed, raising the water level by many feet within twelve hours, and sweeping immense quantities of organic debris into the lake. A great change in the water soon takes place; it becomes turbid and develops a slight taste of iron, the albuminoid ammonia figure goes up, ammonia and even nitrites may appear, the bacterial count rapidly rises and true faecal lactose fermenters appear in volumes as small as 1/10 of a c.c. or even less. In short the water becomes bad as judged by any arbitrary official standard. Now let the rain cease and the sun once more appear. The complex bio-cliemical and physical processes known as self-purification at once begin. The suspended matter sinks. As transparency increases at the surface levels the rays of the sun, the most potent force in nature, commence to exert their tremendous disinfecting and photo-synthetic power. Algae, protozoa, and numerous bacteria attack the organic matter brought in by the storm and break it down towards the inorganic state, taking up much dissolved oxygen in the process, which is continuously renewed from the surface of the water. Before very long the water is restored to all appearances to its original purity.](https://iiif.wellcomecollection.org/image/b31495278_0115.jp2/full/800%2C/0/default.jpg)
