MODERN METHODS OF WATER PURIFICATION. 



By D. M. ToMORY, M.B., CM., D.P.H. 



During- a recent absence on leave I was privileged to be able 

 to see the working of some of the finest sand filters in the 

 world in England, Scotland, Holland, Germany, and the 

 United States (especially the work of the Massachusetts State 

 Board of Health, whose contributions to knowledge of sand 

 filters is epoch-making); also " mechanical " filters, and '* pres- 

 sure " filters, as they are called, of various makes and systems, 

 and to see them worked with and without chemical addition 

 to assist in removing impurities. 



I took with me analyses of our Modder River water in order 

 to try to find a water which was more or less similar to ours, 

 and looked for a ;similarity in muddiness and difificulty in 

 settling", which is characteristic of our water — a water at the 

 same time turbid, discoloured, and liable to dangerous pollu- 

 tion, because the problem which interests Bloemfontein, and 

 therefore concerned me, was not merely removing" a colour or 

 turbidity as such, but also removing" the dangerous pollution 

 which I believe in our water accompanies and is indicated by 

 the turbidity. It is known how obstinately the Modder River 

 water refuses to settle clear, and how, where microscopical 

 clay particles are getting through the filters, germs will get 

 through also. That was for years Bloemfontein's trouble 

 both with the water from Sauna's Post and. after 1904, with 

 that also from Mazel's Poort, when that supply came into 

 service. But, small as microscopical clay particles are, there 

 is a still finer division of clay particles in our water, which could 

 be called sub-microscopical, and it is that svispended colloid 

 clay in extremely fine division that made our water so unsatis- 

 factory, clogged filters, and caused them to function so badly, 

 that the water supply was frequently dangerous and always 

 liable to suspicion. I had read of the success with which 

 similar difficulties were being overcome in the Uunited States 

 with such waters, and in 1905 wrote to the U.S. Government 

 Bureau concerned with the researches : they were good 

 enough, with that liberality in supplying" literature which is 

 available, that characterises the U.S. departments, to send 

 me various publications dealing with this question of chemical 

 assistance in treating waters otherwise incapable of satisfac- 

 tory purification. 



There was a groping towards the light during some time 

 after, until in 1906. in the winter months the water became so 

 bad that I suggested the use of alum or ferric-alumina to 

 precipitate the water, or the use of the special ashband pro- 

 <:ess, both used with success on the River Plate in South 

 America: at the same time, and quite' independently, Mr. 



