552 



NATURE 



[February 22, i 



The Otto ozoniser consists of a series of transverse 

 plates, so arranged that a dielectric plate is placed 

 between the electrodes. The air is drawn or blown 

 between the plates, the silent discharge passing 

 between the spaces of the plates and thus ozonising 

 the air. Fig. 3 shows diagrammatically the manner 

 in which the air passes through the apparatus. An 

 alternating current at 6500 volts is employed. In 

 another form of the Otto ozoniser there is a metal 

 chamber, the walls of which make one electrode. 

 Within this chamber a number of sheet steel rings 

 are mounted on an axle, the edges of the rings being 

 sharpened. When in operation this bunch of rings 

 is rotated and forms the other electrode. No di- 

 electric is used. Air is blown through the box, the 

 rotation of the central electrode causing thorough 

 mixing. If an arc is struck it is immediately extin- 

 guished, as the electrode rotates because each of the 

 rings has a groove cut in it. The tension of the 

 current employed is about 25,000 volts. 



The providing of a pure water supply to our towns, 

 cities, and villages is of the very highest importance. 



Fig. a. 



In some cases where the water comes from sources 

 in which contamination of the supply is out of ques- 

 tion, such as from mountain lakes or from deep 

 springs, then no special purification is necessary. In 

 other cases, however, where the source of water 

 admits of, or even invites, contamination, purification 

 in some way or other is a sine qua twti. The method 

 chiefly employed is mechanical filtration. Chemical 

 methods, such as treatment with oxidising agents, 

 can only be carried out on a small scale. The sand 

 filtration method is partly bacterial and partly one of 

 filtration. The surface of the sand becomes coated 

 with a slimy deposit which is partly of bacterial forma- 

 tion ; consequently the water first passes through the 

 bacterial layer which exerts a beneficial effect in 

 destroying harmful bacteria, and also makes a much 

 finer filter than can be produced by the more or less 

 coarse-grained sand, and then it percolates through 

 the sand. Sometimes, however, owing to floods and 

 special contamination, the filter-bed breaks down, and 

 then it may be a very serious matter for the populace. 

 Therefore where there is a possibility' of water at any 

 time being contaminated, purification by some other 

 means is advisable. 



In the Ozonair process, which is being used in this 



NO. 2208, VOL. 88] 



country, the ozonisation of water takes places in th 

 stages — that is to say, the same water comes i; 

 contact with (j/one three times. In the first place, 

 water is atomised in presence of ozonised air, and 

 minutely divided particles of water then fall upon 

 upper part of a pile of glass spheres, or other sci 

 bmg arrangement, packed in a tower. As the w. 

 percolates down it meets an ascending stream 

 ozonised air. At the bottom of the tower it falls i 

 a tank through which ozonised air is blown by m» 

 of nozzles beneath the surface of the water in 

 tank. The tank is in the shape of an inverted c< 

 and a syphon is carried to the bottom of the ( 

 for carrying off the water. Owing to this arrai 

 ment, all the water gets equally acted upon bf r 

 being carried away. The syphon discharges the w. 

 on to steps, so that it cascades down into the stor 

 tank. As it cascades the water comes into con 

 with the atmosphere, and the excess of ozone i 

 up. Fig. 4, which is self-explanatory-, shows ■ 

 matically the arrangement of the plant. Shouiu 

 ozoniser get out of order or cease to work, the w 

 supply is automatically cut off. 



The Siemens-Halske system is largely employed 

 the Continent, the largest plant erected by them b< 

 at St. Petersburg. In this plant the method of st 

 lisation is slightly different from that previoi 

 employed. The water is conveyed into an emulsifv 

 tower by means of special injectors, the ozonised 

 being used to force the water into the bottom of 





•••>'•>'"">> -r-r-. 



Fig. 3. 



tower. The water and ozone therefore enter togetiv 

 and consequently very complete emulsifying takes 

 place. The water flows over from the top of the 

 tower, and is cascaded down to the reservoir. In this 

 particular case the water of the Neva is the source of 

 supply. It is very turbid, and is therefore previously 

 treated with 30 to 40 grams of aluminium sulphate 

 per cubic metre of water, and after settling for two 

 hours it is filtered. The water in the first place con- 

 tains a large amount of pathogenic and harmful b 

 teria, but after ozonising these have all disappear 

 In all probability a considerable number are remove© 

 by the precipitation treatment, because when water fl 

 softened by means of lime or other precipitant it f§ 

 always found to contain less bacteria than before 

 treatment. But, of course, precipitation could not 

 entirely be depended upon for sterilising purposes. 

 On the other hand, ozone can be depended 

 upon to sterilise. The St. Petersburg plant i$ 

 capable of dealing with 2000 cubic metres of 

 water per hour. There are three 150-h.p. steanr 

 engines for motive power, one, however, being always 

 held in reserve. The whole output of the engines ii 

 not required for working the ozonisers, as the powOT 

 is also used to operate the pumping and filtering" 

 plant and all the other necessary mechanical applir 

 ances. The ozonisers are worked with a three-phase 

 alternating current at 7000 volts and 500 periods. 



Other places on the Continent where ozone is used 

 for sterilising the public water supply are Paderborn, tl 

 Wiesbaden, Paris, Hermannstadt, Florence. N'ir 

 Chartres, Villefranche, Rovigo, and Chemnitz. T 



