The Faipadajl Society is not responsible for opinioiis expressed before il b y Aufhors OY Spcakcrs. OF FOUNDED 1903. TO PROMOTE THE STUDY OF ELECTROCHEMISTRY, LLECTROMETALLURGY, CHEMICAL PHYSICS, METALLOGRAPHY, AND KINDRED 8UBdECTS. _ _ ~ _____ ~ - - _- - -______ ~ _ _ _ _ _ Vor,. IV. OCTOBER, 1908. PART 2. _ _ _ _ _ -- _ ~ _ _ _ _ _ _ _ _ _ _ _ ~ ______ ~ _ _ _ _ _ _ _ _ _ _ _ _ ~ - -~ .- T H E INDUSTRIAL USES OF OZONE, PARTICULARLY FOR THE PURIFICATION OF WATER. BY F. MOLLWO PERKIN, PH.D. ( A Pnpei read before the FaiTaday Society, Tuesday, May 12, 1908, Mr. LEON GASTER in the Chair.) The formation of ozone by the discharge of an electrical machine was originally noticed by Van Marum in 1785, but it was Schijnbein in 1840 who first actually prepared it and gave it the name “ozone,” from the Greek meaning “smell.” He also showed that it was much more active as an oxidising agent than ordinary oxygen.It is produced by the slow oxidation of phosphorus, and the peculiar smell of this element is really not the smell of phosphorus but the smell of ozone, and this can be shown to be the case by adding small quantities of substances to phosphorus which prevent its oxidation, when the smell is no longer perceptible. It also appears to be produced in small quantities by the burning of hydrocarbons. It is likewise formed in the open country, probably by slow evapora- tion or possibly by electronic action of the sun. Thus, where there are large quantities of water, as in the neighbourhood of the sea, the amount of ozone will probably be greater than in dry inland districts, although what is often at the seaside put down to the smell of ozone is simply the smell of decaying seaweed.It is formed in considerable quantities when fluorine acts upon water. If a drop of water is introduced into a tube filled with fluorine, reaction immediately ensues, and the tube becomes filled with deep blue vapour; this is ozone, which has a blue colour when concentrated- 3F, + 3H,O = 6HF + 0,. Ozone is also produced at the anode when acid solutions of water are electrolysed, particularly if the electrode is a platinum tube through which cold water is passed. Fischer and Massenez (2eit.f. anorg. Chem., 1907, 229) have obtained 25.27 per cent. of ozone in electrolytic oxygen by cooling to oo ; such a process would not however be satisfactory on a large scale.The best method to prepare it is to subject oxygen to the action of the silent electric VOL. IV. PART 2. T 682 THE INDUSTRIAL USES OF OZONE, PARTICULARLY discharge, the oxygen thereby receiving electrical energy and becoming converted into ozone, thus- 3 0 , + energy = 203. Consequently ozone is less stable than oxygen and is in a condition in which it will readily part with the energy originally received electrically in the form of heat--e.g., when the pure gas explodes or as chemical energy when it oxidises substances. The thermochemical equation accounts for its in- stability. 0, + 0 = 0, - 32,400 cal. Ozone is a blue gas-although when largely diluted with air this colour is not noticeable-which boils at -119"; it can therefore be obtained FIG.I. by passing ozonised oxygen through a tube surrounded by liquid oxygen (boiling point -1S2*5), a deep blue liquid being obtained. Its well-known sterilising properties are due to its great power of oxidation, and it is thus a very powerful bactericide. The employment of ozone or ozonised air for the purification of water on an industrial scale was suggested some years ago, but it is only within the last decade that the suggestion has been practically worked out and actually employed commercially.:: Of all the workers on the subject Messrs. Siemens and Halske have been most indefatigable and have fitted up works a t Paderborn and Wiesbaden, which have been in operation for some years and have given considerable satisfaction, particu- larly the former. The providing of a pure water supply to our towns, cities, and villages is of the very first importance.In some cases where the water comes from sources in which contamination of the supply is out of the question, such as from mountain lakes or from deep springs, no special purification is * Werner Siemens originally suggested its employment for this purpose in 1889, but the idea was put on one side, and not until 1898 was it again taken up by Messrs. Siemens and Halske.FIG. 2.FOR THE PURIFICATION OF WATER. 83 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 quZ non. The method chiefly employed is mechanical filtration. Chemical methods, such as treatment with oxidising agents, can onlj7 be carried out on a small scale.Electrolytic methods, although frequently tried and continually patented, have also proved not to be satisfactory, at any rate on a large 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 partially of bacterial formation ; 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 flo-ods and special contamination, the filter- bed system breaks down, and then it may be a very serious matter for the populace.FIG. 3.-Battery of Ozonisers. Purification by means of ozone may be said to be electrical, chemical, and mechanical. The electric current is required to produce the ozone, thc ozone acts chemically upon the water, and the water is mechanically raised to high towers and allowed to trickle down over the layer of pebbles, where it meets the ozone : furthermore, it may be necessary or advisable to subject it to a previous filtration. Dr. G. Erlwein having kindly supplied me with details of the Siemens- Halske process as it is carried out at Paderborn and Wiesbaden, I will describe the first of these installations, as it is typical of the plant which they are supplying, and has now been worked successfully for some years.The ozoniser employed is shown in Fig. I . It consists of concentric pipes A and E placed one within the other. The inner one is of aluminium, and is connected with the leads carrying a high tension84 THE INDUSTRIAL USES OF OZONE, PARTICULARLY current, niarked in the diagram as +, as this is the positive pole. As currents of the high voltage employed are very dangerous, the leading-in wires are very thoroughly insulated and are passed through the hollow hermetically sealed pillars and the frame of the ozoniser. The glass cylinder E is the other pole; it is surrounded with water which can be circulated for cooling purposes, and as this is “alive” it receives its charge from it. The water which surrounds the glass cylinder receives its electricity from the iron-containing box, which is earthed, and consequently forms the negative pole.The annular space between D and E is where the silent discharge takes place. The complete apparatus consists of a cast-iron box divided into three chambers, the lower chamber for receiving and conveying the air to the ozone tubes, an hermetically sealed middle com- partment into which the ozone tubes are inserted by means of a stuffing-box gland, and an upper compartment for collecting the ozonised air. Fig. 2 shows the apparatus as it appears closed up. FIG. 4. A plate-glass inspection window is fitted to each apparatus, so that it is easy to see whether it is functioning properly owing to the appearance of the blue discharge. The ozone-room in which the ozonisers are kept is usually dark to enable the attendant upon entering it to see at a glance whether they are working properly-ie., whether the apparatus has a uniform bluish glow.An ozoniser of this construction carries an alternating current having a potential of 8,000 volts ; I h.p. per hour is required to operate it, and from 13.5 to 27 grm. of ozone is generated in that time, depending upon the amount of air which passes through the ozoniser and upon the degree to which it has been previously dried. The water at Paderborn and Wies- baden requires an average coilsumption of 1.3 grm. of ozone per cubic metre (35.3 cubic ft.). Consequently, taking the daily consumption of water at IOO litres per head of population, each ozoniser is capable of sterilising water in twenty-four hours sufficient for a town of from 2,400 to 4,800 inhabitants. The figure IOO litres per head is probably rather low for this country,FOR THE PURIFICATION OF WATER.85 therefore it is perhaps better to put the capacity of the ozonisers as sufficient for from 2,000 to 4,000 inhabitants. In the Paderborn works the installation consists of a battery of nine ozonisers, with two sterilisation towers erected outside the ozone chamber. The battery is made up of three independent sets, each consisting of three ozonisers arranged as shown in Fig. 3, which represents schematically the Paderborn plant. One of the three sets is kept in reserve while the other two are used to supply the sterilisation towers. The towers are 4 metres (141.2 ft.) high ; they are constructed of concrete and contain pebbles about the size of pigeon’s eggs.Over these pebbles the water trickles and is therefore broken up into a number of small streams so that a very large surface is exposed to the action of the ozonised air, which is forced under a gentle pressure up the towers by means of blowers. Each complete tower, as shown in Fig. 4, is divided into three parts-(I) the reservoir H for containing the water to be treated, ( 2 ) the sterilising compartment containing the pebbles, (3) the receptacle for collecting the treated water. The interior of each tower is divided by means of two partitions into four independent towers, all of which obtain their water from a common supply pipe with a valve C. Every single is divided by a grating into an upper and lower part pebbles 2 metres in thickness, and a 1ower.reservoir for STERlLlZATlOH TOWER tower or shaft containing the FIG.5. collecting the sterilised water. The water to be treated flows through the four-way supply pipe into each single tower ; here it passes through a sieve which causes it to fall in a fine shower on to the layer of pebbles through which it percolates, becoming ozonised, and finally collects in the reservoir. Each of the single towers is one square metre in cross-section, and about 15-20 cubic metres (529-706 cubic feet) of air passes through it in the twenty-four hours, At the sides of the tower cascades are built over which the escaping water flows to the final storage reservoir. All traces of dissolved ozone are thus lost by the contact with the atmosphere.The scrubber system is found to give better results than can be obtained by forcing ozonised air up through a large bulk of water, because, the water being in very thin layers ;is it percolates through the pebbles, a much larger surface is exposed to the action of the ozonised air than can be the case when the air is forced up in individual bubbles. In case of interruption either to the electric supply or to the blowers arrangements have been made by means of which the water is automatically shut off from the sterilising towers, thus preventing the inflow of unsterilised water into the town mains. For instance, if the current in one set of ozonisers be interrupted, thus stopping the ozone formation, a lever in connection with the electromagnet which is held in place by the passage of86 THE INDUSTRlAL USES OF OZONE, PARTICULARLY the current drops and closes an independent circuit, which in turn by electromagnetic action causes a floating conical rubber valve to drop and shut off the water supply to the four towers.On the other hand, should the blower break down, an aluminium disk which is inserted into the main air- pipe and kept raised by the pressure of the current of air as it passes under normal conditions drops, and likewise by electromagnetic action shuts off the water supply to the towers. In either case the fall of an indicator attached to the switch-board tells which set of apparatus is not working, a i d an alarm signal rings until the trouble is rectified ; consequently it is not possible for the pure water to become contaminated with the unsterilised water.The method just described is employed in cases where it is not required first to filter the water. Where the water contains suspended matter it is necessary to have a filtering plant in connection with the installation. The plant at Wiesbaden is arranged upon practically the same plan as that at Paderborn, and is constructed to treat 250 cubic metres (882.5 cubic ft.) of water per hour, which is obtained from springs situated near Schierstein, along a former arm of the Rhine. The plant is in duplicate, each part being capable of dealing with 125 cubic metres (451-25 cubic ft.) per hour, but as a rule only half the plant is in operation at one time, thus giving a reserve of roo per cent.Messrs. Siemens & Halske, besides fitting up large ozone plant, also build smaller laboratory and experimental apparatus to deal with small quantities of water, which can either be rised for purifying water on the experimental scale or might be used for oxidation of chemical products, and they are also suitable for use in dwellings or restaurants, &c. They have also shown their versatility by inventing and fitting up transportable apparatus which could either be used in war-time or for dealing with contaminated water supplies; and one has only to remember the terrible mortality from enteric fever which ensued in the Transvaal War to realise the importance of such a means of purifying water in camp and upon the battle-field, where ordinary filtering appliances would be useless and it is not always feasible to boil large quantities of water.The apparatus consists of two small wagons, each of which is hauled by one horse, The small dynamo and all the pumping appliances are worked by means of a petrol motor. This apparatus was employed in the recent Russo-Japanese War and gave the utmost satisfaction. Other cases where a portable steriliser might be of great use would be in cases of an epidemic where the water supply of towns or villages has become Contaminated. It is not so very long ago that a terrible outbreak of typhoid took place in Maidstone, and it will be remembered how great was the mortality. The source of the typhoid was ultimately traced back to the contamination of the water supply, and it was some considerable time before this became sufficiently pure to be again employed.One might not like the idea of drinking water containing dead typhoid germs, but it is certainly better than drinking water containing live germs, and in the case of ozonisation pathogenic bacteria are very susceptible to the action of the ozone. The compended table shows how complete the sterilisation of water is after ozonisation, and it will be noticed that where germs remain in the water they are of a harmless nature and non-pathogenic. The tables given only include a few cases, but both in France and in Germany, where so much work has been done with ozonisation. Similar results have been obtained in iiumerous cases in this country and abroad. Fig. 5 illustrates the Paderborn water sterilisation plant.FOR T H E PURIFICATION OF 1VATER.Before Ozonisation. 87 After Treatment. Source of Water. BACTERI 0 LOG1 C.4L RESULTS. Ozone Exferimeiztal Works, Martinkenfelde. Number of Bacteria per Cubic Centimetre of Water. Species of Bacteria Number after I Ozonisation. Ordinary. Pathogenic. i Source. 0 I 0 2 Cholera. Typhus. River Spree 9 , 9 9 7 7 >7 Spree water infected with cholera. Boiled water infected with typhus. Number before Ozonisation. 8 9 0 0 The operating costs are by no means high : at Paderborn only two men are required to look after the whole installation, so that the cost of labour is a comparatively small item. It is stated that a plant capable of treating two thousand cubic metres (70,640 cubic ft.) of water per hour requires 275 h.p., while 45+ h.p.is necessary for a plant capable of treating 200 cubic metres (7,064 cubic ft.) per hour. This works out at about wid. for the larger plant and about ad. for the smaller plant. These numbers refer to steam plant; if producer gas is employed the cost is slightly less. Of course the purity of the water to be treated also has a considerabie bearing upon the cost. The purer it is in the initial stage the less ozone is required to purify it, whereas if the water were very impure necessarily require to yield a product richer in ozone. THE OTTO SYSTEM. Another process which has been found to work very large scale for the purification of potable water is the the ozoniser would successfully upon a Otto system. The FIG. 6. ozoniser itself consists of a series of transverse plates so arranged that a dielectric plate is placed between each electrode plate, the arrangement being electrode, dielectric electrode, and is shown diagrammatically in Fig.6. VOL. IV--T588 THE INDUSTRIAL USES OF OZONE, PARTICULARLY The air is drawn or blown between the plates, the silent discharge passing between the spaces of the plates and thus ozonising the air or oxygen. There are an odd number of electrodes similar in arrangement to an accumulator, the odd and even being connected to separate poles of the source of current, the whole system being held in a frame. I 1 FIG. 7. Fig. 7 gives an idea of the manner in which the air passes over the plates. The alternating current machine of particular design is employed and the best results are said to be obtained with a pressure of 6,500 volts, the current intensity being 0*00146 ampere.Under these conditions the apparatus can FIG. 8. be used for hours without any appreciable warming taking place. The more rapidly the air is passed through the ozoniser, the better the yield of the ozone.88 THE INDUSTRIAL USES OF OZONE, PARTICULARLY The air is drawn or blown between the plates, the silent discharge passing between the spaces of the plates and thus ozonising the air or oxygen. There are an odd number of electrodes similar in arrangement to an accumulator, the odd and even being connected to separate poles of the source of current, the whole system being held in a frame. I 1 FIG. 7. Fig. 7 gives an idea of the manner in which the air passes over the plates.The alternating current machine of particular design is employed and the best results are said to be obtained with a pressure of 6,500 volts, the current intensity being 0*00146 ampere. Under these conditions the apparatus can FIG. 8. be used for hours without any appreciable warming taking place. The more rapidly the air is passed through the ozoniser, the better the yield of the ozone.FOR THE PURIFICATION OF WATER. 89 Another form in which revolving electrodes are enclosed in a metal chamber which forms one pole, employs a current with a tension of about 25,000 volts, and is stated to be very efficient when large volumes of air have to be dealt with. The Lahmeyer Electrical Company, Ltd., who are the agents i n this country for the Otto processj have also a very useful little apparatus for the sterilisation of domestic water supplies.The ozoniser works directly on to the water supply, and is automatically set in action by turning on the tap. The apparatus is worked from an ordinary 16-cap. lighting socket, and is designed for use upon IOO to 250 volt mains. If the current is alternatiiig it is transformed up to 3,500-8,000 volts. If it is direct then a small motor converter is supplied with the apparatus. Fig. 8 illustrates the manner in which the apparatus is connected with the water tap, and explains itself without further description. Fig. 9 shows the whole apparatus fitted up ready for use. Recently a slight modification has been made in the apparatus by the fixing of a better “emulsifier” for mixing the ozone with the water, which is much more efficient than the one shown in the illustration.The whole apparatus, together with the transformer, does not occupy more than 1-25 square feet of wall space. Such an ozoniser is capable of sterilising 250 quarts of water per hour, which of course is much more than would be needed for ordinary domestic requirements. At the moment of being drawn off the water has a distinct smell of ozone, but if it be poured from a jug into a tumbler the smell will be noticed to have completely vanished and no taste of ozone can be noticed on drinking the water. At the same time, it is probably advisable to allow the water to stand ten minutes or so in order that there shall be no doubt about the complete absence of ozorie. The ozone having done its work-that is, having sterilised the water-one does not desire to drink a disinfectant.As a matter of fact if the water is allowed to stand for ten minutes or is poured from the jug to the glass and back again and then again into the glass, no ozone remains, but the water contains slightly more free oxygen than ordinary water, and this is an advantage rather than a dis- advantage. Over five hundred of these ozonisers have been installed by the French Government in Paris. The Otto process, like the Siemens-Halske process, is also employed upon a very large scale for the sterilisation of water for towns and cities. At Nice an installation for treating 5,000,000 gallons per day has been in opera- tion for about three years.The circuit from which the power is taken is three-phase, and has a pressure of 10,000 volts at 25 cycles. The potential is reduced by means of a transformer to 220-110 volts. The motor for driving the circulating pump and alternator runs at 220 volts. The alternator generating at 220 volts and 500 cycles is transformed up to 20,000 volts, this high pressure being employed to excite the ozonisers. The process is also in operation in Paris, Dinard, Chantenay, Saint Servain, and other towns in France. The great advantage in employing ozone for tlie sterilisation of water supplies which are to be employed for drinking purposes is that no noxious material remains behind in the water. The ozone acts as an oxidising agent, gives up one atom of oxygen in the process, and there remains behind in the water simply oxygen ; that is to say, the water is more thoroughly aerated after the process of ozonisation than before.I should not be inclined to entirely dispense with filtration, but as the process is so extremely cheap, is so efficient, and so absolutely harmless, it certainly seems that the time has come for sanitary authorities to seriously90 THE INDUSTRIAL USES OF OZONE, PARTICULARLY consider the employment of ozone for sterilisation purposes to guard against the outbreak of epidemics. OTHER USES OF OZONE. Ozone is employed for sterilising the air of rooms and buildings. There are various forms of ozonisers employed for this purpose. In one case an ozone tube somewhat similar to the old Siemens tube is fitted on to a fan and rotated with it.The rotation causes air to be drawn through the tube and out again into the air. There is also an apparatus of the Otto type where ozonised air is blown into the room by means of a small electro-motor, which, as it revolves, works a blower and at the same time excites the ozoniser.::: Ozone is also used for maturing wines and in particular spirits. Spirit which would requirc years for ageing is matured in the space of a few minutes by emulsifying it with ozonised air. It has also been used for sterilising beer-barrels, which have, owing to secondary fermentation, an unpleasant smell, and are known in the trade as “stinkers.” It is also largely employed for bleaching flour and wheat. In this case, however, the apparatus is on a different principle.Ordinary air is passed through the filter and then supplied by a blower to the ozoniser, and thus becomes ozonised. The air is then passed through a spark-box, where a very small proportion of oxides of nitrogen would appear to be produced by the sparks passing in between the sparks in the box. In bleaching the flour the normal ainount of air passed through the ozoniser is practically roo cubic feet per minute. The resulting gas, which is air and ozone mixed with oxides of nitrogen, contains in every 40,000 parts by volume three parts of ozone and one part of oxides of nitrogen. The current is o-og ampere and the voltage employed about IO,OOQ. The ozonised air passing at this rate will sterilise and bleach as much as three tons of flour in one hour, which is an extraordinary effect when one considers the small amount of the bleaching agents employed. As showing that sterilisation as well as bleaching takes place, unbleached rye-meal contains 2,400 micro-organisms, and after bleaching 1,600 per grm. Unbleached wheat flour contains 540 organisms and after bleaching 170. Vanillin is another product which is manufactured by means of the oxidising action of ozone. Eugenol is first converted into izo-eugenol by means of caustic alkali ; the alkaline solution of iso-eugenol is then sprayed into a chamber, where it meets a current of ozone, and it is by this means oxidised into vanillin. When crystallised it is ready for the market. NoTE.-There has lately been a considerable correspondence in the daily Press in reference to the domestic use of ozone, for sterilisation of water and purification of the air in rooms, &c., it having been maintained that its use in this way is dangerous. Personally, I am not inclined to agree with this dictum. Breathed in large quantities, ozone produces a feeling of nausea, but that quickly goes off, and personally, although I have worked for weeks at a time in a small room the atmosphere of which was saturated with the gas, I have experienced no ill effects. When employed for sterilising water the excess of ozone almost immediately goes off. The personal equation may, however, have something to do with the effect of the gas when breathed in large quantities. consisting of aluminium gauze separated by a mica dielectric. * The Ozonair Company, by means of a fan, draw air through an ozoniser