FILTRATION AT ALEXANDRIA.
Sketch of the Alexandria Water Company and the Jewell Filter Plant.
The present Alexandria waterworks were constructed about the year 1860, by the Egyptian government, in the reign of Ismail, under the direction of M. Cordier, a French engineer, who built the original works. The waterworks were purchased by an English company, which is the present Alexandria Water Company, Limited, about twenty-five years ago, but today a comparatively small proportion of the shares are held in England, and the whole of the board of directors now consists of residents of Alexandria. The progress of the company has been extremely steady and most interesting, as well as full of adventurous incidents. During the bombardment of Alexandria by the British ships at the time of Arabi Pasha’s rebellion in 1882, the waterworks were in imminent danger of being destroyed; and undoubtedly would have been, had it not been for the remarkable and distinguished bravery of J. E. Cornish, the present managing director of the company. who, with a few native stokers (the Europeans having deserted him), not only remained at his post and kept the engine running himself, but also placed _____e premises in a complete state of defence, and so preserved them. The value of the water installation and the capital is now $2,500,000, and the company is in a prosperous condition. The total number of customers is over 12,000 in Alexandria, and over 700 in the outlying suburb of Ramleh, the total population of the two places being nearly 400.000. I here are at present three slow sand filter beds at Alexandria, having a total area of filtering surface of about 1.4 acres. The water company possesses three district pumping stations: 1.—The main pumping station for Alexandria, situated a short distance to the east of the city, near Rosetta gate. 2.—The small pumping station situated on the Mahmoudieh canal, about ,_____,000 feet from the main pumping station. 4.—The pumping station for Ramleh, situated at the village of Hagar-el-Nawatia. about four miles farther tin the Mahmoudieh canal than station No. 2. In the main city pumping station the old engines are arranged to drive a low-service and a high-service pump—one on each side of the beam. The lowservice pumps take their water from an underground culvert, which is connected with the Mahmoudieh canal, and deliver it into the existing filter beds at a total height of thirty-three feet. The high-service pumps take their water after it has passed through the filters, and deliver it through a twenty-four-inch and twenty-inch-pipe into the main reservoir at Kom el Dick, against a head of about ninety feet, from whence it is distributed into the city. The reservoir is of wrought iron, 150 feet in diameter by fifteen feet eight inches deep, and, when full, contains about onequarter of a day’s supply The water cornpany, in order to fulfill its obligations laid down in the convention with the Egyptian government at the time of purchase, was not obliged, beyond supplying filteredwater to the city, to guarantee any particular degree of purity or bacteriological removal, and it is in order to obtain a really efficient and reliable filter installation that the municipality combined with the water company to share the heavy expense which will be incurred by such an installation. Plans and estimates were prepared of a slow sand filter plant, and the scheme was very nearly actually commenced, when the Jewell Export Filter company, approaching the water company and the municipality, with a view to inducing them to adopt the Jewell system of filtration, offered to install at Alexandria, free of all cost, a complete Jewell gravity experimental filter plant, with all accessories,including engine, pumps, settling basins and filter, capable of dealing with a minimum of 22,000 imperial gallons per day. This plant, illustrated herewith, was installed in October, 1902. and was kept at work night and day incessantly for about eight weeks, the experiments being conducted by E. A. Gieseler, representing the Jewell Expert Filter company; by Dr. Bitter, representing the Egyptian government; by Dr. E. Gotschlich, sanitary inspector of Alexandria; and by H. R. C. Blagden, chief engineer of the water company. The result was the decision to adopt the Jewell gravity system. The filter plant will consist of three masonry settling basins, each having 88,000 Imperial gallons. These will be circular, constructed of steel, and seventeen feet inside diameter. They will be eighteen in number and will have a total filtering capacity of 8,000,000 Imperial gallons per day. They will be mounted on circular masonry foundations, in a large filter house measuring about 138 feet long by 103 feet wide by twenty-two feet high, and will have all necessary shafting, etc., for working the stirring apparatus required for the cleaning process of the filters. Close to the filter house will be a small auxiliary house, containing on the ground floor vertical high-speed engines in duplicate for driving the shafting in the filter house, also centrifugal pumps for supplying the water for washing the filters, and a dynamo for furnishing the electric light for the whole premises. On an upper floor of the auxiliary house a complete apparatus will he installed for mixing, dissolving, and supplying the sulphate of alumina solution. Thence the solution will flow by gravity through a lead pipe into the thirty-inch low-service delivery pipe to the settling and coagulating basins. The three existing sand filter beds will be converted into clear water basins, and will contain about 1,320,500 Imperial gallons. All the existing low-service pumps will have to he modified to deal with the increased head of water required by the new Jewell filter plant, and two additional low-service engines and pumps will be added. The total cost of the new filter plant and necessary modifications to the present machinery and buildings which will he required is estimated at about $390,000. The whole of the work will be carried out in accordance with the designs, and under the supervision of H. R. C. Blaeden, chief engineer of the water company, who anticipates getting the whole plant to work within a period of two years. The second pumping station is situated on the Mahmoudieh canal at the intake from the canal, whose level is kent practically constant, being supplied direct from the Nile at Atfch, about forty miles away, and at low Nile, by large centrifugal oumps belonging to the Egyptian government, which undertakes to maintain the level of the canal. The water is pumped from this canal into the Farkha canal, to a height of two to three metres above the Mahmoudieh canal. The Farkha canal, which contains about thirty hours’ supply of treated water, acts as a settling basin for the water on its way to the pumping station. The Ramleh pumping station has its water supplied by numping direct from the Mahmoudieh canal into the mains, without any filtration whatever. The experimental filter plant was installed by the Jewell Export Filter company, of New York, and was especially designed and arranged under the direction of Edmund B. Weston, M. Am. Soc. C. E., M. Inst. C. E.. consulting engineer. Providence, R. I., U. S. A., who is also preparing the plans for the plant of the new Amsterdam System of filtration, to be installed by the Jewell Export Filter company of Alexandria. The Nile water, especially in the condition in which it comes to Alexandria, offers particular difficulties to filtration on account of the very fine particles of clay, which it holds in suspension. The previous English system of filtration having proved unsatisfactory, Dr. Bitter, director of the Egyptian State Institute of Hygiene, Cairo, advised the acceptance of the Jewell Export company’s offer above referred to. all the more that, by adopting that system, the municipality of Alexandria would save about $100.000. The experimental plant was, therefore, put up by E. A. Gieseler, engineer of the Jewell company, and he also supervised personally the technical operation of the filter during the whole time. It was erected on the bank of the Mahmoudieh canal, in close vicinity to the pumping station of the Alexandria water company. The raw water was taken from the canal, by means of a small steam pump, which was kept working by the water company day and night. The raw water was elevated into the first settling tank, where, on its entrance, it was mixed with the necessary amount of coagulant solution, by means of an automatically working apparatus. There were three subsidence basins, each of which contained about fifteen cubic metres (3,300 Imperial gallons) of water. The water circulated through the settling tanks in a continuous current, the speed of the pump having been regulated to the rate of filtration. The passage of the water from the entrance into the first tank to the outlet of the last tank took nine hours, so that the water remained in each basin for three hours. In the settling tanks the greater part of the finely suspended clay contained in the water, was deposited gradually by the action of the sulphate of aluminaIn each following basin the water left clearer than at its entrance, and at the last tank was only slightly turbid From that tank it en’ered by gravity through the pipe A into the filter, which is of the accustomed type, with the usual layers of fine and coarse sand and gravel (as shown in the accompanying diagram). The gravel is supported on screens screwed into a plate(c) of perforated iron. B is the annular space between the outer and over-topping steel cylinder and the inner one. The filtering surface is marked by a. C is the outflow pipe for the water that is filtered; E, the pipe through which the water above the filtering surface sinks to the level N, corresponding to the rim of the inner cylinder, completely emptying the annular space B. D is the pipe carrying filtered water all over the bottom of the filter bed. the water rising into the sand in the direction of the arrows shown in broken lines. In the beginning of the experiment thirtyfour grammes of sulphate of alumina were added to each cubic metre of raw water, and the time of subsidence was nine hours The results were excellent. But it was soon recognised that six hours’ subsidence was sufficient, and that even then the quantity of sulphate of alumina could he considerably reduced. Gradual reduction showed that twenty-two grammes of sulphate of alumina and a subsidence of six hours still gave quite satisfactory results, but that twenty grammes per cubic metre were not quite sufficient for obtaining an absolutely perfect result .of filtration. From the beginning of the experiments till the 26th of November the rate of filtration was regulated at ninety-six metres in twenty-four hours. From the 26th of November this rate was increased to 120 metres in twenty-four hours. The rapidity of filtration was, therefore, from 4,000 to 5,000 millimetres in an hour, or forty to fifty times more than admitted for the old sand filter beds. As regards clarification of the water : There were obtained most excellent results throughout the entire time the experiments were carried on, which results not only equaled those obtained by the best English filter beds, but were even superior to them in the absolute constancy and regularity with which they were obtained. As regards the bacteriological examination of the drinking water. Dr. Bitter thus states his opinion: “The Jewell filter is not only equal to the old English sand filter beds, hut I venture to say that it is distinctly superior to them. Another great advantage of the American filter is, that it possesses an almost ideal regulator of rapidity of filtration and of pressure. The quality of filtered water is absolutely constant during the entire duration of a run, and the diagram of pressure is perfectly regular During the whole time the experiments were carried on. a diagram of pressure was plotted for each run of the filter. They all showed the same regularity. This is a most important fact, as the perfect working of a sand filter in the first place depends on absolute constancy of the rate of filtration and absolute regularity of increase of pressure. The Weston regulator has this further advantage—that the filtering rate, in case of necessity, can be changed in a few minutes. This is of great importance in case there is, for any reason (for instance, fire), a sudden increase of consumption of filtered water. The greatest advantage of the Jewell filter from a technical point of view is the mechanical cleaning, which is executed with great facility and rapidity, and, at the same time, with a very high degree of efficiency.” Dr. Bitter had several samples of the filter bed sand taken both before and after cleaning taken from the surface down to a depth of twenty-five centimetres, the amount of impurities attached to the sand being determined bv weight. The results showed that practically. the impurities had not penetrated deeper into the filter bed than three or four centimetres, by far the greatest part having been retained at the surface and down to a depth of one centimetre. At a depth of five centimetres the sand (originally white) was but slightly yellowish; at ten centimetres it was nearly white; and in the deeper layers it was perfectly white. The samples of sand taken after cleaning. showed a considerable reduction of the amount of impurities in the upper ayers of the filter bed In the lower layers, that is from about ten centimetres below the surface downwards,the amount of impurities attached to the sand is nearly equal in both cases, that is to say, practically nil. It was thus seen that the impurities do not penetrate ch eper into the filter bed than they do in any good English sand filter. The operation of washing, as performed in the American Jewell filter, Dr. Bitter considers to be “ very thorough ” It “guarantees a nearly perpetual state of efficiency of the filter bed A complete renewal of the sand would hardly, if ever appear to he necessary. Only the small, unavoidable losses of sand which take place during washing have from time to time to be reolaoed. It may he mentioned here (Dr. Bitter adds) that installations are now made in which the entire working, the washing, the reopening of the filters, etc., is done by means of hydraulic apparatus operated automatically by a single person in a room above the filters. In this way the access of workmen to the filter itself is unnecessary, which, of course, is a great advantage” In summing up, his verdict is that all the results obtained during the experiments lead him to the conclusion “that the American system of filtration, as represented by the Jewell filter, has so many technical and hygienic advantages, that it should under all circumstances be preferred to the old project elaborated for the city of Alexandria.” The experimental filter plant was installed, at the request of the Alexandria authorities, by the Jewell Export Filter company, of New York, and was especially designed and arranged under the direction of Edmund B. Weston, M. Am Soc. C. E„ M. Inst. C. E., consulting engineer. Providence, R. I., U. S. A. .
Illustrations of the experimental filter in posit on have already appeared in this journal. In this impression are shown the section of the filter itself and the following illustrations: Main pumping station of the Alexandria Water company; residence of H. R. C. Blagdcn. chief engineer of the company, showing, also, the existing slow sand filters; boiler house, machine shop, and pumping stations of the company, and the existing slow sand filters; sand excavation made for the new sedimentation and coagulating basins of the company. The average depth of this excavation is thirty feet, and in making it an ancient Egyptian temple was discovered. The passage leading to the tombs can be seen in the illustration.
Concluded on page 243.