water Sterilizing Plant at St. Petersburg
The city of St. Petersburg. Russia, has recently installed a large ozone water-sterilizing plant, with a view to stopping typhus, which is always endemic and to suppressing the cholera endemics, which have recurred annually for some years. The new ozone-sterilizing plant has been added to one of the municipality waterworks, which pumps the ordinary Neva river water direct into the municipal mains. The daily capacity of this waterworks is about 11,000.000 gallons. Before the ozoning process, the water is subjected to clarification and rapid filtration in order to remove the impurities in suspension resulting from the excessive pollution which it undergoes during the period when the ice breaks up. The water-sterilizing plant consists essentially of two main parts, the filtration plant and the ozonesterilizing plant. The water is pumped direct from the Neva river into the clarifying reservoirs, a solution of alum of suitable concentration being added in accordance with the well-known American system. The clarifying reservoirs are eight in number; they are connected by means of pipes to the rapid filters, thirty-eight in number. These filters are of the Howatson type, somewhat similar to the American Jewell filters, but in place of fine filter sand, specially prepared flint is employed. The rate of filtration is about 92 gallons per square foot per hour. The filters are cleaned in the usual manner, by back-rinsing with filtered water, the flint being stirred by suitable gear. The filtered water is taken direct to the sterilizing towers through a ring-main, a small part being diverted into a reservoir, where it is collected for rinsing the filters. In contradistinction to slowly percolating sand filters, the duty of the rapid filters is not to stop bacteria, but merely to retain the impurities and coloring matter in suspensionin the impure water. The actual ozone plant is connected to the filtration plant and also consists of two parts, viz., the ozone battery and the sterilizing tow ers. The former consists of 128 elements, while the latter comprise five towers, of which one is a spare. The ozone battery is built up of S iernens & Halske ozone tube dements, in which the oxygen in the air is converted into ozone by high-tension silent discharges. The brush discharges take place between cylindrical poles of aluminum and glass. The concentration of ozone isdetermiined to suit the method of working of the towers, at the comparatively high value of 0.07. Before entering the ozone battery, the air passes through a cooling apparatus in which it is brought to the degree of dryness necessary for the production of ozone. The movement of air through the ozone battery and the pipes connecting it with the towers is effected by the so-called emulsifiers which are fitted in the towers. These Otto system emulsifiers, or water-jet air pumps, suck the ozonized air out of the ozone battery, and eject it, mixed with the water, into the sterilizing towers. The absorption of ozone and simultaneous sterilizing of the water is effected partly in the emulsifiers and partly in the towers, from the bottom of which the gas rises in a very finely divided state, and hence in very intimate contact with the water.’ The latter is discharged from the towers over de-aerating cascades into a discharge pipe, which conveys it to the pure water reservoirs, whence it reaches the high-pressure pumps, which force it into the municipal mains In the power house two 150-horsepowcr steam engines direct connected to three-phase generators have been provided for running the plant. Three high-frequency rotary transformers raise the periodicity at which the current is generated to 500 cycles per second, after which the current is stepped up, by static transformers, to a pressure of about 7,000 volts for the ozone battery. The dirty water of the Neva river is converted into clear, pure and healthy drinking water, the bacteriological index of which is very low, and the pathogenic germs of cholera, typhus, etc., are entire y absent. The running costs amount to about 1 cent per 1,000 gallons, of which less than half is for the ozonizing process.—Scientific American.