GB356783A - Improvements in or relating to the purification of liquids - Google Patents

Abstract

<PICT:0356783/III/1> <PICT:0356783/III/2> Liquid or solid perishable organic materials are treated with intense sound waves, including those of infra and supersonic frequencies, for the purpose of preservation or sterilization, the bacteria present being rendered permanently or temporarily innocuous, or destroyed. Solid materials or materials enclosed in tins &c. are preferably treated while immersed in a liquid or a substance liquid at the temperature used, or the liquid may be present naturally or otherwise, in the interstices of the solid materials. The sound waves are preferably applied intermittently. The higher frequencies are generally preferable, and the waves may be of a single frequency or of complex wave form. Some bacteria are affected by sound waves of different intensity to those required for others, and the intensity used can be adjusted for the particular case. The substance may be stirred or otherwise agitated during the treatment. The temperature used is below that of pasteurization and is above or below that favourable to propagation of the bacteria, e.g. milk may be treated at 115-140 DEG F., preferably at 120-135 DEG F. Low temperatures, e.g. about 32 DEG F., may also be employed, especially in the case of substances affected by the higher temperatures, and as low as 14 DEG F. can be used, e.g. in treating liquid eggs, freezing being avoided by vigorous stirring or circulation. The treatment chamber may be so constructed that, with its contents, it is substantially in resonance with the sound waves or a predominant frequency thereof, or tubes, rods, wires, or like devices suitably tuned to resonance may be provided in the chamber, to cause intense sound waves to pass through the substance in different directions. In an example, a liquid is treated in a chamber A having a cover B with a tube C the lower end of which dips in the liquid and is preferably open. A loud-speaker D, preferably of the moving coil type, is mounted within the tube C and is energized through a circuit E from a thermionic valve oscillator F and an amplifier G. A sound insulating hood P is fitted over the loud-speaker D and cover B. An interrupter is provided, consisting of a rotating insulating disc H having contacts H<1>, H<2>, H<3> thereon with which fixed brushes K, K<1>, K<2>, K<3> engage. The brushes K<1>, K<2>, K<3> can be connected one at a time by a switch L, which may be operated by hand or automatically, to one terminal of the loud-speaker D to complete the circuit. The interrupter allows the sound waves to be produced continuously or intermittently. The interruption period depends on the size of contacts H<2>, H<3> and can be varied by altering the speed of rotation of the disc H. An irregular sequence of interruptions can be produced by operating the switch L by hand or automatically at suitable intervals. The number and spacing of the contact rings on disc H may be varied, and other forms of interrupter may be used. The oscillator F has control devices of usual type to enable the frequency of the oscillations generated to be varied. The liquid in chamber A is kept in movement by a rotary stirrer M. The chamber A is surrounded by a jacket R containing water or other liquid heated by a steam coil S. In modified forms, the stirrer is omitted and the loud-speaker disposed centrally in the chamber, or the liquid kept stationary, and the loud-speaker moved past it. Other sound-emitting means, e.g. a whistle or reed, may replace the loud-speaker and the sound emitter may be partly or wholly immersed in the substance treated. Reference is made to the treatment of meat and fruit, canned or not, liquid eggs and milk.