CHAPTER XI

ULTRA-VIOLET RAY TREATMENT

The ultra-violet ray process of water disinfection has found favor where the volume of water to be treated is relatively small or where automatic sterilization is of prime importance. Of several hundred ultra-violet installations in this country the majority are used for treatment of swimming pools. Other uses are in connection with bottled water and soft drink establishments, drinking water supplies for hotels and industrial plants. There are about 60 installations on steamers plying the Great Lakes. Of installations treating municipal water supply that of Henderson, Ky., made in 1916-17, is the largest. Advices from Henderson (January 19, 1925) indicate that from 2.5 to 3 million gallons of water were treated per day at a monthly cost of about $125 for electric current and $60 for lamp repairs and renewals. The process has not been in use for over a year and no plans have been made for its future employment, liquid chlorine having been substituted because of the difficulty experienced in keeping the lamps in working order. Other municipal water supply installations are those at Berea, Ohio, 1923, and Horton, Kans., 1924, both treating filtered water at a rate of 0.5 m.g.d.

The process consists in the direct application of ultra-violet rays. to water as it flows through a channel or pipe containing a succession of restricted orifices wherein the depth of penetration of the rays can be governed. In each of these orifices or ports, quartz lamps containing mercury are set from which the rays issue and penetrate the water flowing by them. The lamps are arranged in tandem. on the principle that, if the desired result is not obtained from the first lamp, it will be by the succeeding lamps.

In ordinary practice the lamps use a direct current of 220 volts and 3.5 amperes. It usually requires about ten minutes to develop the full voltage across the lamp. The intensity of illumination is a factor dependent upon the power and number of the lamps, their spacing, and the general design of the sterilizing chamber. The effective penetration of the rays in a clear and relatively colorless

water is about 5 inches, the passages in which the lamps are set usually being about 80 square inches in area.

The velocity of flow of water past the lamps (period of contact with the rays) is a function of the head lost by forcing the water through the restricted orifices. The period of contact is of less importance than the distance factor (ray penetration) so far as the sterilizing effect is concerned. The number of contacts required (number of lamps in series) depends upon the degree of sterilization desired. In addition to their normal deterioration, the life of the lamps depends somewhat upon the character of the water.

The efficiency of the ultra-violet ray process is restricted to disinfection. Bacterial reduction is affected by the degree of clearness and color of the water. If the unsterilized water contains over 15 parts per million of turbidity or color the process is relatively ineffective. Where such turbidity is caused by finely divided or clumped suspended matter the direct action of the rays upon bacteria or other microscopic life is measurably diminished, and bacteria embedded within particles of suspended matter pass by the lamps unharmed. Air bubbles in the flowing water do not affect the disinfecting action. Reflected rays have little, if any, disinfecting action.

If the unsterilized water is not highly polluted, is clear and practically colorless, and if, say, 6 lamps are used to treat 250,000 to 500,000 gallons of water daily, the removal of bacteria, subject to the usual variations, may roughly be assumed at 30, 45, 60, 70, 90, and 99+ per cent after passing each lamp in series.

The process is attractive because nothing is added to the water which may impart offensive tastes and odors. The system requires constant watching, for, if the lamps are not working properly, they will go out automatically. It is more expensive than other forms. of water disinfection now in use. The electric current supply must, of course, be uninterrupted, and, as stated before, it is futile to attempt efficient disinfection with the ultra-violet ray process, if the turbidity and color of the untreated water exceed 15 parts per million.

OZONIZATION

Ozone is an active form of oxygen and may be produced by passing a current of air over a brush discharge that takes place between

the electrodes connected to a high voltage alternating current circuit. Ozone generators are designed generally with a solid dielectric interposed between the electrodes. All ozonization plants for the purification of water consist of two parts, the generators where the oxygen in the air is converted into ozone, and the scrubbers employed to bring the gas into intimate contact with the water. Nearly all of the many generators for the production of ozone have followed practically the same general design and operate in a similar way. They consist of an inside and outside electrode with a dielectric interposed between them. The elements are so placed as to permit air to be drawn or forced through the space between the electrodes. Usually the generators are cooled, and the air passing to the apparatus is dehydrated either chemically or by refrigeration. The amount of oxygen converted into ozone per unit of electrical energy expended varies with different machines.

The method employed to bring ozonized air into contact with the water is much the same in all systems. The ozone mixed with air is discharged into a scrubber chamber and thoroughly mixed with the water by passing through a bed of gravel, or by means of baffle plates. In the plant at Petrograd, Russia, gas scrubbing is used.

In 1919 there were between 60 and 70 municipalities in Europe employing ozone for the sterilization of public water supplies. The majority of these plants now in use are comparatively small, although some large units have been constructed and operated. The St. Maur system at Paris, with a daily capacity of 24,000,000 gallons, and the Petrograd plant in Russia, treating about 13,000,000 gallons of water daily, are notable installations.

Ozonization systems for the treatment of public water supplies in America have not proven successful, although many attempts have been made to use them. The efficiency of ozonization depends largely upon a thorough mixing of gas and water and an adequate contact period. The failure of many plants to function satisfactorily has been due to inefficient mixing. Water that contains suspended solids or is highly colored should receive preliminary treatment to remove these constitutents. Since ozone is an active ozidizing agent it may reduce the color in water, if it is of an organic nature. It is much cheaper, however, to remove such substances by filtration or treatment with chemicals, than by ozonization.

Ozone is a fairly efficient bactericide, but, for continuous effective

ness, the gas must come into direct contact with the organisms and must be in sufficient concentration. When these conditions are fulfilled complete sterilization is possible. Concentrations as low as one gram of ozone per cubic meter of air will sterilize some waters. The cost of ozone treatment is greatly in excess of chlorination.

CHAPTER XII

TREATMENT OF WATER WITH IODIDE FOR THE PREVENTION OF SIMPLE

GOITER

Introductory

A public health measure of absorbing interest and outstanding importance has gradually been introduced in this country during the last ten years. In the prevention of simple goiter by the administration of minute quantities of any form of iodin we possess an effective prophylactic against thyroid enlargement, especially during those periods of life when it is most prone to occur.

Simple goiter may be described briefly as an enlargement or swelling of the thyroid gland-a gland of internal secretion-which lies in the front part and somewhat to the sides of the neck. It may involve either one or both lobes of the gland and vary in size from the normal, which can scarcely be noticed, to the pendulous forms.

Two other types of goiter usually more serious in nature should be mentioned; one a definite nodular tumor which may undergo malignant changes and the so-called exophthalmic or toxic goiter associated with profound nervous symptoms and disturbed metabolism. With these forms iodin prophylaxis is not concerned. The treatment and cure of different kinds of goiter is strictly a medical and surgical matter. Many forms of treatment and prevention have been tried all the way from incantations and amulets to radical surgical operation. No form of prevention, however, has given so much promise and proved so uniformly successful as the early administration of small quantities of some form of iodin. The prevention of simple or endemic goiter, therefore, may be considered a public health problem of prime importance.

Historical

The enlargement of the thyroid, now generally known as goiter, has been recognized as an abnormal condition for many centuries. There is some evidence that as far back as 2000 B.C. the Chinese were familiar with it and discovered that the eating of sea-weed and