Sterilization of Water by Ultra-Violet Light as Emitted by the Carbon Arc

Abstract

In two previous papers (1) the authors demonstrated the rapid bactericidal action of ultra-violet light under definite experimental conditions. The absence of the so-called lag period was shown as well as the small amount of interference necessary to prevent this rapid action. The effect of a concentration of organisms below the line of visibility as well as the presence of a group was further demonstrated. All the experiments were done on a pure science basis with no thought of practical applications. The present paper attempts to apply the results of former investigations. In the earlier papers it was recorded that results of exposure 20 inches from the light for short periods were as satisfactory as much shorter distances, indicating that the increase in distance was still within the limits of the efficiency of the iamp used. Further, it was found that the result was practically the same whether there was air or clear still water between the quartz tubes and the light source. In our conclusions we stated our belief that the action of the light, when the suspended matter was small in amount, was instantaneous and also that even with short exposures, all save the small resistant group would disappear. This group always persisted for a long time, far beyond the ordinary period used in sterilization. If these ideas were correct, and the apparatus was so arranged that there would be an adequate exposure of a moving body of water a full 12 inches in maximum radial distance from the arc, it followed logically that a very brief exposure would be sufficient to kill all save the resistant group. Inasmuch as the usual allowed distance is far shorter than this, the possibility of sterilizing with one lamp more than the amount usually treated with a series became evident. Parkinson (2), who is experienced in the field of water sterilization,