Mr. Frank. As Prof. Phelps has told you, the Public Health Service, realizing the probable future necessity of treating the sewage from vessels in some way or another, has endeavored to find a practicable solution. So that for the past two years we have been studying various methods, and we have been experimenting with what seemed to be the best method.
The method of traffic-sewage control is to provide storage tanks for the sewage so equipped that the sewage is both automatically disinfected and automatically discharged by means of steam or other heating element when it has reached a certain predetermined level in the tank. This method has been described in Reprint No. 247 of the Public Health Service reports. Briefly, the device consists of a tank, as shown in the illustration, with a sewage influent pipe penetrating nearly to the bottom; a discharge pipe having its influent end near the bottom of the tank, and rising up through the tank to a point above it; a float and valve with a lost-motion connection; and a steam influent pipe. The operation of the tank is simple. When the sewage has reached a certain predetermined level the float automatically turns on the steam, which escapes into the sewage through a number of small holes. All of the heat of the steam, of course, is given up to the sewage, which rapidly approaches the boiling point. As soon as the boiling point is reached, but not before, pressure is developed in the tank and the sewage is forced up and out through the discharge pipe. When, owing to this discharge, the sewage level in the tank has dropped to a predetermined minimum the float, through its lost-motion connection, turns off the steam and the tank is ready for the next cycle of operation.
There are a number of distinct advantages of this method:
(a) It depends upon heat for its disinfection efficiency, and heat is generally acknowledged, as above noted, to be very thorough in its action.
(b) Its action is entirely automatic. This eliminates the uncertainties of manual operation by a large number of employees.
(c) If fresh sewage enters the device while it is being discharged, the discharge immediately ceases.
There is no danger, therefore, of fresh sewage being carried out untreated. This advantageous feature is due to the fact that as soon as any fresh sewage enters the device its contents are chilled to a temperature at which pressure is impossible. The new mixture must again be brought to the boiling point before further discharge will take place.
(d) It permits toilet doors to remain unlocked over drinking-water areas.
(e) It permits toilet doors to remain unlocked while waiting in stations. This latter has, of course, no public-health significance, but it does concern very nearly the comfort of the passengers. In lieu of locking the toilet doors while standing in stations, the porter has merely to turn off a steam valve penetrating the car floor external to the toilet. The tank can be designed with a sufficient reserve capacity to care for any reasonable period of waiting. The objection will be raised immediately, of course, that the porter may forget to turn on the valve when the train leaves the station. This is true, but forgetfulness of this sort will rapidly create its own remedy. For, at the station stop immediately subsequent to the complete filling of the tank and its consequent dribbling, the fact of the porter’s forgetfulness would be made painfully evident by toilet discharges upon the station platform. It should be remembered in this connection that the porter can not help himself in such an emergency by locking the toilet doors.
The above device is now being experimented with upon a stationary basis in order to secure the maximum simplification of details and to secure data upon steam consumption, and bacterial efficiency. As soon as these studies are completed experimental devices will be placed upon vessels and railway coaches and tested in actual service. It is believed that the cost of operation will be extremely low. Rough preliminary office estimates indicate that the cost of disinfection with the above device should not be over two-tenths of a cent per cubic foot of sewage disinfected. This preliminary estimate is based upon the assumption that 1 pound of coal in the average modern locomotive will evaporate 6 pounds of water, and that locomotive coal costs $1.50 per ton delivered into the locomotive. This certainly should be more than sufficient allowance for radiation.