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November 29, 1917
ENGINEERING NEWS-RECORD
Vol. 79, No. 22
Page 1021
Ultra-Violet Rays Finish Treatment of Henderson Water-Supply
Sedimentation, Mechanical Filter and Ultra-Violet Purification Plant Has Been in Service Several Months – New Form of Sterilizer Used – Typical Bacterial Results
BY A.T. SMITH
R. U. V. Co., Inc., New York City
The large pressure-type ultra-violet-ray sterilizers now in operation at Henderson, Ky., are the first of this type in the world designed for use in connection with municipal water-works. The water delivered to the sterilizer is first passed through sedimentation and coagulating basins and mechanical filters, and after this treatment it is at all times virtually clear. The sterilizer units are automatic in operation.
The City of Henderson, Ky., located on the Ohio River, about twelve miles below Evansville, Ind., secures its water-supply from the Ohio River. It has a population of about 17,000. Up to 1916, untreated water was pumped to a 4,000,000-gal. reservoir. The storage was equivalent to less than two days’ supply, the average daily consumption being about 2,500,000 gallons.
The city, after considering various schemes, finally accepted the joint proposition of the R. U. V. Co., of New York City, and the Pittsburgh Filter Manufacturing Co., of Pittsburgh, for a complete sedimentation, filtration and sterilization plant at the pumping-station site, to have a nominal capacity of 3,000,000 gal. per day and designed to be increased to double that capacity without affecting the present structures.
The design was passed upon by J. W. Ellms, consulting engineer, Cincinnati, Ohio. There are two coagulating basins, each 95 ft. long, 30 ft. wide and 16 ft. in depth; and two baffled mixing chambers, 7½ ft. wide, 25 ft. long, and 17½ ft. in depth. The detention period in the coagulating basins is four hours on a capacity of 3,750,000 gal. per day, and the capacity of the two settling basins is 620,000 gal. Six reinforced-concrete filter units were installed, each 17 ft. long by 13 ft. 4 in. wide, with a normal capacity of 625,000 gal. each, totaling 3,750,000 gal. per day.
The filters are of reinforced-concrete throughout, with a brick building covering the filters and the head house. A clear-well covers the entire area below the filter units and pipe gallery. Adjacent to this, on the outside, is a low reinforced-concrete building, 17 ft. wide by 28 ft. long, in which is placed the ultra-violet-ray sterilization apparatus.
The ultra-violet-ray sterilizers consist of three legs, each comprising five units. The legs are connected in parallel, while the entire equipment is connected in series with the pipe line leading from the clear-water basin to the sump from which the pumps draw their supply. Valved increasers and reducers are provided to connect the sterilizer with the service pipe line, as the sterilizer units are made 30 in. in diameter to secure low velocity.
Each unit has a lamp box inserted in its side, equipped with a clear quartz closed-end tube, which projects into the body of the unit and around which the water is forced to flow in a thin film, by means of a baffle placed at 90° to the long axis of the sterilizer. The baffle has a slotted opening to receive the quartz tube and to provide for passage of the water.
Inside the quartz tube is placed a. 220-volt direct current mercury vapor arc lamp. It is properly held in place and automatically tilted by a special support which is located in the lamp box.
An iron baffle plate with four large holes is inserted in each unit to insure bringing each particle of water into the field of the ultra-violet rays during its passage through the apparatus.
Each lamp is provided with a small individual switch cabinet to provide proper electrical starting characteristics. A main switchboard is also provided and placed adjacent to the filter-operating room. This board has mounted on it a tell-tale incandescent lamp for each ultra-violet lamp in the sterilizer, main-line switches and indicating instruments. There is also a warning bell which rings when a tell-tale lamp is lighted.
If any ultra-violet lamp fails or diminishes in power from any cause, the bell rings and the tell-tale lamp on the main switchboard shows which lamp or lamps in the sterilizer are in trouble.
A motor generator set is provided to transform the available alternating current into 220-volt direct-current.
The accompanying tabulated results have been taken from daily tests run continuously for over two months and are offered to indicate the effectiveness of the sterilizer.
The bacteriological work was done in accordance with standard methods of the Laboratory Section of the American Public Health Association, and the average results were closely checked by the maximum and minimum obtained, which vary little from average results.
The plant was put in operation toward the end of 1916 and has since run under a varying capacity from 2,200,000 to about 3,500,000 gal. per day. The current consumption guarantee of 0.77 per lamp was met in operation. The cost of final sterilization by this method can be estimated from the current consumption, which is 92.5 kw.-hr. per 1,000,000 gallons.
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