The largest slow sand filtration plant in the United States treats a part of the water supply of Albany, N. Y. It was designed primarily to remove bacteria from the badly polluted water of the Hudson river, and secondarily to remove turbidity and effect such a reduction of color as might be feasible. The plant was completed in 1899 with Allen 'Hazen. of New York, as engineer. Centrifugal pumps lift the water 24 feet or less, according to the river level, lifter which it passes through a. 36-inch Venturi meter to and through 11 vertical perforated pipes, which afford some aeration as they discharge the water into a set tling reservoir. The reservoir is 333 X 600 feet in plan, has a water depth of nine feet, and a capacity of 14.600,000 gallons. Eleven outlets discharge the water through proper pipes upon eight filter beds having a combined area of 5.6 acres, which, at a nominal rate of 3,000.000 gal lons an acre, have a total daily capacity of 14, 700A00 gallons. From the filters the water passes to a small, equalizing clear-water reser voir, having a capacity of 600,000 gallons. From this reservoir it flows through a steel conduit to a second pumping station, for delivery to the reservoirs and consumers. The filter beds and clear-water reservoirs are covered. The cost of this whole plant was: $86.638 for the steel conduit to connect with the old pumping sta tion; settling reeervoir, about $60,000: clear water reservoir, $9.000; filter boils. $2.15,000. Thus the filters alone cost about $17,000 per 1,000,000 gallons of rated capacity.
From July 26, Nun, when the Albany purifica tion works were put in use, to December 29, 1901, an average of 6,463,000 gallons of water per day was treated, at a cost of $1.66 per 1,000,000 gal lons for filtration alone, and $4.52 for pumping to the settling basins, cleaning the latter, filtra tion and laboratory expenses. The $1.60 of ex pense for filtration alone was divided as follows: Scraping sand from beds, 24 cents: wheeling out sand, 42 cents; replacing sand, 32 cents: inci dentals. 13 cents; lost time, 10 cents. The bac terial reduction was about 09 per cent. Prac tically all of the turbidity was removed and the color was reduced by 24 per cent.
The first mechanical filter connected with a municipal water supply was put in operation at Raritan, N..1.. in 1884 by the Somerville Water Company. which supplies Raritan and Somer ville. No coagulant was used. In 1883, John W. Ilyatt patented a filter of the same general type as the one erected at Raritan. In February. 1884, Isaiah S. Hyatt. a brother of John. patented a system of coagulation and filtra tion combined. These and other patents granted to the Hyatt brothers formed the basis of the Hyatt and later on the New York mechanical filters. Rivals appeared in the market from time
to time and much litigation ensued. The latter was confined chiefly to the use of a coagulant. In 1897 the United States Cirenit Court of Ap peals, notwithstanding much expert and other testimony designed to show the prior use of coagulating materials coincident with filtration, declared the Hyatt patent valid. The patent ex pired early in 1901.
For a number of years the use of mechanical filters was confined almost wholly to the produc tion of a bright, clear water. Very little dis interested evidence was available to show their efficiency in this respect and practically none bearing on their bacterial efficiency. In 1893-94 experiments on a small scale were made under the direction of Edmund B. Weston, at Provi dence, R. I., which indicated that mechanical filters would remove a high percentage of bac teria. In 1505.07 more extensive investigations, on a large scale, were made at Louisville, Ky., with Mr. George W. Fuller in charge. Mr. Ful ler's report on these investigations (see bibliog raphy) marked an era in water purification. It showed that a water as turbid as the Ohio, and with the large numher of bacteria sometimes carried by that stream, could be rendered thor oughly acceptable by means of sedimentation, coagulation, and mechanical combined.
litox REmov.u. F4 accomplished most frequent 1?,y by simple ;1i:ration to precipitate the iron, fol lowed by filtration for its removal. If aeration is not sufficient to effeet precipitation a chemical may be emplyed. like milk of limo where the iron is in the form of a sulphate. The few iron removal plants built in the United States up to the middle of 1901 were located on or near the North Atlantic seacoast, to treat water from wells.
TER Ise has been employed but rarely in the Cnited States, and then chiefly for supplies to the boilers of manufacturing plants nr locomotive.. The pioneer water•softening and one that is still largely used, was invented and patented by Prof. Thomas ('lark.
of Aberdeen. Scot land. about 1841. In the simplest form of Ibis lime water, or of is thoroughly inixral with the water to be treated. After twelve to twenty-four hours' subsidence the water is so drawn off as to leave the precipitate behind. :Nlodifications of the Clark system include a variety of settling and filtering devices. The process as described will remove only temporary hardness, or car bonate of lime or magnesia. Permanent hard ness, caused by the sulphates of lime and mag nesia, may be removed or reduced by using car bonate of soda as a precipitate, but the process is too expensive for general use.