CLEAR WATER FROM THE MISSISSIPPI.
MR. CHARLES E. CUTTER in a long communication writes of the filtration system at Davenport, Ia, by means of which the muddy water of the Mississippi is rendered clear and potable. In that city every drop of water that is distributed through the mains is filtered and supplied to the citizens by the Davenport Water company at no higher price than is paid elsewhere for water that is by no means wholesome.
For the excellent system in vogue at Davenport the city is indebted to James P. Donahue, son of Hon. Michael Donahue, founder of the water works, secretary of the Davenport Water company. Mr. Donahue, being determined that the water should be improved in quality, studied the subject of mechanical filtration at home and abroad—his foreign investigations being conducted in some of the largest cities in Europe. The outcome was the adoption of a costly system of filtration. The plant is said to be fifty per cent, larger than any other in use and consists of ten double filter shells,each seven and one-half feet in diameter and thirty-two feet long. The filter shells are built of steel, five-eighths of an inch thick, with a tensile strength of 60,000 pounds, and have stood a steady proof test of 200 pounds to the square inch. These filters are so arranged that any one of them can be operated separately or the whole battery collectively. The tanks are about three-quarters full of white sand, amounting in all to about thirty carloads, brought at first from Horn island, in the gulf of Mexico. The supply for renewing is now secured from Fontenac, Minn. The peculiar nature of this sand is that each grain is of almost even texture and a perfect crystal. Ordinary river or building sand, being porous, would tend to make it unfit for filtering purposes. When water contains microbes sometimes so infinitesimally small that it would require the most powerful magnifying glasses to detect them,these might readily lodge themselves in the pores of the porous sand and die and rot, thereby rendering the filters disease-producers. For this good and sufficient reason, then, is the sharp, solid and anti-porous crystal sand necessary, and an all important factor forgood filtration.
The water is forced by the pumps through twentyinch faed mains into the filters, passing downwards through five feet of sand, thence through a peculiarly shaped screen,made of extremely fine silts sawed through cylinders of heavy, seamless tubes, made of combination metal, thence out into the mains, to the city, and the reservoir to the hills. This process renders the river water, even at the highest floods, as bright, clear, and sparkling as spring water. Sediment and other matter which is removed from the water is retained for a time in the filter on top of the sand. This deposit is quickly and economically removed at Davenport, bj’ applying thousands of fine, powerful jets of water directly to the place where the dirt accumulates, washing the sand at the same time by reversing the current of water from the bottom of the bed, some feet below the surface. This is accomplished by supplying the water to the filter through horizontal perforated arms attached to a central vertical pipe with a piston. By admitting the water pressure from the mains to this piston, the Urms are forced downwards and back through the filtering material, applying the washing jets, each three-sixteenths of an inch [in diameter and under eighty pounds pressure, to every grain of sand in the mass, throwing the whole into violent agitation, thus scouring the sand completely clean and washing the dirt and sediment accumulated off through a drain into the river again below the works. The thoroughness of the work and the rapidity of the operation are such that it requires less than five minutes to wash a filter, and the mechanism is so simple that there is scarcely any liability of its getting out of order.
The thorough sterilization of the filter and sand bed, and freeing it from all microscopic algfe and infusoria-albuminoids and other impurities is accomplished by draining the filters frequently, and then turning into them powerful jets of superheated steam, which in a remarkably short time kills all animal or vegetable life therein.
Coagulation is accomplished in the Davenport system by means of using about three-eighths of a grain of sulphate of alumina per gallon of water, and it has been proven after careful and practical tests, that from seventy to ninety per cent, of the alumina in solution injected into the water before filtration is absorl>ed by the matter in suspension, forming a coagulated mass on top of the sand bed, which is washed out when cleansing the filters, leaving an amount too infinitesimally small to be detected by chemical analysis.
Pumping station No. 1, on the Mississippi river, about one mile above the Government bridge, conuecting Davenport with Hock Island arsenal and the Illinois side of the river, contains the filter plant. The filters and pumps are in a substantial brick building, 2(51 feet long by (58 wide. The pumping machinery Is very complete, consisting of a high-duty compound, condensing,duplex Worthington pumping engine, capable of deli veringG,000,000 gallons of water j>er day, and a 5,000,000 gallon set of pumps of the Clapp and Jones type. In addition to these there was added a short time ago a Holly improved Gaskill, compound, condensing engine of 5,000,000 gallons capacity daily. Water from the river is delivered into the pump wells through a tunnel built under the bed of the river, out into the middle of the stream. The pump wells, built of heavy masonry, are thirty feat deep. From these wells, after the water has been well screened, the pumps of station No. 1 take the water, mixed with a solution of alumina, and deliver it through the filters, under direct pressure, to the city mains and the reservoir* This reservoir is at pumping station No. 2, and has a capacity of 5,000,000 gallons. The water from the reservoir supplies that portion of the city on the. bluffs lying above Sixth street. At this station the pumping machinery consists of a vertical set of compound Clapp and Jones pumps, having a daily capacity of 5,000,000 gallons, and a 2,500,000 gallon set. of duplex Gordon steam pumps. The pressure obtained by t he pumps at the two stations is so great— being strong enough to carry a stream over a tivestory building—that no fire engines are necessary. Mr. C C. Schmidt, who has been with the Davenport water company for many years, is the chief engineer, and has entire charge of the filter plant and two pumping stations,