Rock Island Water Works and Filter Plant

Rock Island Water Works and Filter Plant

GENERAL ARTICLES

One of the greatest assets of the city of Rock Island, Ill., is its water works system, producing as it does a supply of water which by repeated tests by the city, state and federal authorities has been shown to be pure and entirely safe for use. Rock Island has had its municipal water works since 1872. An ordinance passed in 1871 created the water works department of that city and provided for the establishment of a commission to be composed of the mayor, three aldermen and three citizens, and prescribed the duties of the commission. The commission was authorized to proceed with the establishment of a pumping station and construction of such a plant “as may be necessary for supplying said city with pure and wholesome water.” Another ordinance adopted the same year vacated a plot near what is now the center of the city and on the Mississippi river and provided for the construction of a complete water plant. Because of contamination of the water above, there was agitation in 1881 to remove the plant farther up stream and, while this proposition was defeated at a special election, a gift of $25,000 from a resident of that city made it possible. In 1891 another donation made possible the installation of gravity sand filters. This system, under the imposed conditions, was never a success, and the installation proved a source of great expense to the city. After a lengthy investigation, it was decided to install mechanical filters. This improvement was completed in 1912 at a cost of about $70,000. From the first they proved highly successful as frequent tests have shown. The filter plant, as described by R. W. Sharp, superintendent of the water department, is as follows: “The rapid sand filter plant at Rock Island was built in 1910-11. It is the conventional type with a capacity of six million gallons per twenty-four hours, having two settling basins which have a coagulation period of from four to twelve hours when the plant is operated at full capacity. This six million gallon plant is built within one of the old one million gallon slow sand filters of which there were three. The coagulant is applied to the raw water at the inlet of the basins, and after passing through the basin the treated water is conducted to the filters by a thirty-inch conduit into which the bleach is applied about twenty-five feet from the filters. There are six filter units, each of which is 24 feet by 17 feet, a filtering area of 365 square feet, equipped with separate brass air manifolds so that, if desired, the air and water may be applied at the same time during the washing period. Each filter has three concrete wash troughs giving a maximum lateral flow of the soiled wash water of two feet from any part of the filter to the weir of the troughs. The water collecting system and the under drain piping of the filters with the exception of the strainers, are entirely of cast iron, embedded in concrete with brass strainers set at six-inch centers. Each filter is equipped with recording loss of head gauges, outlet rate-controllers, and hydraulically operated valves, while all pumps and other machinery are operated by electricity. According to the specifications, the plant was required to produce a filtrate having less than one hundred bacteria per cc., except when the raw water contained over three thousand bacteria per cc., then the reduction should be at least 97 per cent. The wash water was not to exceed 5 per cent, of the amount of water filtered. The test for this guarantee was made from May 3tst to June 30th, 1911. The results were as follows: The average bacterial count for the raw water was 1875 per cc. with a maximum of 3.150 and a minimum of 1,075. The average bacterial count for the settled water as it passed to the filters, was 110 per cc. with a maximum of 450 and a minimum of 32 per cc. The average bacterial count for the filtered water was 27 per cc, with a maximum of 80 and a minimum of 6 per cc. Hence the average removal between the raw and filtered water was 98 per cent. The average color was reduced from 75 to 20 parts per million, the average alkalinity was reduced from 96 to 67 parts per million, while the removal of the turbidity was complete. In the raw water, gas formers were found in all but three of the one cc. samples. In the filtered water all but one of the samples were negative, while the bleach was being used ; but out of 20 samples that were taken after the bleach was discontinued, 9 showed gas formers. The average amount of wash water used during the test was 2.4 per cent. of the amount filtered, with a maximum of 4 per cent, and a minimum of .8 per cent. Calculations of the amount of wash water used were made by measuring the vertical rise in each filter during washing, the sewer outlet valve being closed. During the year 1911, the average colony count in the raw water was 6,448 per cc. with 84 per cent, of the samples showing gas formers. In the filtrate, the average colony count was 168 per cc. with 9 per cent, of the samples showing gas formers. The color was reduced from an average of 62 to 24 parts per million. During the year of 1912 the average colony count in the raw water was 7,660 per cc. with 82 per cent, of the samples showing gas formers. In the filtrate the average colony count was 67 per cc. with 10 per cent of the samples showing gas formers. The color was reduced from an average of 75 to 15 parts per million. During this time, alum and bleach were not used in parallel at all times, but were alternated from time to time to check up the different modes of operating the plant with the various changes in the raw water. About a month after the test on the plant, considerable difficulty was experienced with the coagulant feed pipes, which are about 350 feet in length. These were replaced with fibre pipe and rubber hose on July 8th, 1912, and have given much better results up to the present time.”

OPERATING ROOM ROCK ISLAND FILTER PLANT.FILTER HOUSE, ROCK ISLAND, ILL.CHEMICAL SOLUTION TANKS, ROCK ISLAND FILTER PLANT.PIPE GALLERY, ROCK ISLAND FILTER PLANT.

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