OPERATION OF THE ITHACA FILTRATION PLANT
In a report made by Henry N. Ogden, C. E., Professor of Sanitary Engineering, College of Civil Engineering, Cornell University, to the Board of Public Works of Ithaca, N. Y., on the operation of the filtration plant at Ithaca, N. Y., during the year ending December 1, 1916, he renews a suggestion made a year before that the outside walls above the filters be waterproofed to protect the walls and to prevent the infiltration of water from the outside whenever it rains. The average daily amount of water filtered throughout the year was 2,299,420 gallons, as compared with 2,282,000 gallons in 1915. The average amount of water used by the MorganSmith wheel at the Van Natta pumping station as measured by the Venturi meter at the filter plant was 3,135,097 gallons, or nearly a million gallons (835,677 gallons) more than that used by the city for domestic purposes. Professor Ogden states that to show the variations in the daily demands on the filter plant, a diagram has been prepared Beginning with April 5, 1914, when the direction of the filter plant was placed in his hands, the diagram shows the amount of water measured by the circular weir delivering raw water to the plant and the relation to the seasons and the days of the week is also indicated. The effect of University vacations and of Sundays is plainly marked as well as the small effect of fires. The water wheel and generator, installed for lighting the filter plant and the pumping station adjoining, has continued to give good service and utilizes power which would otherwise be wasted. Relative to the settling basins, Professor Ogden says: “The settling basins have been cleaned three times during the year, January 24, May 24 and September 28. The comparatively dry summer made less demands on the capacity of the basins and although in 1915 the basins were cleaned in July and in August, in 1916, no such frequent cleaning seemed needed. The daily determination of turbidity have teen continued. The average for this past year has been 95, as compared with an average of 167 (corrected to 12 months) for 1915. This difference in the quality of the raw water is reflected in the amount of coagulant used as will be seen in the next paragraph. After the middle of June the turbidity was continually low, in fact so low that the water could have been applied directly to the filters without intermediate sedimentation. The average daily amount of sulph of aluminum used was 346 pounds and the total amount used during the year has been 126,234 pounds, or about 63 tons, which is 14 tons less than in 1915. The average amount may also he expressed as 150 pounds per million gallons of water treated, less by 35 pounds than last year and being almost exactly one grain per gallon. The maximum amount used was on March 31, when the turbidity was the highest (1,000) and when 1,000 pounds of the coagulant was used, while from the middle of June to the end of September the amount used was continuously about 200 pounds or one bag a day. The value of the large storage reservoir above the Potter’s Falls Dam is probably of great value in neutralizing the effect of short rains and to keep this value at a maximum. The clcan-out valve in this dam should te opened at least once a year and the material settled around the intake well scoured out. The dry feed apparatus continues to give very satisfactory service. Professor Ogden continues: “Due to the cost of the chloride of lime, used heretofore for final disinfection, it seemed best to you, early in the year to substitute treatment by liquid chlorine, using the apparatus made by Wallace and Tirman. This was set up on February 10, and has been in continuous use since that date. It is a very great improvement over the chloride of lime solution and is most effective in eliminating any bacteria that mav have escaped the filters. Eight cylinder of 100 pounds each of the chlorine have been used since February 16, so that each has lasted on the average 35 days. The amount of liquid chlorine used has been from 800 to 850 pounds and the water treated has been 651 million gallons or 1.1 pounds per million gallons. No variation in the rate is made since the filtered water to which the chemical is added is of uniform character. The number of bacteria in the raw water from day to day has been regularly determined throughout the year. The average bacteria counts in raw water, gelatine count, were: December, 1,052; January, 2,212; February, 583; March, 2,180; April, 2,317; May, 1,549; June, 1,643; July, 281; August, 207; September, 271; October, 574; November, 781. The average number of bacteria in the filtered and treated water, gelatine count, was: December, 1.9; January, 2.7; February, 2.7; February, 2.7; March, 3.5; April, 2.9; May, 4.1; June, 3.2; July, 2.1; August, 2.5; September, 3.6; October, 3.1; November, 3.7. The average per cent, reduction for each month has been computed with the following results: December, 99.2; January, 99.8; February, 99.2; March, 99.8; April, 99.8; May, 99.3; June, 99.6; July, 99.3; August, 99.0; September, 98.7; October, 99.2; November, 99.5. The average of the year is thus 99.27. Counts have also been regularly made on agar at 37°C and have shown equally good results. Tests for gas producers in lactose broth b le as an indicator of the possible presence of intestinal organisms have been made daily in both 10 c. c. and in 1 c. c. sample of the filtered water and the results have always been negative, that is, the water supplied to the city has invariably been free from disease producing organisms, so far as this standard test can guarantee such a condition. In the raw water, on the other hand, 1 c. c samples have with equal regularity always shown the presence of these germs. The efficiency of the filtering process is thus demonstrated and the purity of the city water as supplied for drinking demonstrated, in so far as scientific analysis can demonstrate it. Tests for alkalinity have been regularly made in order to make sure that the coagulant supplied would be properly broken up and leave no free alum in the water. Fortunately, the water of Six Mile Creek carries at most times a large excess of carbonates and sulphates, so necessary for the coagulating pfocess used in filtration, the amount ranging from 50 to 100 parts per million, while even with the greatest turbidity, not more than 25 parts are required.