These tests were made by the author of a set of Jewell filters at Lorain, Ohio. The filters were six in number, each 17 feet in diameter, having an effective filtering area of 226 square feet each, or 1356 square feet in all. The construction of the filters was in all respects similar to the Jewell filter used at Louisville. The raw water was from Lake Erie, and during the examination was always comparatively clear, but contained considerable numbers of bacteria. The problem was thus entirely one of bacterial efficiency. The question of clarification hardly presented itself. Although the water became turbid at times it did not approach in muddiness the condition of the Ohio River water, and an amount of coagulant sufficient for a tolerable bacterial efficiency in all cases was more than sufficient for clarification.
A summary of the results obtained is as follows:
| Week Ending 6:00 P.M. | Average Rate of Filtration, Gallons per Sq. Ft. Min. | Sulphate of Alumina, Grains per Gallon. | Bacteria in Lake Water. | Bacteria in Effluent. | Bacterial Efficiency per cent. |
|---|---|---|---|---|---|
| June 19 | 1.06 | 2.58 | 1441 | 16 | 98.9 |
| 26 | 1.10 | 2.50 | 385 | 6 | 98.4 |
| July 3 | 1.11 | 2.27 | 367 | 9 | 97.5 |
| 10 | 1.28 | 1.07 | 154 | 14 | 90.9 |
| 17 | 1.14 | 0.94 | 189 | 26 | 86.3 |
| Average | 1.14 | 1.83 | 507 | 14 | 96.4 |
| The average bacterial efficiency was 96.4 per cent with 1.83 grains ofsulphate of alumina per gallon. | |||||
PITTSBURG EXPERIMENTS.[42]
The Pittsburg experiments were inaugurated by the Pittsburg Filtration Commission. The operation of the filters extended from January to August, 1898. A Jewell and a Warren filter were used similar in design to those used at Louisville. The raw water contained large numbers of bacteria, and was also often very turbid, although less turbid than at Louisville. At times more coagulant was necessary for clarification than was required for bacterial efficiency; while as a rule more was required for satisfactory bacterial purification than was necessary for clarification. The opportunities were therefore favorable for the study of both of these conditions. The amount of coagulant necessary for clarification has been mentioned in connection with coagulation.
The results secured upon the relation of the quantity of coagulant to the number of bacteria in the effluent were more complete than any other experiments available, and are therefore here reproduced from the Pittsburg report nearly in full.
It was found that the amount of sulphate of alumina employed was more important than any other factor in determining the bacterial efficiency, and special experiments were made to establish the effect of more and of less coagulant than used in the ordinary work. These experiments were made upon the Warren filter during May, and with the Jewell filter during June. The monthly averages for these months are thus abnormal and are not to be considered. The remaining six months for each filter may be taken as normal and as representing approximately the work of these filters under ordinary careful working conditions.
During the six months when the Warren filter was in normal order the raw water contained 11,531 bacteria and the effluent 201, the average bacterial efficiency being 98.26 per cent. The bacterial efficiency was very constant, ranging only, by months, from 97.48 to 98.96 per cent. During the same period a sand filter receiving the same water yielded an effluent having an average of 105 bacteria per cubic centimeter.
The Jewell filter, for the six months in which it was in normal order, received raw water containing an average of 11,481 bacteria and yielded an effluent containing an average of 293, the bacterial efficiency being 97.45 per cent, and ranging, in different months, from 93.23 to 98.61 per cent.