| TABLE III. | ||
|---|---|---|
| RATE OF SEWAGE TREATMENT. | ||
| System. | Location. | Sewage treated in gallons per acre per day. |
| IRRIGATION. | ||
| Berlin, Germany. | 18,000. | |
| Manchester, Eng.—Estimated but not constructed. | 18,500. | |
| INTERMITTENT DOWNWARD FILTRATION. | ||
| Framingham, Mass. | 19,000. | |
| Leicester, Mass. | 38,750. | |
| Brockton, Mass. | 44,000. | |
| Marlborough, Mass. | 54,000. | |
| Gardner, Mass. | 140,000. | |
| Mendota, Ills. | 184,000. | |
| Worcester,[[1]] Mass. | 322,000. | |
| Worcester,[[1]] Mass. (Fletcher’s estimate). | 500,000. | |
| Madison,[[1]] Wis. | 8,000,000. | |
| CONTACT BEDS. | ||
| Manchester, Eng. (crude sewage) | 500,000. | |
| Manchester,[[1]] Eng. | 700,000. | |
| Manchester, Eng. (storm water sewage) | 2,500,000. | |
[1]. Secondary filtration.
Table III shows the capacity of representative plants. Best authorities consider 100,000 gallons per acre per day to be the maximum rate permissible under the best conditions for the treatment of crude sewage by the intermittent downward filtration system. With unfavorable conditions the quantity of sewage should be limited to as low as 20,000 gallons. Wherever too large a dose is applied to the bed the sewage is not properly purified and the beds soon become clogged up and unfit for further use.
When the beds are used for secondary purification, 750,000 gallons may be treated per acre per day.
The results of extensive experiments made at Manchester, England in 1898 and 1899 show that by means of contact beds crude sewage may be treated at the rate of 500,000 gallons per acre per day. When the beds are used for secondary purification, 750,000 gallons may be successfully treated, and storm water sewage treated at the rate of 2,500,000 gallons per acre per day.
The capacity of the chemical precipitation plant at Madison, Wisconsin is 68 percent of the daily flow, which in 1899 was estimated at 300,000.
The company that built the plant agreed that the plant should have a daily capacity of 1,200,000 for each and every day in the year. This shows the estimated capacity of the tank to be 28 percent.
At Worcester, one of the best examples of this process is in operation. The size of the tanks is equal to 28 percent of the total flow of 17.1 million gallons per day of which 10.1 million gallons is the out flow from a comparatively clear pond. If the actual amount of sewage is considered the tanks have a capacity of 65 percent of the total flow.
Rafter and Baker in their discussion of the size of tanks recommends that the total capacity should be nearly 50 percent of the average daily flow.
The two typical types of septic tanks are those at Exeter, England and at Champaign Illinois. The first has a cubic capacity of 93 percent of the total daily flow, while the second has a capacity of 7.5 percent of the daily flow.