348 
Theodore Sedgwick Johnson 
Philadelphia experiments show 0.9 cubic yard per million gal- 
lon, or at a rate of 75 gallons per capita, a deposition of sludge 
at the rate of 0.002 cubic foot per capita per day. 
Chicago experiments show 2 cubic yards during the summer 
and fall of 1910 and 0.93 cubic yards per 1,000,000 gallons for 
five months. 
At Recklinghausen, 1.65 cubic yards, at Bochum, 2.1 and at 
Essen-N-W, 1.39. The last three values deal, of course, with 
strong sewage. Allen advises a sludge storage capacity to pro- 
vide for a mean between the amount of fresh sludge and the final 
volume of treated Imhoff tank sludge. Allen states by formula 
the capacity C = 5250 PD, where P is population, C capacity 
in cubic feet and D the day’s retention of sludge. 
Imhoff gives for Bochum (combined system) a value of 0.007 
cubic foot per capita daily — the figure used in the Winters, Cal- 
ifornia, installation, and says it would be half that much for sep- 
arate system, or 0.0035. On these assumptions, John H. Gregory, 
for the Metropolitan Sewerage Commission of New York, pre- 
pared a table,^ which gives for a daily sewage flow of 75 gallons 
per capita a volume of sludge of 1.7 cubic yards per 1,000,000 
gallons. 
Tabulating the various estimates: 
Cubic feet per 
capita daily 
Winters, California 0.007 
Philadelphia, Pennsylvania 0.002 
Chicago, Illinois 0.002 
Recklinghausen, Germany 0.0036 
Bochum 0.0045 
Essen, N-W 0.0031 
Gregory (Metropolitan Sewage Commission) 0.0038 
Pacific Flush Tank Company pamphlet 0.0033 
Allen, Hazen (Amer. C. E.’s Pocket Book) 0.0022 to 0.0044 
With these comparative figures before us, it seems reasonable 
to adopt a figure of 0.0035 cubic foot per capita daily, as the 
rate of deposition of sludge in the digestion chamber. 
3 Allen, Sewage Sludge Treatment in the United States, pp. 229. 
