736 MUNICIPAL WASTEWATER
The Imhoff Tank has not been discussed earlier because
it is similar in many respects to the septic tank. Use is gener-
ally confined to small communities and isolated installations.
Operation is a combination of sedimentation and anaerobic
digestion. This tank was invented by Karl Imhoff, who first
used them in the Essen District in Germany in 1907. The
tank is composed of two chambers, one above the other.
Surface configuration may be circular, square or rectangular.
Depth is 25′ to 35′.
Sewage flows through the upper chamber, at a low veloc-
ity (about 1 fps). Solids settle out and slide through a slot
into the bottom chamber. Detention period is about 2 hours.
Solids accumulating in the bottom, or digestion, chamber
have an initial water content of 85 to 95%. After proper diges-
tion of about 60 days the water content is reduced to about
50% and the volume is greatly reduced. Gases produced
during digestion are vented to the atmosphere by gas vents
located at the tank sides. Solids buoyed up by gas are pre-
vented from escaping to the upper tank by deflector plates.
Attempts were made to hasten digestion by heating the
lower compartment but were of limited success due to over-
turning of the tank contents.
Some rectangular tanks are arranged so that the direction
of flow can be reversed, with outlets becoming inlets and
vice versa.
In recent years manufacturers of waste treatment equip-
ment have endeavoured to supply complete treatment plants
for small communities or developments and isolated instal-
lations. Basically, these plants, called package plants, supply
primary treatment and sometimes some biological treatment
on a small scale without requiring extensive operating super-
vision. It is felt that such treatment is to be preferred to septic
tanks or only primary treatment (Imhoff Tanks, for example),
but such installations are not the ultimate solution.REFERENCES- Anderson, E. and W.T. Lockett, J. Soc. Chem. Ind. London , 33 , 523,
1914. - Bewtra, J.K., Biological Treatment of Wastewater, Encyclopedia of Envi-
ronmental Science and Engineering , 4 th Ed., Vol. 1, Gordon and Breach,
Inc., New York. 1998. - Bewtra, J.K. and H.I. Ali, Physical and Chemical Treatment of Wastewa-
ters, Encyclopedia of Environmental Science and Engineering , 4^ th^ Ed.,
Vol. 2, Gordon and Breach, Inc., New York. 1998. - Bewtra, J.K., Recent Advances in Water-pollution-control Technology.
Advances in Environmental Science and Engineering , 1 , Gordon and
Breach, New York, 1979.
5. Camp, T.R., Trans. ASCE , 3 , p. 895, 1942.
6. Cecil, L.K., Water reuse, Encyclopedia of Environmental Science and
Engineering , 2 , Gordon and Breach, Inc., New York, 1983.
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8. Disposal of Municipal Sewage. House Report No. 20 12th Report
by Committee on Government Operation, House of Representatives,
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9. Dobbins, W.E., J. of the Sanitary Engineering Division, ASCE , 90 , No.
SA 3, Proc. Paper 3949, June 1964.
10. Eckenfelder, W.W. and D.J. O’Connor, Biological Waste Treatment ,
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11. Fair, G.M., J.C. Geyer, and D.A. Okun, Water and Waste Water Engi-
neering , 1 and 2 , John Wiley and Sons Inc., New York, N. Y., 1968.
12. Guttman, H.N., Microbiology, Encyclopedia of Environmental Science
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13. Imhoff, K., Taschenbuch der Stadtentwässerung , R. Oldenbourg Verlag,
Munich, 1960.
14. Imholff, K. and G.M. Fair, Sewage Treatment 2nd Ed., John Wiley and
Sons, Inc., New York, N.Y., 1956.
15. McKinney, R.E., Microbiology for Sanitary Engineers , McGraw-Hill
Book Co., New York, N. Y., 1962.
16. Nolte, W.F., Effects of elevated pressure on secondary treatment of
wastewater, Advances in Environmental Science and Engineering , 4 ,
Gordon and Breach, New York, 1981.
17. Pfafflin, J.R., Water: Sewage, The Encyclopedia of Chemical Technol-
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18. Pfafflin, J.R., Water: Reuse, The Encyclopedia of Chemical Technol-
ogy , Interscience Publishers, Inc., New York, N.Y., 1981.
19. Phelps, E.B., Stream Sanitation , John Wiley and Sons, Inc., New York,
N.Y., 1944.
20. Pollock, D.C. and M.A. Wilson, Development of Deep Shaft Effluent
Treatment Process in North America , Second World Congress of Chem-
ical Engineering, Montreal, 1981.
21. Qasim, S.R., Wastewater Treatment Plants—Planning, Design and
Operation, Holt, Rinehart and Winston, New York, 1985.
22. Salvato, J., Environmental Sanitation , 2nd Ed., John Wiley and Sons,
Inc., New York, N.Y., 1972.
23. Sawyer, C.N. and P.L. McCarty, Chemistry for Sanitary Engineers ,
2nd Ed., McGraw-Hill Book Co., New York, N.Y., 1967.
24. Standard Methods for the Examination of Water and Waste water ,
17th Ed., APHA, 1990.
25. Streeter, H.W. and E.B. Phelps. A study of the pollution and natural
purification of the Ohio river. Public Health Bulletin 146, US Public
Health Service, Washington, D.C., 1925.
26. UK Patent No. 2,128,980.
27. US Patent No. 4,464,257.
28. US Patent No. 4,500,428.
JAMES R. PFAFFLIN
Gillette, N.J.CAMERON MACINNIS
University of Windsor.MUNICIPAL WATER REUSE: see WATER REUSE
MUNICIPAL WATER SUPPLY: see WATER TREATMENTC013_007_r03.indd 736C013_007_r03.indd 736 11/18/2005 10:43:42 AM11/18/2005 10:43:42 AM