Ultimate Disposal of Sewage
Sludge by Wet Oxidation
E. Hurwttz, Director of Laboratories
and
W. A. Dundas, General Superintendent
The Metropolitan Sanitary District of Greater Chicago
Chicago, Illinois
Sewage treatment has as its objective the separation of suspended
solids from the waste water by mechanical means and the conversion
of the colloidal and dissolved substances, by biological action, into
suspended solids that can be readily separated from the liquid phase.
The art has developed to a degree that effluent standards can be
achieved readily. However, the treatment and disposal of the accumulated solids, in order to reduce or overcome their potential health hazard
and to decrease their volume for ultimate disposal, is a problem of
major proportions.
METHODS OF SLUDGE DISPOSAL
The most widely used method for disposal of the organic solids
that are separated from sewage is by anaerobic fermentation in sewage
digestion tanks followed by partial dewatering of the digested material
on sludge drying beds or by storing in sludge lagoons. This method is
used extensively where sufficient low cost land is available to provide
area for sand beds or lagoons. The dried sludge must be removed to a
point of final disposal. In some communities it may be sold as a soil
conditioner. Usually the financial return from such an operation is
small and does not result in any substantial reduction in the cost of
sludge handling.
Another method for disposing of sewage solids is by partial dewatering on vacuum filters to convert the raw or digested sludge into a
more easily handled form for either disposal on land, further drying
for fertilizer (soil conditioner), or incineration. To accomplish this,
the raw or digested sludges are generally elutriated and treated with
ferric chloride or treated with lime and ferric chloride without elutria-
tion to condition the sludge to a structure which permits more rapid
removal of the water when it is subjected to vacuum filtration. Operating costs and  capital  investment  for  this method  are  usually  higher
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