Factors Involved in the Drainage
of White-Water Sludge
John F. Vogler and Willem Rudolfs
Rutgers University
New Brunswick, New Jersey
For several years studies have been in progress at Rutgers Univer¬
sity on the treatment and disposal of white-water wastes from paper
and paperboard mills. These investigations have been concerned pri¬
marily with evaluation of the characteristics and behavior of white
water, the clarification, coagulation, and digestions of the wastes, and
studies on the dewatering of sludges produced by the clarification of
these wastes. One phase of the dewatering studies dealt with an
investigation of the factors involved in the drainage of white-water
sludge.
The clarification of white water from a paper or board mill poses
the problems of reuse or disposal of the large volumes of hydrous
sludge produced. Much work has been done on the possibility of by¬
product or usable fiber recovery from such sludges, but in many in¬
stances none or only part of the sludge formed can be incorporated
into the product. This is due mainly to the variable compositon of such
sludges, to the cost of recovery, and to impurities in the recovered
materials. In such cases, disposal is the only solution, and the problem
of obtaining these sludges in a workable dry state is presented.
Nature of Boardmill Sludge
The general characteristics of white water sludge are dependent
upon the type of raw materials used, mill operation, and the method
of save-all and waste clarification used. The solids consist of fiber,
usually of small particle size, filler, sizing, and large amounts of im¬
purities and cellulose debris, especially in the case of boardmill sludge.
The coagulation of the impurities and debris in the dispersed phase
forms hydrogels with large amounts of bound water, or water of inhi¬
bition. Volatile solids constitute 70 to 80 percent of these sludge
solids, and this fraction may be considered as apparent fiber. The pH
of the sludge usually ranges from 5 to 7 as a result of the alum used
in the papermaking process.
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