Section Seven
INDUSTRIAL WASTES
F. PULP AND PAPER MILL WASTES
75    TOTAL CLOSING OF PAPER MILLS WITH RECLAMATION
AND DEINKING INSTALLATIONS
Milos Krofta, President
Krofta Engineering Corporation
Lenox, Massachusetts 01240
Lawrence K. Wang, Director & Professor
Lenox Institute for Research
Lenox, Massachusetts 01240
INTRODUCTION
Wastepaper is recycled as pulp for reproduction of papers or boards. The pulp containing secondary fibers needs to be purified in a deinking installation. A total closed water system has now been
developed for water reclamation in deinking installations. The pulp with inks is first processed with a
dispersed air flotation cell (Foamer) and then a washing unit (stock washer). The wastewater is
clarified by a dissolved air flotation cell (Supracell) for water reclamation. A fractionator (spray
filter) is additionally used for recovery of long fibers from washing water. The sludge is thickened on a
thickener (twin wirepress). The newly developed water reclamation and deinking systems in Europe
are highly efficient and cost-effective. For academic and engineering contributions, special emphasis
is placed on the design of individual treatment units and the entire deinking/reclamation system.
Several case histories are introduced.
HISTORICAL DEVELOPMENTS
Since 1965 Krofta Engineering Corporation and Lenox Institute for Research, both in Lenox, MA,
USA, have been developing equipment for reuse of wastepaper and water reclamation in deinking
processes.
High raw material prices, combined with high energy costs and progressively stronger effluent
pollution control are making wastepaper deinking always more economically feasible and closing of
the deinking water systems imperative.
Until recently wastepaper was used exclusively for the low-grade boards or for multiple layer board
as internal gray filler. In the near future, it is expected that more and more wastepaper recovered from
municipal solid waste treatment plants will be used for this purpose and more printed wastepaper will
increase in value as a raw material for better grades of paper, if the deinking technology is sufficiently
developed.
Presently the bulk of wastepaper deinking is concentrated on newsprint waste deinking. The reasons are: 1) the daily collection of overissues provides for a steady raw material flow; and 2) the
requirements for degree of brightness for newsprint is not too high.
The next group of present wastepaper deinking is considerably smaller and used for the production
of tissue papers. The general trend toward always higher and higher brightness and softness of tissue
paper places considerable demand for a continuous improvement of the deinking technology.
With considerable distance follows the deinking of printed books with a very high basic value of the
original paper fiber but with also very high demand on cleanliness and brightness.
For decades two principal deinking systems have been competing: 1) flotation deinking, extracting
ink by foam generated by a dispersed air flotation cell (mineral filler and paper fines are mainly
recovered therefore the yield is high but the physical strength of the deinked stock is poor); and 2)
43rd Purdue Industrial Waste Conference Proceedings, © 1989 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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