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can also be beneficial to include pretreatment to remove key foulants. Various
biological treatment processes have been assessed for this duty, and have proved
to be very effective in removing low molar mass organic substances from the feed
water (Pauly, 2000; Tardif and Hall, 1997; Dufresne et al., 1998; Nuortila-
Jokinen et al., 1999; Suvilampi et al., 1999; Huuhilo et al., 2002). Foulants can
also be chemically bonded to form flocs through the addition of flocculating
chemicals, such as retention aids, fixatives and coagulants, thus preventing
them from interacting with the membrane (Nuortila-Jokinen et al., 1998). In
addition, ozonation (Nuortila-Jokinen and Nystrom, 2001) and electrodialysis
(Geraldes and de Pinho, 1995) have also been trialled.

3.2.6 Conclusions

The pulp and paper industry is a complex one with many different kinds of mills,
products and processes. Effluents therefore vary significantly in quality
depending on the process from which they originate. Due to this complexity
the requirements of water and effluent treatment at the different points of the
manufacturing process vary significantly. However, it is evident that there is a
great demand for an effective separation process, not the least due to the
increasing rigour of environmental legislation and its enforcement.
Membrane technologies have been demonstrated as being appropriate for
many water recycling duties within the pulp and paper industry. Existing
treatment schemes for concentration and fractionation of spent sulphite liquor,
deresination and bleaching effluent treatment by ultrafiltration include both
conventional tubular modules and high-shear systems. Membranes are
particularly advantageous when recovery of both chemical reagents and
clarified water is possible. It is likely that future membrane materials and modules
tolerant of temperatures close to 100°C and providing high fluxes with low fouling
propensity will be developed, and that the ongoing downward pressure on
membrane costs will continue to increase the economic competitiveness of this
technology for water recycling applications within the industry.

Acknowledgements
The authors wish to thank the Academy of Finland for financial support.
Colleagues at the Laboratory of Membrane Technology and Technical Polymer
Chemistry at Lappeenranta University of Technology are warmly thanked for
their co-operation over the years. Membrane and module as well as chemical
manufacturers are acknowledged for kindly giving us their products to test.

References
Afonso, M.D. and de Pinho, M.N. (1991). Membrane separation processes in pulp
and paper production. Filtration Sep., 28,42-44.