TOWARDS ZERO-EFFLUENT PULP AND PAPER PRODUCTION: THE PIVOTAL ROLE OF TOTALLY CHLORINE FREE BLEACHING

The world pulp and paper industry continues to expand production and increasingly, plants are being built in newly industrialised countries. The dominant process is the kraft or sulphate process. Historically, substantial pollution problems have been associated with pulp manufacturing operations. Following the recognition of large scale environmental contamination by organochlorines due to their formation in bleach plants, the industry implemented a number of process internal changes and continued to develop process external treatment processes. The bleach plant of kraft mills generates a substantial proportion of the total process effluents. The introduction of extended delignification and oxygen delignification can substantially reduce the quantities of lignin entering the bleach plant. Residues from oxygen delignification can be cycled to the recovery process. Overall, this reduces the demand for bleaching agents and hence reduces the generation of organochlorines. Together with substitution of elemental chlorine (Cl2) with chlorine dioxide, these systems have substantially reduced levels of AOX being discharged from bleach kraft mills. Organochlorines, however, have not been eliminated from discharges, merely reduced. Swedish research has shown detectable levels of toxicologically chlorinated dioxins and dibenzofurans in the effluents from mills that use chlorine dioxide; so-called elemental chlorine free (ECF) mills. This stems from the fact that ECF processes are not free of elemental chlorine. Commercial chlorine dioxid