Total Chlorine Free Bleaching Research Articles

Analysis of pitch deposits produced in Kraft pulp mills using a totally chlorine free bleaching sequence

Two organic deposits accumulated in a Kraft pulp mill during pulping of Eucalyptus globulus wood and throughout a TCF (totally chlorine free) bleaching sequence were characterized. One deposit was collected after cooking and an oxygen delignification stage while the other was collected after bleaching with hydrogen peroxide. The deposits were Soxhlet extracted with acetone, and the extracts redissolved in chloroform and subsequently analyzed by gas chromatography (GC) and GC–mass spectrometry (MS) using short and medium length high temperature capillary columns, respectively. On the other hand, the insoluble residues left after the acetone extraction were analyzed by Curie-point flash pyrolysis–GC–MS and by pyrolysis–methylation–GC–MS. The compounds identified in the deposits arise from the E. globulus wood lipophilic extractives that survive the pulping and bleaching processes. Triglycerides were completely hydrolyzed during the Kraft cooking and the fatty acids dissolved. Steroids (alcohols, hydrocarbons, ketones and esters) and waxes were the main components in the deposit collected after the oxygen delignification stage. After the bleaching with hydrogen peroxide, content of the waxes were reduced and fatty acids appeared. High amounts of fatty acids salts were also identified in the deposit collected after the oxygen stage, and in minor amounts in the deposit collected after hydrogen peroxide bleaching. In contrast, this deposit was mainly made up of high amounts of lignin-derived phenolic moieties.

Modulation of immune parameters of roach, Rutilus rutilus, exposed to untreated ECF and TCF bleached pulp effluents

The present study was designed to assess the effects of elemental chlorine free (ECF) and totally chlorine free (TCF) pulp and paper mill effluents on the immune defence of the roach ( Rutilus rutilus). Fish were exposed for 5 weeks to concentrations of 0, 0.6, 2, 6 and 20% of untreated effluents from ECF or TCF bleaching processes. In order to study the capability to respond to foreign antigens the fish were immunised with bovine γ-globulin (BGG) 3 weeks before sampling. The numbers of anti-BGG antibody-secreting cells and immunoglobulin-secreting cells in the spleen and blood, as well as the levels of the anti-BGG antibodies and concentrations of immunoglobulin in plasma and the proliferation of lymphocytes after mitogenic activation were determined. In addition, phagocytosis-related functions, respiratory burst activity and migration of leukocytes, were measured. Formation of specific anti-BGG antibody-secreting cells in the blood and immunoglobulin-secreting cells in the spleen and blood were suppressed in the fish exposed to a high concentration (20%) of ECF effluent. Similarly, the level of anti-BGG antibody and the stimulation indices of Concanavalin A-stimulated proliferation responses in vitro were lower in these fish. A decreased migration of granulocytes was observed in the fish exposed to 0.6–2% of ECF and TCF effluents. These results demonstrate that untreated ECF and TCF effluents significantly affected the immune parameters of the roach. Taken as a whole, fish exposed to TCF effluent showed less immunomodulation than those exposed to EFC effluent.

Anaerobic biodegradability and toxicity of wastewaters from chlorine and total chlorine-free bleaching of eucalyptus kraft pulps

Chlorine bleaching effluents are problematic for anaerobic wastewater treatment due to their high methanogenic toxicity and low biodegradability. Presently, alternative bleaching processes are being introduced, such as elemental chlorine-free (ECF) and total chlorine-free (TCF) bleaching. The methanogenic toxicity and anaerobic biodegradability of ECF and TCF bleaching effluents from oxygen-delignified eucalyptus Kraft pulp were compared with those of different chlorine bleaching sequences. The effluents from chlorine and ECF bleaching sequences had similar methanogenic toxicities, with 50% inhibiting concentrations (50%IC) of 0.65–1.48 g-COD/litre. Only the TCF bleaching effluent was distinctly less toxic, with a 50%IC of 2.3 g-COD/litre. The fact that the ECF bleaching effluent was not less toxic than that of chlorine bleaching, as well as the residual toxicity of TCF, indicate that other substances aside from organohalogens contribute to the high methanogenic toxicity in bleaching effluents. Literature data is presented suggesting that wood resin compounds released by alkaline extraction stages might be important inhibitory substances in all bleaching processes. Oxygen-delignified bleaching effluents of eucalyptus were found to be highly biodegradable. When tested at subtoxic concentrations, the chlorine and TCF bleaching effluent COD were anaerobically degraded by 67 and 75%, respectively. In both cases, methane production accounted for most of the COD removed. Therefore, the TCF process also enhances the anaerobic biodegradability of bleaching effluents to a small extent.

Two mannanases from Sclerotium rolfsii in total chlorine free bleaching of softwood kraft pulp

The plant pathogenic basidiomycete Sclerotium rolfsii produces a wide range of extracellular hemicellulolytic enzymes. To study the effect of β-mannanases in total chlorine free bleaching of softwood pulp, two purified β -mannanases from S. rolfsii, with molecular masses of 42 and 61 kDa, a xylanase preparation from S. rolfsii and combinations of these were tested in a O(QX)P bleaching sequence (O = oxygen delignification, X = treatment with enzymes, Q = chelation of metals, P = treatment with hydrogen peroxide in alkaline solution). A brightness increase of 1.6 and 1.9% ISO was obtained with the 42 and 61 kDa mannanase and a combination of each of these enzymes with xylanases gave a brightness increase of 2.5 and 2.8% ISO, respectively. The effect of mannanases and xylanases was nearly additive. Both mannanases alone caused a lower decrease of the kappa number as compared to xylanases. The mannanases differed in their ability to release oligosaccharides from different mannans. The 61 kDa mannanase liberated larger fragments and caused rapid depolymerisation of mannans, which seems to promote the bleaching of pulp.

Metal Ion Content of Material Removed from the Surface of Unbleached Kraft Fibres

Distribution and attachment of metal ions to the pulp components in kraft pulps can affect the possibilities to achieve a metal ion profile favourable for total chlorine free bleaching. By enrichment and analysis of different morphological fractions of the pulp, such as material from the fibre surface and ray cells, the metal ion distribution (Fe, Cu, Mn. Mg and Ca) in a commercial unbleached softwood kraft pulp (kappa number 32) was investigated. Material removed from the surface of unbleached kraft fibres and the fraction containing the ray cells were found to have a considerably higher metal ion content than the rest of the pulp. There was good correlation between the content of manganese and calcium and the content of lignin and carboxy groups. Distribution patterns of metal ions in the pulp appear to resemble those found in the wood. The metal profile in the pulp was studied also following EDTA treatment. Metal ions remaining in the pulp after the EDTA treatment were still unevenly distributed, with high levels in the surface material and the ray cell enriched fraction