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Chemical and biological characteristics of chlorinated organic compounds in spent kraft bleaching liquors



Chemical and biological characteristics of chlorinated organic compounds in spent kraft bleaching liquors



Bulletin for the Forestry & Forest Products Research Institute (340): 1-106



To investigate the chemical constituents of kraft bleach effluents prepared in the laboratory from beech wood, the organic compounds in the effluents were separated into high (H) and low (L) molecular weight fractions by means of ultrafiltration, adsorbed chromatography, and liquid-liquid extraction. To clarify the effects of the chlorination condition on the formation of chlorinated organic compounds in bleaching spent liquors, beech, red-pine kraft pulps and some model compounds were chlorinated under various conditions such as Cl2-dosage, pH, temperature and lignin content. It was found that Cl2-dosage and lignin contents in pulps have a potent influence on the formation of total organic chlorine (TOCl) and chlorinated phenols (PhCl) during chlorination. The toxicity of the organic matter fractionated from beech kraft-bleach effluents was bioassayed by using an activated sludge. The toxicants were included in the spent liquors of the chlorination (C) and caustic-extraction (E) stages, whereas the liquor from the chlorine-dioxide stage was almost free of toxicants. The ethyl-ether soluble fraction, which accounted for a substantial portion of the toxicity of the kraft-bleach effluents, was more toxic in the acidic region of pH 4-6 than in the region of pH 7-9. The chlorinated low molecular-weight compounds present in the liquor were primarily responsible for the toxicity acting against the activated sludge and were well absorbed by macroleticular resin (Amberite XAD-4). The results showed that the toxicity intensity was stronger in the acid region of pH and that the organically-bound chlorine and phenolic-hydroxyl group of these compounds seemed to play an important role in their toxicity. The high molecular-weight fraction in the spent liquors showed no toxicity, but became toxic when it was decomposed to low molecular-weight compounds by alkaline cupric-oxide oxidation. In the chlorinated model-compounds, containing methoxyl groups, the cleavage of the C-Cl bonds in the presence of nitrogen promoted demethoxylation reaction. Chlorinated compounds like PCOL were decolorized easily, and they decomposed because of the high inductivity of the C-Cl bonds in comparison with the nonchlorinated bonds upon being subjected to oxidative UV-light irradiation.

Accession: 004935660

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