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Juha Fiskari--This investigation studied the toxicity of the filtrates in partially closed TCF and ECF bleaching sequences. A series of experiments was performed with oxygen-delignified hardwood (birch) and softwood pulp samples from Finnish pulp mills. The bleaching filtrates were recirculated in order to simulate the liquid circulations of a partially closed bleach plant. The conditions (chemical charges, retention times, temperatures) were similar to those of an actual mill. The filtrates were then analyzed for toxicity with a rapid Photobacterium test developed by the Finnish Pulp and Paper Research Institute (KCL). According to the results, the toxicity of the first chlorine dioxide stage (D0) filtrates was significantly higher than that of ozone or alkaline hydrogen peroxide stage filtrates. The TCF bleaching filtrates showed little or no toxicity. In general, the ECF bleaching filtrates had higher toxicity than the TCF bleaching filtrates. The softwood ECF bleaching filtrates had higher toxicity than the hardwood ECF bleaching filtrates.
Product code: ENV01119Author: Fiskari, J.
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