Reduction of AOX by Prolonged ClO2 Bleaching under High Temperature and Acidic pH Conditions

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Decreases in AOX during chlorine dioxide bleaching at high temperatures and under acidic conditions were investigated. When the temperature in the chlorine dioxide bleaching stage was raised from 70°C to 95°C, a certain decrease in AOX was detected. AOX is formed by a chlorine substitution reaction with mainly lignin and chlorine that was generated from a reduction of chlorine dioxide. For the chlorination of lignin, it appears that raising the temperature facilitated an oxidation reaction rather than a substitution reaction, so that the rapid consumption of chlorine in the oxidation reaction suppressed the substitution reaction.<BR>Extension of the bleaching period from 15 min to 90 min also decreased AOX discharge. In the first chlorine dioxide stage in bleaching, high temperature and acidic pH were employed to hydrolyze hexeneuronic acid as well as remove lignin. In this bleaching condition, some of the lignin was also subjected to hydrolysis. However, the cause of a dehalogenation reaction that was required to decrease AOX is difficult to understand. To determine the cause of dehalogenation, some chlorinated compounds such as a chlorinated aromatic compound and a chlorinated organic acid were heated at 95°C for 90-120 min under acidic conditions. However, no explanation could be found to account for the decrease in AOX. Therefore, further investigation should be conducted to determine why the AOX reduction was induced by prolonging the bleaching period.
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杉元倫子
(独)国際農林水産業研究センター林業領域

Reduction of AOX by Prolonged ClO2 Bleaching under High Temperature and Acidic pH Conditions

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