Impact of Increased Chlorine Dioxide Substitution of the Biotreatability of Chlorinated Organic Compounds, 1993 Environmental Conference Proceedings

The substitution of ClO2 for Cl2 in the first bleaching stage for bleached kraft production has, in many cases, been shown to result in a reduction in the formation of chlorinated organics. However, it is also known that biological wastewater treatment systems remove a significant portion of chlorinated organic compounds entering the treatment facility. This suggests a possible overlap among those compounds whose formation is minimized by increased substitution and compounds which were previously removed during wastewater treatment. In addition, bleaching modifications could potentially alter the distribution of chlorinated organic compounds generated which may affect the biotreatability of the waste stream. Thus, it is not clear that reducing the rate of chlorinated organics formation necessarily translates to an equivalent reduction in quantities of chlorinated compounds discharged in the mill’s treated effluent.

The current study was undertaken to examine the potential impact on the biotreatability (i.e., percent removal) of chlorinated organic compounds associated with the implementation of moderate modifications to an existing softwood bleach line. Bench-scale bioreactors were operated, in duplicate, using influents containing bleach plant filtrates collected at the host mill before and after bleach plant modifications were implemented. Similar removal efficiencies were found under the two conditions for both AOX and chlorinated phenolics.