Radiolytic Elimination of Organochlorine in Pulp Mill Effluent

Chlorinated organic compounds, formed during the bleaching of Kraft pulp with chlorine and chlorine dioxide bleaching agents, are commonly measured in pulp mill effluent as adsorbable organic halogen (AOX). Existing biological treatment methods can typically remove less than 50% of the AOX, which may not be adequate for compliance with future regulations. As a potential treatment method, the radiolytic elimination of organochlorine in pulp mill effluent was investigated in bench-scale experiments. Biotreated and untreated effluent as well as E-stage and C-stage filtrates from a pulp mill were irradiated in a cobalt-60 γ-cell. For treated, untreated, E-stage, and C-stage effluent more than 95%, 90%, 70%, and 60% AOX removal was obtained for doses up to 60 kGy, respectively. An increase in organochlorine removal was observed at high pH and in the absence of oxygen. In treated effluent, AOX removal increased from less than 70% in the aerated neutral solution to 80% in the basic media (pH = 12) and to 96% in the absence of oxygen for a dose of 10 kGy.