Thermophilic anaerobic-aerobic treatment of bleach kraft mill effluent (BKME) at 55°C was studied using reactors partially packed with polyurethane carrier material. The wastewater was a mixture of chlorination stage and alkaline extraction stage effluents from softwood pulping. Both the thermophilic anaerobic and aerobic treatments provided about 40-45% COD and AOX removals at loading rates of about 13-2.5 kg COD m−3 d−1, which corresponded with hydraulic retention times of 17.6-30 h. The aerobic post-treatment removed less than 10% of the COD and AOX present in the anaerobically treated BKME.

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