Xylanase and laccase based enzymatic kraft pulp bleaching reduces adsorbable organic halogen (AOX) in bleach effluents: A pilot scale study

• Cost-effective production of xylanase and laccase up to 10 kg substrate.
• Sequential enzymatic treatment of pulp proved better than individual treatments.
• Enzymatic pre-treatment of pulp reduced 35% ClO2 in ECF bleaching.
• Enzyme treatment at pilot scale lowered AOX levels by 34% in effluents.
• Enzyme treatment at pilot scale led to reduction in PC No. of pulp by 50%.

In present study, xylanase and laccase were produced in a cost-effective manner up to 10 kg substrate level and evaluated in elemental chlorine free bleaching of Eucalyptus kraft pulp. Compared to the pulp pre-bleached with xylanase (15%) or laccase (25%) individually, the ClO2 savings were higher with sequential treatment of xylanase followed by laccase (35%) at laboratory scale. The sequential enzyme treatment when applied at pilot scale (50 kg pulp), resulted in improved pulp properties (50% reduced post color number, 15.71% increased tear index) and reduced AOX levels (34%) in bleach effluents. The decreased AOX level in effluents will help to meet AOX discharge limits, while improved pulp properties will be value addition to the paper.