CHEMICAL-REDUCTION OF AOX AND COD FROM HARDWOOD KRAFT CHLORINATION-STAGE EFFLUENT

This article examines the use of alkali [NaOH or Ca(OH)2] and alum [Al 2(SO4)3] to reduce AOX (adsorbable organic halogen) and COD (chemical oxygen demand) in chlorine-stage (C-stage) effluent for hardwood kraft pulps. Tests were conducted on the whole effluent and on its molecula r-weight fractions. The results indicate that 80% of the AOX in the C- stage effluent can he removed by treating the effluent with NaOH at pH 12.5 prior to conventional sedimentation with alum. Ether extraction of the hardwood C-stage effluent before and after chemical treatment s uggests that these extractives are the primary source of residual AOX.