NITRIFICATION, DENITRIFICATION, AND DECHLORINATION IN BLEACHED KRAFT PULP-MILL WASTE-WATER

This study deals with combining the biological removal of organic halo gens with the removal of nitrogen from bleached kraft pulp mill wastew ater in fluidized-bed reactors under nitrifying and denitrifying condi tions, Untreated and biotreated bleached kraft pulp mill wastewaters h ad no detrimental effect on nitrification or denitrification. The nitr ifying biofilm reactor, pregrown on synthetic inorganic feed with ammo nia, removed without a lag phase adsorbable organic halogens [7.2 mg C l (g biomass volatile solids)(-1)day(-1)] from bleached kraft pulp mil l wastewater and selected chlorophenols from synthetic wastewater. Ele ctron microscopical examination of the biofilm showed that bacteria, m orphologically similar to the nitrifying species Nitrosomonas or Nitro bacter, and Nitrosospira were dominant. The denitrifying fluidized-bed reactor, pregrown on nitrate and methanol, denitrified without a lag phase bleached kraft pulp mill wastewater. Under denitrifying conditio ns, 35% of the total organic carbon content of untreated bleached kraf t pulp mill wastewater was removed. The reducing power delivered by un treated bleached kraft pulp mill wastewater for denitrification was 2 mmol electrons/mmol carbon mineralized. Dechlorination under denitrify ing conditions was negligible.