ANAEROBIC-AEROBIC FLUIDIZED-BED BIOTREATMENT OF SULFITE PULP BLEACHING EFFLUENTS .1. GLOBAL PARAMETERS

Four parallel biological fluidized bed reactor systems-one single aero bic, one single anaerobic and two combined anaerobic-aerobic-have been used to treat sulphite chlorine pulp bleaching wastewater. It has bee n observed that the AOX removal was limited at 30%, independently of t he wastewater dilution, mode of operation and retention time. Only sma ll differences could be observed between the three systems involving a n aerobic stage. The single aerobic reactor also gave rather competiti ve results with those having an additional anaerobic step, whereas the removal in the single anaerobic reactor was less than the three other systems. Only at high loading rates did the anaerobic-aerobic recycle reactor (AAR) perform better than the other systems. Constant NPOC/AO X ratio, before and after treatment, showed that the chlorinated mater ial was degraded to the same extent as the non-chlorinated one. The re moval by adsorption to biomass and biomass support material was less t han 1% for AOX.