ANAEROBIC-AEROBIC FLUIDIZED-BED BIOTREATMENT OF SULFITE PULP BLEACHING EFFLUENTS .2. FATE OF INDIVIDUAL CHLOROPHENOLIC COMPOUNDS

Four parallel biological fluidized bed reactor systems-one single aero bic, one single anaerobic and two combined anaerobic-aerobic reactors- were used to treat sulphite pulp chlorine bleaching wastewater. By tot al mass balances it was proven that the individual compounds followed were removed almost exclusively by biological degradation. The contrib ution of removal by adsorption on biomass was less than 1% for all the individual chlorophenolic compounds. In the three systems involving a n aerobic step, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichloro phenol were usually quantitatively removed. This was observed up to lo adings of 1 mmol 2,4,6-trichlorophenol per m(3) and day. At lower load ing rates, trichloroguaiacols were also removed quantitatively. Howeve r, 4,5-dichloroguaiacol was only partly removed, whereas 3,5-dichloros yringol was produced in the reactors from unidentified precursors. The anaerobic-aerobic recycle reactor did remove individual chlorinated p henolics at high loading rates better than the other reactor combinati ons. In the aerobic systems removal rates of organic chlorine and carb on correlated well with removal rates estimated from individual chloro phenols measurements, despite its low contribution to the total values (<<1%).