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 aerobic, one single anaerobic and two combined anaerobic-aerobic reactors-were used to treat sulphite pulp chlorine bleaching wastewater. By total mass balances it was proven that the individual compounds followed were removed almost exclusively by biological degradation. The contribution of removal by adsorption on biomass was less than 1% for all the individual chlorophenolic compounds. In the three systems involving an aerobic step, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol were usually quantitatively removed. This was observed up to loadings of 1 mmol 2,4,6-trichlorophenol per m(3) and day. At lower loading rates, trichloroguaiacols were also removed quantitatively. However, 4,5-dichloroguaiacol was only partly removed, whereas 3,5-dichlorosyringol was produced in the reactors from unidentified precursors. The anaerobic-aerobic recycle reactor did remove individual chlorinated phenolics at high loading rates better than the other reactor combinations. In the aerobic systems removal rates of organic chlorine and carbon correlated well with removal rates estimated from individual chlorophenols measurements, despite its low contribution to the total values (<<1%).