MICROBIAL REMOVAL OF CHLORINATED PHENOLS DURING AEROBIC TREATMENT OF EFFLUENTS FROM RADIATA PINE KRAFT PULPS BLEACHED WITH CHLORINE-BASED CHEMICALS, WITH OR WITHOUT HEMICELLULASES

The removal of chlorophenolic compounds from kraft mill effluents blea ched with chlorine (cBKME) or chlorine plus hemicellulases (bBKME) was studied in reactors of aerobic treatment lagoons. In these laboratory models, a stable microbial population removed biochemical oxygen dema nd at similar rates of the mill lagoon. Complete removal of nine chlor ophenols and chloroguaiacols during microbial treatment of these efflu ents was detected by gas chromatography. Abiotic removal was only obse rved with 2,4-dichlorophenol and 2,4,5-trichlorophenol. There were no significant differences in degradative ability between microorganisms acclimated to grow in reactors fed with cBKME or bBKME. The latter had a lower content of adsorbable organic halogen and chlorophenols than cBKME. Microorganisms acclimated to cBKME or bBKME were only able to g row on phenol or guaiacol as sole carbon source. However, these microo rganisms removed (0.1-0.5 mM) 4-chlorophenol, 2,4-dichlorophenol and 2 ,4-dichlorophenoxyacetate with BKME as primary carbon source. Under th ese conditions, 2,4,6- and 2,4,5-trichlorophenol, 4,5-dichloroguaiacol , 4,5,6-trichloroguaiacol and tetrachloroguaiacol were not removed. Th ese results suggest that the microbial removal of bleaching chlorophen ols and chloroguaiacols during aerobic treatment, probably takes place only because of their very low concentration (1-200 ppb) in BKME.