ASSESSMENT OF DESIGN AND OPERATING PARAMETERS FOR HIGH-RATE ANAEROBIC DECHLORINATION OF SEGREGATED KRAFT MILL BLEACH PLANT EFFLUENTS

The removal of organochlorine from segregated kraft mill bleach plant wastewaters using high rate anaerobic reactors was investigated at bench scale. Modified sludge blanket reactors with long solids retention times were utilized in the study and the adsorbable organic halogen (AOX) technique was used as a measure of wastewater organo-chlorine content. The factors investigated for influence on dechlorination included the presence or absence of synthetic evaporator condensate as a cosubstrate, hydraulic retention time, and wastewater dilution. Removal efficiencies of AOX ranging from 27 to 65% were observed over hydraulic retention times ranging from 3 to 48 hours. Although bleach plant wastewaters have been reported to be extremely inhibitory to methanogens, methane production was observed under all conditions imposed on the biomass in this study. Approximately 3% of the influent AOX remained in the treated effluent as nonfilterable AOX. Accumulation of AOX in the reactor contents was found to account for 5% of the cumulatives influent AOX.