9.
This article reports the potential of denitrifying activated sludge to degrade highly chlorinated dioxins, especially from
a (landfill) leacheate treatment plant in Japan, and the isolation from this denitrifying activated sludge of a microorganism
able to degrade highly chlorinated dioxins. Using a 700-ml bioreactor, denitrifying activated sludge was cultivated under
denitrifying conditions by adding 2.0 ng of a mixture of 4- to 8-chlorinated dioxins from fly ash. The dioxin contents of
the sample, effluent, and medium before and after cultivation were measured by gas chromatography–mass spectrometry (GC–MS).
After 7 days cultivation, about 90% of added dioxins were lost (average percentage of isomer depletion). A dioxin-degrading
microorganism was isolated from the activated sludge. Lignin was added to the medium as a color indicator of aromatic compound
degradation, and the lignin-decolorizing microorganisms in the denitrifying activated sludge were screened. Some strains were
isolated, and one major isolated fungus, strain 622, decolorized lignin effectively. Strain 622 was identified as an
Acremonium sp. from its morphological characteristics. It could decolorize lignin by 24% under paraffin-sealed anaerobic conditions.
After the cultivation of strain 622 with a 2 ng/ml mixture of 4- to 8-chlorinated dioxins for 1 day, 82% (average for individual
isomers) of the added 4- to 8-chlorinated dioxins had been degraded. Added octachlorodibenzo-
p-dioxin (OCDD, 100 ng) was degraded under aerobic conditions after 8 h of incubation. During this process, heptachlorodibenzo-
p-dioxin was produced and appeared to be a degradation product of OCDD. 1- or 2-hydroxydibenzo-
p-dioxin from OCDD was also identified as the degradation product by GC–MS. These results indicated that OCDD was degraded
to the nonchlorinated dibenzo-
p-dioxins through dechlorination by
Acremonium sp. strain 622.
Received: October 12, 2001 / Accepted: March 11, 2002
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