Treatment and detoxification of aqueous spruce bark extracts by Aspergillus niger

James A Field, G. Lettinga

Research output: Chapter in Book/Report/Conference proceedingConference contribution

38 Citations (Scopus)

Abstract

Debarking effluents of the forest industry are severely toxic waste streams due to their high tannin content. The objectives of this study were to evaluate the treatment and detoxification of debarking wastewater with tannin tolerant fungi. For this purpose, Aspergillus niger was cultivated on aqueous bark extracts and the toxicity was assayed utilizing methanogenic bacteria as the test organism. Sterilized aqueous extracts of spruce bark were diluted to 5.2 g COD L-1 (containing 2.7 g tannin COD L-1) in either citrate or tartrate buffer and inoculated with A. niger spores. During four day aerobic fermentations with citrate buffer, the elimination of unfiltered and soluble COD was 28 and 63%, respectively. The apparent yield of biomass averaged 34% of the extract COD; however, 12% of the extract COD was tannins adsorbed on the fungal biomass. The decrease in the tannin concentration was 50%. According to gel chromatography results, the original oligomeric tannins that resisted biodegradation were those of the highest MW. The toxicity was consequently only partially reduced by the fermentation. During the tartrate buffered fermentations, the pH rose due to the metabolism of the organic acid in the buffer. The rise in pH beyond 6 promoted autoxidative reactions that caused extensive polymerization of the tannins which resisted biodegradation. This resulted not only in an enhanced elimination of the tannins but also in a complete detoxification of the extracts. Similar levels of detoxification could be obtained in sterile un-inoculated extracts by autoxidation alone (raising the pH and aerating the extracts). Likewise, extracts fermented in citrate buffer could be completely detoxified by a subsequent autoxidation treatment. The exclusion peak of the gel chromatograms (MW > 30,000 g mole-1) obtained from the highly autoxidized samples accounted for 53% of the UV absorbance, whereas no exclusion peak was present in the unoxidized extracts. For the biological treatment and detoxification of debarking wastewaters, we recommend the cultivation of tannin tolerant fungi followed by short autoxidation treatments that polymerize the oligomeric tannin fraction resisting biodegradation to non-toxic high molecular weight polymers.

Original languageEnglish (US)
Title of host publicationWater Science and Technology
Pages127-137
Number of pages11
Volume24
Edition3-4
StatePublished - 1991
Externally publishedYes
EventProceedings of the 3rd IAWPRC Symposium on Forest Industry Wastewaters - Tampere, Finl
Duration: Jun 5 1990Jun 8 1990

Other

OtherProceedings of the 3rd IAWPRC Symposium on Forest Industry Wastewaters
CityTampere, Finl
Period6/5/906/8/90

Fingerprint

tannin
detoxification
bark
fermentation
biodegradation
gel
fungus
toxicity
methanogenic bacterium
wastewater
biomass
absorbance
organic acid
polymerization
chromatography
spore
polymer
metabolism
effluent

ASJC Scopus subject areas

  • Water Science and Technology

Cite this

Field, J. A., & Lettinga, G. (1991). Treatment and detoxification of aqueous spruce bark extracts by Aspergillus niger. In Water Science and Technology (3-4 ed., Vol. 24, pp. 127-137)

Treatment and detoxification of aqueous spruce bark extracts by Aspergillus niger. / Field, James A; Lettinga, G.

Water Science and Technology. Vol. 24 3-4. ed. 1991. p. 127-137.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Field, JA & Lettinga, G 1991, Treatment and detoxification of aqueous spruce bark extracts by Aspergillus niger. in Water Science and Technology. 3-4 edn, vol. 24, pp. 127-137, Proceedings of the 3rd IAWPRC Symposium on Forest Industry Wastewaters, Tampere, Finl, 6/5/90.
Field JA, Lettinga G. Treatment and detoxification of aqueous spruce bark extracts by Aspergillus niger. In Water Science and Technology. 3-4 ed. Vol. 24. 1991. p. 127-137
Field, James A ; Lettinga, G. / Treatment and detoxification of aqueous spruce bark extracts by Aspergillus niger. Water Science and Technology. Vol. 24 3-4. ed. 1991. pp. 127-137
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abstract = "Debarking effluents of the forest industry are severely toxic waste streams due to their high tannin content. The objectives of this study were to evaluate the treatment and detoxification of debarking wastewater with tannin tolerant fungi. For this purpose, Aspergillus niger was cultivated on aqueous bark extracts and the toxicity was assayed utilizing methanogenic bacteria as the test organism. Sterilized aqueous extracts of spruce bark were diluted to 5.2 g COD L-1 (containing 2.7 g tannin COD L-1) in either citrate or tartrate buffer and inoculated with A. niger spores. During four day aerobic fermentations with citrate buffer, the elimination of unfiltered and soluble COD was 28 and 63{\%}, respectively. The apparent yield of biomass averaged 34{\%} of the extract COD; however, 12{\%} of the extract COD was tannins adsorbed on the fungal biomass. The decrease in the tannin concentration was 50{\%}. According to gel chromatography results, the original oligomeric tannins that resisted biodegradation were those of the highest MW. The toxicity was consequently only partially reduced by the fermentation. During the tartrate buffered fermentations, the pH rose due to the metabolism of the organic acid in the buffer. The rise in pH beyond 6 promoted autoxidative reactions that caused extensive polymerization of the tannins which resisted biodegradation. This resulted not only in an enhanced elimination of the tannins but also in a complete detoxification of the extracts. Similar levels of detoxification could be obtained in sterile un-inoculated extracts by autoxidation alone (raising the pH and aerating the extracts). Likewise, extracts fermented in citrate buffer could be completely detoxified by a subsequent autoxidation treatment. The exclusion peak of the gel chromatograms (MW > 30,000 g mole-1) obtained from the highly autoxidized samples accounted for 53{\%} of the UV absorbance, whereas no exclusion peak was present in the unoxidized extracts. For the biological treatment and detoxification of debarking wastewaters, we recommend the cultivation of tannin tolerant fungi followed by short autoxidation treatments that polymerize the oligomeric tannin fraction resisting biodegradation to non-toxic high molecular weight polymers.",
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AB - Debarking effluents of the forest industry are severely toxic waste streams due to their high tannin content. The objectives of this study were to evaluate the treatment and detoxification of debarking wastewater with tannin tolerant fungi. For this purpose, Aspergillus niger was cultivated on aqueous bark extracts and the toxicity was assayed utilizing methanogenic bacteria as the test organism. Sterilized aqueous extracts of spruce bark were diluted to 5.2 g COD L-1 (containing 2.7 g tannin COD L-1) in either citrate or tartrate buffer and inoculated with A. niger spores. During four day aerobic fermentations with citrate buffer, the elimination of unfiltered and soluble COD was 28 and 63%, respectively. The apparent yield of biomass averaged 34% of the extract COD; however, 12% of the extract COD was tannins adsorbed on the fungal biomass. The decrease in the tannin concentration was 50%. According to gel chromatography results, the original oligomeric tannins that resisted biodegradation were those of the highest MW. The toxicity was consequently only partially reduced by the fermentation. During the tartrate buffered fermentations, the pH rose due to the metabolism of the organic acid in the buffer. The rise in pH beyond 6 promoted autoxidative reactions that caused extensive polymerization of the tannins which resisted biodegradation. This resulted not only in an enhanced elimination of the tannins but also in a complete detoxification of the extracts. Similar levels of detoxification could be obtained in sterile un-inoculated extracts by autoxidation alone (raising the pH and aerating the extracts). Likewise, extracts fermented in citrate buffer could be completely detoxified by a subsequent autoxidation treatment. The exclusion peak of the gel chromatograms (MW > 30,000 g mole-1) obtained from the highly autoxidized samples accounted for 53% of the UV absorbance, whereas no exclusion peak was present in the unoxidized extracts. For the biological treatment and detoxification of debarking wastewaters, we recommend the cultivation of tannin tolerant fungi followed by short autoxidation treatments that polymerize the oligomeric tannin fraction resisting biodegradation to non-toxic high molecular weight polymers.

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