Oxidative detoxification of aqueous bark extracts. Part I: Autoxidation

Abstract

The aqueous extracts of bark were studied as a model for wet debarking wastewater. These extracts are known to contain a high concentration of methanogenic toxic tannins. The objective of this study was to modify the native bark tannins (oligomers) with oxidative methods in order to decrease their methanogenic toxicity. The tannins were polymerized by autoxidation, forming colored high-molecular-weight tannins that were non-toxic to methanogenic bacteria. The autoxidation of pine bark extracts provided complete detoxification. In the case of spruce bark, which was responsible for extracts of higher toxicity, the detoxification was either partial or complete depending on the specific sample of spruce bark porn which the extract was prepared. The autoxidation of birch bark did not result in significant detoxification. Although the oligomeric tannins were effectively polymerized, birch bark extracts contain non-tannin toxins which were not affected by the autoxidation and evidence that highly toxic intermediates were formed during the high pH autoxidation of birch bark extracts is presented.Autoxidative detoxification offers an interesting approach for pretreating coniferous bark wastewaters. The oxidation reactions of the pretreatment serve to detoxify the largely non-BOD tannin paction. Thus the methanogenic * Present address: Department of Chemical Engineering, Universidad Autonoma de Barcelona, 08193Bellaterra (Barcelona), Spain. 15 J . Chem. Tech. Biotechnol. 0268-2575/90/$03.50 0 1990 Society of Chemical Industry. Printed in Great Britain J . A. Field, G . Lettinga, L. H . A . Hahets bacteria are not inhibited during the anaerobic wastewater treatment for removing BOD.

Continuous treatment of the insensitive munitions compound N-methyl-p-nitro aniline (MNA) in an upflow anaerobic sludge blanket (UASB) bioreactor

“…The results obtained in this study confirmed that extended aeration of the anaerobically treated effluent promotes the oxidative transformation of MNA derivatives, particularly under mild alkaline conditions, suggesting the possibility of utilizing such process for effluent treatment. Alkali-catalyzed autoxidation has been shown previously to be an effective method to detoxify tannins, a major class of polyphenolic compounds, by promoting formation of high molecular weight polymers with reduced ability to interact with biological targets due to steric hindrance (Field et al, 1989; Field et al, 1990). Similarly to aromatic amines such as MPD, polyphenolic compounds undergo rapid autoxidation reactions that cause extensive polymerization.…”

Utilization of vegetable tannins for stabilization of collagen fibers by using supported process enzyme

“…Due to increasingly strict regulations on effluent discharge both in Sudan and globally [3], it has become necessary to find ways to fully utilize vegetable tannins and reduce the environmental impact of the tanning process. Several methods have been proposed to achieve this goal, such as pickle less vegetable tanning [12], oxidative degradation of tannin liquors using hydrogen peroxide [13][14], precipitation using zinc sulfate [15], and oxidative detoxification of bark extracts [16]. These methods aim to reduce the pollution load in effluents and promote a more sustainable tanning industry.…”