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| The biodegradabilities of three kinds of typical organic tanning and/or retanning agents, namely aromatic syntans, aldehyde tanning agents and acrylic syntans, were studied in this paper. The results showed that the biodegradation behaviours of the leather chemicals are closely associated with their molecular weight and structure together with their chemical composition. It is suggested that the employment of organic tanning and/or retanning agents in leather industry might result in different environmental impacts even for the same kind of syntans. The tested four aromatic syntans (SGP, PGP, KWOP and BS) exhibited different but generally low biodegradability. The phenol syntan SGP could not be biodegraded, and the phenol-sulphone syntan PGP exhibited strong inhibitory effects on activated sludge respiration. Comparatively, the naphthalene syntan BS and the phenol syntan KWOP showed somewhat better biodegradability. In the case of aldehyde tanning agents, both formaldehyde and glutaraldehyde are toxic to activated sludge organisms, and comparatively the latter is potential to cause more severe environmental problem when it was used in leather industry. However, an aliphatic aldehyde product, namely syntan SH, did not show toxicity to activated sludge and it was biodegradable when it was at the concentrations tested. As far as acrylic syntans were concerned, the results indicated that the commercial anionic products (R83, B7815, ART-I and ART-II) were not so much inhibitory but were hardly biodegraded. However, a cationic product ART-III is potential to inhibit the activated sludge process in the effluent treating yard of tannery when it presented at high content. |
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| Keywords:tanning agent;activated sludge;biodegradability;BOD |
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