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| The short- and long-term biodegradation behaviours of wattle, bayberry, valonia and chestnut tannin extracts, widely employed as vegetable tanning agents in leather industry, were studied in this paper. The results indicated that the four tannin extracts are biodegradable and should not show toxic effects on the respiration of activated sludge organisms. It is proved that the short-term biodegradabilities of the four tannin extracts are concentration dependent. Low concentration of the tannin extracts could be effectively biodegraded, but the biodegradation processes should be retarded when they present in wastewater at high concentrations, owing to the inhibitory effects of tannins on activated sludge process. In general, the short-term biodegradability of the four tannin extracts follows the sequence: valonia>chestnut>bayberry>wattle. The long-term biodegradation behaviours of the four tannin extracts showed that they could be thoroughly biodegraded with the prolongation of activated sludge process, even if they present in wastewater at high concentrations. It is therefore suggested that both the condensed tannin extracts (wattle and bayberry extracts) and the hydrolysable ones (valonia and chestnut extracts) are environmentally friendly leather chemicals, in consideration of their biodegradabilities. |
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| Keywords:leather making;vegetable tannin extract;biodegradability;BOD |
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