Anaerobic treatment of natural tannin extracts in UASB reactors
López-Fluza, J.; Omil, F.; Méndez, R.
Water Science and Technology a Journal of the International Association on Water Pollution Research 48(6): 157-163
2003
ISSN/ISBN: 0273-1223 PMID: 14640213 Document Number: 564448
Tannin extracts are substances commonly used in leather production processes. Since most of the steps of tannery manufacturing processes are carried out in aqueous environments, the presence of these compounds in waste waters is important. The aim of this work is to study the feasibility of the anaerobic degradation of three natural tannin extracts in three Upflow Anaerobic Sludge Blanket reactors, which were fed with increasing concentrations of two condensed (quebracho and wattle) and one hydrolysable tannin extract (chestnut). Concentrations of applied extracts were 100, 200, 400, 800 and 1000 mg/litre, and 5 g/litre of glucose was used as cosubstrate. Reactors were operated during 210 days and their performance was evaluated from the values of total and soluble chemical oxygen demand (COD), total and intermediate alkalinity, volatile fatty acids, pH and UV absorption at 280 nm. COD removal efficiencies higher than 85% were achieved in all cases. However, tannin extract removal efficiencies (based on UV-280 nm absorption measurements) were significantly lower, ~20% for condensed extracts and 60% for the hydrolysable one, when the reactors operated with the highest tannin extract concentration. The operation of the reactors was stable, commonly with alkalinity ratios below 0.30. Mass balances carried out indicate that most of the COD removal efficiencies are due to the removal of the readily biodegradable organic matter (glucose), whereas the tannin extracts are hardly anaerobically biodegradable, especially condensed extracts (wattle and quebracho).