THE USE OF MICROORGANISMS FOR THE REMOVAL OF SULFATES ON ARTISTIC STONEWORKS

One of the most important causes of decay of calcareous stones is due to the conversion of calcium carbonate into calcium sulphate (gypsum). In order to optimise a strategy for the removal of the sulphates from artistic stoneworks, a procedure based on the use of sulphate-reducin g bacteria, has been established. Different strains of Desulfovibrio i n pure and mixed cultures were tested in batch to verify their sulphat e-reducing potentiality. The biomasses of the selected strains, D. des ulfuricans 1 and D. vulgaris, were applied under anaerobic conditions to the sample surfaces directly and after adhesion to sepiolite used a s a substratum. Stone samples artificially enriched with sulphates and real fragments of a marble column and a marble statue were treated. T he results obtained show that sulphate removal was more effective on r eal samples than on artificially enriched samples and in the both case s when the treatment was performed using sepiolite as substratum. The best result was obtained on the statue fragment with 81% sulphate remo val after 36 h (against 20% for control). (C) 1997 Elsevier Science Lt d.