The use of microorganisms for the removal of sulphates 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-reducing bacteria, has been established. Different strains of Desulfovibrio in pure and mixed cultures were tested in batch to verify their sulphate-reducing potentiality. The biomasses of the selected strains, D. desulfuricans 1 and D. vulgaris, were applied under anaerobic conditions to the sample surfaces directly and after adhesion to sepiolite used as a substratum. Stone samples artificially enriched with sulphates and real fragments of a marble column and a marble statue were treated. The results obtained show that sulphate removal was more effective on real samples than on artificially enriched samples and in the both cases when the treatment was performed using sepiolite as substratum. The best result was obtained on the statue fragment with 81% sulphate removal after 36 h (against 20% for control). (C) 1997 Elsevier Science Ltd.