DISSOLUTION OF BARIUM FROM BARITE IN SEWAGE SLUDGES AND CULTURES OF DESULFOVIBRIO-DESULFURICANS

High concentrations of total barium, ranging from 0.42 to 1.58 mg . g( -1) (dry weight) were found in sludges of two sewage treatment plants near Florence, Italy, Barium concentrations in the suspended matter de creased as redox potential values changed from negative to positive, A n anoxic sewage sludge sample was aerated, and 30% of the total barium was removed in 24 h, To demonstrate that barium was solubilized from barite by sulfate-reducing bacteria, a strain of Desulfovibrio desulfu ricans was used to study the solubilization of barium from barite unde r laboratory conditions, During cell growth with different concentrati ons of barite from 0.01 to 0.3 g . liter(-1) (the latter is the MIC) a s the only source of sulfates in the cultures, the D. desulfuricans st rain accumulated barium up to 0.58 mu g . mg(-1) (dry weight), Three t imes the quantity of barium was dissolved by bacteria than in the unin oculated medium (control), The unexpectedly low concentration of solub le barium (1.2 mg of Ba . liter(-1)) with respect to the quantity expe cted (109 mg of Ba . liter(-1)), calculated on the basis of the free H 2S evolved from the dissimilatory reduction of sulfate from barite, wa s probably due to the formation of other barium compounds, such as wit herite (BaCO3) and the transient species barium sulfide (BaS), The D, desulfuricans strain, growing on barite, formed visible aggregates, Co nfocal microscopy analysis showed that aggregates consisted of bacteri a and barite, After 3 days of incubation, several autofluorescent crys tals surrounded by a dissolution halo were observed, The crystals were identified as BaS by comparison with the commercial compound.