engleski

Pollution of Croatian Mediterranean soil with sulfur from high-S coal: soil and coal sulfur speciation (XANES) and soil bioremediation (bacterial biomass)

Previously conducted study [1] showed that Plomin soil (eastern part of the Istrian Peninsula, North Adriatic, Croatia) is highly sulfurous (up to 4% total S) due to historic combustion of superhigh- organic-sulfur (SHOS) Raša coal (up to 11% S). It was used in a local coal-fired power plant during the period 1970-2000. Moreover, the local environment is polluted with selenium [2, 3], which is also incresed in SHOS coal. Due to high levels of soil pollution with SHOS coal particles, it is necessary to apply some clean-up measures to improve the environmental quality as sulfur is known for its harmful effects on the environment. Among them, bioremediation is deemed as promising method since it is cost effective and eco- friendly. Biological processes have no harmful products compared to chemical ones. They can remove both organic and inorganic compounds from soil or coal without alteration of their value [4]. Although the removal of organic S using bacteria is a complex process, it has been shown [5] that some types of bacteria can successfully decrease concentration of total S. Due to very high organic S levels in Raša coal, their characterization was conducted by many studies in the past using different destructive and nondestructive methods. Among nondestructive techniques, several research groups used sulphur K-edge and L-edge X ray absorption spectroscopy (XANES) to determine organic and inorganic S constituents in Raša coal. Reports have showed that the organic S content was 70% thiophenic. Controversy regarding the origin of the organic S part exists with discussions whether it belongs to aryl sulphide or alkyl sulphide. The aim of this study is to determine the speciation of S in SHOS coal and soil, and to test a bioremediation efficiency in terms of bacterial desulfurization of soil. The study area is a karst terrain composed of carbonate rocks, overlain by reddish terra rossa soil. Soil samples were air dried and sieved through a 2-mm sieve. Several topsoil and coal samples were analyzed by XANES technique. Mortar with pestle were used to crush and mix samples to achieve better homogeneity. 100 mg of each sample was pressed in standard press obtaining pellets of 1 cm in diameter. Energy calibration was performed on elemental S in transmission mode. All samples were measured in vacuum and in fluorescence mode by collecting three spectra per sample to ensure the reproducibility of the data. For the purpose of bioremediation, soil and coal powder samples were analyzed for their trace element levels using atomic absorption spectroscopy (AAS), while total S was examined with CNHS analyzer. Thereafter, 1 gram of sample powder was added to 10 ml of double distilled water and filtered. The solution was inoculated on petri plates containing solid media (peptone 0.5 %, yeast extract 0.5 %, glucose 1 % and agar 3 %). Following 24-hour period, the developed bacterial colonies were picked up and transferred into liquid media (peptone 0.5 %, yeast extract 0.5 % and glucose 1 %) for their identification and mass cultivation. Bacterial consortium consisting of exponential phase cells has been provided through centrifugation and repeated washing. Bacterial pellets were mixed in solution of sodium alginate prepared in basal media. The mixture was pumped dropwise into CaCl2 solution in order to get beads under sterilized conditions in a laminar flow cabinet. Beads were resuspended in the basal media and used for the removal of sulfur. Solution of sample powder was treated with bacterial beads where one bead equals to 10 mg of dry weight of bacteria. Following the treatment, concentrations of total S and trace metals are measured again to determine bacterial clean-up efficiency. The results will provide basic information on organic and inorganic pollution control and environmental management in the Croatian coastal locality.

sulfur ; soil ; coal ; bioremediation

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