Destruction of toluene and xylene by sulfatе-reducing bacteria

As a result of human activity aromatic hydrocarbons enter the environment in large quantities, contaminating it. Dropping of insufficiently treated wastewater drains considerably decrease the quality of water. Quite effective biological methods of purification of contaminated environment are the usage of microorganisms. Prospective microorganisms for sewage treatment are sulfate-reducing bacteria. The purpose of the work was to investigate the ability of sulfate-reducing bacteria to use xylene and toluene as a source of carbon under different cultivation conditions.  The study objects were sulfate-reducing bacteria Desulfotomaculum AR1 and Desulfovibrio desulfuricans Ya-11. The biomass of bacteria was determined turbidimetrically, the content of sulfate ion and hydrogen sulfide – photometrically in the culture fluid. The content of fumarate was determined by the method of high-performance liquid chromatography. The ability of Desulfotomaculum AR1 and D. desulfuricans Ya-11 bacteria to use toluene and xylene as the sole source of carbon and energy has been established. In the toluene environment, a better growth of bacteria was observed. A comparison was made between the efficiency of the reduction of sulfate ions and the growth of bacteria in the control medium and the medium with aromatic compounds. The efficiency of sulfate ions reduction was sufficiently high in the control medium, whereas in the toluene/xylene media the efficiency of sulfate utilization and hydrogen sulfide accumulation was lower compared to the control parameters. The growth of Desulfotomaculum AR1 and D. desulfuricans Ya-11 sulfate-reducing bacteria was investigated in xylene and toluene media in the presence/absence of fumarate. According to the results of the studies, the best growth of the tested bacteria was observed in the medium with aromatic compounds in the presence of fumarate and sulfate ion. Efficiency of use of fumarate in the medium with toluene with bacteria Desulfotomaculum AR1 was more than 90 %. Fumarate can be used by sulfate-reducing bacteria as a source of carbon, donor and acceptor of electrons. Fumarate is most likely to inhibit sulfate reduction in Desulfotomaculum AR1 and D. desulfuricans Ya-11 bacteria, as indicated by studies showing that sulfate reduction efficiency in lactate, fumarate, and sulfate ion media was half that of control. Sulfate-reducing bacteria are capable to anaerobically degrade aromatic hydrocarbons in the presence of sulfate ions as terminal electron acceptors. The ability of sulfate-reducing bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 to use the aromatics of the BTEХ – toluene, xylene and sulfate-ions, makes them promising at the biological purification step of contaminated wastewater from these pollutants.