Effect of Electron Acceptor on Hydrocarbon Pollution Degradation Rate Caused by Bacteria of the Genus Rhodococcus under Anaerobic Conditions

Abstract

The effect of the concentration of an oxygen acceptor in the form of a nitrate-containing salt on the rate and mechanism of hydrocarbon degradation (HC) in actual soil samples extracted from wells of 1 to 5 m in depth from areas allocated for future urban development under the influence of bacterial strains belonging to the genus Rhodococcus (R. ruber Ac-1513 D and R. erythropolis Ac-1514 D) is studied. Initial soil samples containing up to 9.8% HC were capable of producing biogas for 59 years under anaerobic conditions, in the absence of an oxygen acceptor, under the influence of methane-forming indigenous microorganisms. At the same time, the content of fire-dangerous methane in gas products ranged from 8 to 36%, which makes housing development in such areas unacceptable without preliminary treatment. To accelerate hydrocarbon degradation by oil-oxidizing bacteria under non-specific oxygen-free conditions, it was proposed to use an electron acceptor, calcium nitrate. The mechanism of hydrocarbon degradation in the presence of Ca(NO3)2 through denitrification has been established. It is shown that effect of calcium nitrate studied in the presence of three concentrations (1.25, 2.5, and 5.0%) on denitrification and anaerobic HC degradation was reversely proportional, which may be associated with the inhibition of the denitrification process by high concentrations of Ca(NO3)2. In the presence of a minimum concentration of calcium nitrate (1.25%), maximum rates of anaerobic HC degradation in the soil are of k = 1.27 and 0.32 year–1 during warm and cold seasons, respectively. The content of the main non-flammable reaction product, carbon dioxide in the gas mixture was 99% by volume. Thus, the complete decomposition of the hydrocarbon and the gas generation phase may be completed within 1 year, which is 59 times faster than processes occurring in the absence of an oxygen acceptor.