Use of selected autochthonous soil bacteria to enhanced degradation of hydrocarbons in soil.

A mixed population of soil hydrocarbon degrading bacteria was used to accelerate the biodegradation of a petrochemical waste. An aromatic hydrocarbon storage tank bottom was mixed with soil (10% w/w). After a month 43% of the hydrocarbons were degraded in uninoculated and in fertilized soil, while 65% were degraded in inoculated soil. Nutrient supplemented vermiculite seems to be a good possibility to produce effective hydrocarbon degrading inoculants.

Assessment of the toxic potential of hydrocarbon containing sludges.

A short-time period microbial toxicity test-battery was used for the investigation of acute toxicity and genotoxicity of five hydrocarbon containing sludges. Four sludges were obtained from a petrochemical industry and the fifth from a petroleum refinery. Some of the sludges had been stored for long periods. Bioremediation potential assays for soils polluted with each of the sludges were also considered. The sludges did not show acute toxicity in any of the microbial tests performed. However, when the diethylether soluble fractions of these sludges were analyzed some of them showed acute toxicity, for which the clearest results were obtained with the resazurin reduction method. The greatest toxicity detected with the Resazurin based method was found in the diethylether extracts of the freshly collected (not stored) sludges. On the other hand, the diethylether soluble fraction of those sludges that had been stored showed genotoxicity when analyzed with the Salmonella/microsome assay. After the incorporation of the sludges into the soil, increased bacterial counts were noted and substantial hydrocarbon elimination was achieved in 30 days, showing that bioremediation may be a possible technology for cleaning soils polluted with these sludges.

Effect of petrochemical sludge concentrations of changes in mutagenic activity during soil bioremediation process.

The present study was performed to assess the effect of the petrochemical sludge application rate on the mutagenic activity (Ames test) of soil and the persistence of mutagenic activity during laboratory soil bioremediation process. Sludge-soil systems were prepared at four different sludge application rates (1.25, 2.5, 5, and 10% w/w). Unamended soil was used as a control. Immediately following sludge application, in the absence or presence of S9, a linear correlation between sludge application rates and mutagenicity was found but differed significantly (p < 0.05) from the control system only at higher application rates (5 and 10% w/w). The direct mutagenicity of all systems decreases during the bioremediation process, and after a year of treatment only the 10% system induced a mutagenic response that was significantly different from the control system. On the other hand, an initial increase of the indirect mutagenicity was observed at all application rates. The time required for observing this increase was inversely proportional to the initial sludge concentration. After a year of treatment, the indirect mutagenicity of all sludge-amended soils was not significantly different but was significantly different from the unamended soils. The persistence of the direct mutagenic activity of the sludge-amended soils was related to the sludge concentration, whereas the indirect mutagenic persistence was related to the relationship between easily degradable hydrocarbons and polynuclear aromatic hydrocarbons concentration and independent from the initial application rate.

[Storage of hydrocarbon-degrading bacteria]. / Conservación de bacterias degradadoras de hidrocarburos.

The storage in the laboratory of hydrocarbon degrading bacteria to be used in the decontamination of polluted sites or in the enhancement of biological treatment of industrial effluents was studied. Storage was carried out at 4 degrees C in nutrient agar and in a medium with selection pressure, liquid mineral medium with hydrocarbons. Storage at 4 degrees C with selection pressure and storage at -20 degrees C of 7 gram negative bacilli were compared. The former was the easiest method for preserving the greatest number of strains viable and active.

Conservación de bacterias degradadoras de hidrocarburos / [Storage of hydrocarbon-degrading bacteria]

The storage in the laboratory of hydrocarbon degrading bacteria to be used in the decontamination of polluted sites or in the enhancement of biological treatment of industrial effluents was studied. Storage was carried out at 4 degrees C in nutrient agar and in a medium with selection pressure, liquid mineral medium with hydrocarbons. Storage at 4 degrees C with selection pressure and storage at -20 degrees C of 7 gram negative bacilli were compared. The former was the easiest method for preserving the greatest number of strains viable and active.