Graciela Isabel Vecchioli

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.

Extent of cleaning achievable by bioremediation of soil contaminated with petrochemical sludges

Bioremediation is capable of reducing the hydrocarbon concentration of contaminated soil by 75-95% depending on the soil type, the kind of hydrocarbons and the history of the contamination. The impact of different number of petrochemical sludge applications to soil on the degree of PAH elimination was assessed. A simple and reliable extraction and gas chromatographic method was used to facilitate more rapid determination of hydrocarbon contamination in soils and sludge wastes. Its application in a model laboratory bioremediation experiment and a pilot field study were used to illustrate its practical benefits. Post-remediation persistence of sludge constituents was evaluated after a single dose sludge application in the laboratory and after seven sludge applications in the field. A relative increase in the concentration of some PAHs was detected at the end of the experiments, but their individual concentrations were reduced to suggested values for industrial soils. The remaining concentration of total hydrocarbons in soil was found to be similar in both experiments, pointing to soil organic matter adsorption capacity as the factor determining hydrocarbon elimination limits in soil bioremediation.

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 storage on the toxic potential of hydrocarbon containing sludges

In many cases, petroleum‐derived sludges are stored in open air ponds. In this condition, weathering may produce changes that can be important when choosing a treatment and/or disposal method. The effect of weathering on chemical and toxicological characteristics of sludges were studied in two different sludges, one from a petrochemical API‐separator (API2N) and the other from a refinery biological treatment unit. Starting determinations were performed with end‐of‐the‐pipe composite samples. Determinations were repeated after a 6‐month weathering period. Physico‐chemical characterization included pH, water content, extractable organics, and class fractionation into aliphatics, aromatics, and asphaltics. Microbiological concentration was done by enumeration of viable bacteria in plate count agar and solid mineral medium with the sludge as the only source of carbon and energy, and fungi in Cooke rose bengal agar. For toxicological assessment a battery of bioassays was performed that included: Bacillus cereus spot test, Resazurine reduction test, Bioluminiscence test with Photobacterium, effects on viable soil bacteria counts, Latuca sativa seed germination and root elongation test. The Ames test (TA‐98 with S9 microsomal activation) was used to assess genotoxicity changes. Comparison of starting results of both sludges with those obtained after 6 months showed a minimal change in the chemical characteristics, a significant increase in the starting low level of bacteria in API2N, reduction in acute toxicity and increase in the mutagenic effect in the dimethyl sulfoxide (DMSO)‐sludges fraction, but not in the DMSO‐ethylether organic fraction in both sludges. ©1999 John Wiley & Sons, Inc. Environ Toxicol 14: 227–233, 1999