Application of aerobic microorganisms in bioremediation in situ of soil contaminated by petroleum products
Introduction
In industrialized countries, contamination of soil by crude oil and petroleum products has become a serious problem. The main sources of this contamination are: oil field installations, petroleum plants, liquid fuel distribution and storage devices, transportation equipment for petroleum products, airports and illegal drillings in pipe lines. The scale of the hazards imposed on the natural environment depends on the surface of the area contaminated by petroleum products, their chemical composition, and the depth at which pollutants occur.
Crude oil and petroleum products contain many kinds of organic compounds, dominated by aliphatic and aromatic hydrocarbons (Fukui et al., 1999). The most toxic components, with mutagenic and carcinogenic potential activity, include the aromatic compounds benzene, toluene, ethylbenzene and xylene (BTEX), which easily pass into the groundwater and may pose a hazard to organisms using it (Bogan and Sullivan, 2003, Kasai et al., 2006, Wolicka and Suszek, 2008). It is commonly known that BTEX compounds are biodegradable under aerobic conditions (Nielsen et al., 2006, Sublette et al., 2006). Thus, aerobic conditions have been shown to be highly effective in the remediation of many oil spills.
Many soil microorganisms transform oil hydrocarbons into non-toxic compounds or mineralize them to inorganic compounds (Leahy and Colwell, 1990). Hydrocarbons are degraded in soil mainly by bacteria (0.13–50% of the total of heterotrophic soil microorganisms) and fungi (6–82%) (Leahy and Colwell, 1990, Wolicka, 2008). This natural microbiological activity is applied in bioremediation to reduce the concentration and/or toxicity of various pollutants, including petroleum products (Dua et al., 2002). These processes take place in the natural environment, and their end-products are carbon dioxide and water (Olliver and Magot, 2005).
Numerous microbes present in soil contaminated by oil hydrocarbons are able to grow, despite the high toxicity of these compounds. The ability to degrade and/or utilize oil hydrocarbons has been observed in numerous types of bacteria and fungi, and in yeast e.g. Candida, Saccharomyces (Bento and Gaylarde, 2001; Prenafeta-Boldu et al., 2002), some Cyanobacteria e.g. Oscillatoria, Anabaena, Nostoc, Microcoleus, Chlamydomonas, Scenedesmus, Phormidium and green algae e.g. Chlorella, Microcoleus, Chlamydomonas, Ulva, Scenedesmus, Phormidium (Antizar-Ladislao et al., 2004). However, in soil bioremediation mainly bacteria are applied, because they are distinguished by high frequency, fast growth and a wide spectrum of the utilized petroleum products. The natural environments contaminated by aromatic compounds, such as areas where oil is mined and exploited, or areas with an industrial infrastructure, create good conditions for microorganisms which can biodegrade aromatic hydrocarbons (Wolicka and Borkowski, 2007). Hence, these environments seem to be a properly for isolation of microorganisms which can be potentially applied in bioremediation in situ.
This paper is focused on the isolation and selection of aerobic consortia able to biodegrade BTEX, from an area contaminated by petroleum products, and on testing their activity under field conditions.
Section snippets
Enrichment of BTEX degrading consortia
The microorganisms were isolated from the area of a petrol station contaminated by petroleum products, located in north-eastern Poland. Contamination by BTEX in the study area has occurred for at least 30 years.
Samples of contaminated soil (ca. 5 g) were inserted in 300 ml flasks, to which a substrate with a suitable carbon source (benzene, toluene, ethylbenzene or xylene) was added as the only electron donor to the culture. The flasks were sealed with cotton wool, and then shaken in a shaker for
Selection of optimal medium for microorganisms able to biodegrade BTEX
Based on the analyses carried out at the water samples collected from the piezometers, the study area is contaminated mainly by BTEX, particularly by xylene, which occurred in the highest abundances: 5500 μg/L in P1, 5330 μg/L in P2, and 780 μg/L in P3. High concentrations of ethylbenzene were also observed in P1 (1100 μg/L) and P2 (1200 μg/L), as well as of benzene in P2 (8000 μg/L) (Table 1). The total content of bacteria in soil able to biodegrade of BTEX was 106 cfu/g d.w. of soil.
Taking into
Conclusions
- 1.
To achieve a maximal rate of BTEX biodegradation, and to minimize the introduction with the medium of different chemical compounds in the initial phase of analysis, an optimal medium was selected for the autochthonous microorganisms isolated from soil contaminated by petroleum products.
- 2.
Optimization of BTEX biodegradation in laboratory conditions provides an opportunity to obtain a high activity of the consortia able to biodegrade BTEX. The selected media should not contain simple chemical
Acknowledgement
We thank for Professor Raymond Macdonald for his help with English.
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2020, Biocatalysis and Agricultural BiotechnologyCitation Excerpt :The activity of bacteria was imbalanced in the field environment compared with laboratory condition. The environmental factors also influence the activity of bacteria and it takes longer adaptation time (Wolicka et al., 2009). The efficiency of bioremediation depends on many internal and external factors such as temperature, pH, inoculum, time of process and aeration (Srivastava et al., 2014).