Elsevier

Chemosphere

Volume 83, Issue 1, March 2011, Pages 34-40
Chemosphere

Ex situ bioremediation of a soil contaminated by mazut (heavy residual fuel oil) – A field experiment

https://doi.org/10.1016/j.chemosphere.2011.01.020Get rights and content

Abstract

Mazut (heavy residual fuel oil)-polluted soil was exposed to bioremediation in an ex situ field-scale (600 m3) study. Re-inoculation was performed periodically with biomasses of microbial consortia isolated from the mazut-contaminated soil. Biostimulation was conducted by adding nutritional elements (N, P and K). The biopile (depth 0.4 m) was comprised of mechanically mixed polluted soil with softwood sawdust and crude river sand. Aeration was improved by systematic mixing. The biopile was protected from direct external influences by a polyethylene cover. Part (10 m3) of the material prepared for bioremediation was set aside uninoculated, and maintained as an untreated control pile (CP). Biostimulation and re-inoculation with zymogenous microorganisms increased the number of hydrocarbon degraders after 50 d by more than 20 times in the treated soil. During the 5 months, the total petroleum hydrocarbon (TPH) content of the contaminated soil was reduced to 6% of the initial value, from 5.2 to 0.3 g kg−1 dry matter, while TPH reduced to only 90% of the initial value in the CP. After 150 d there were 96%, 97% and 83% reductions for the aliphatic, aromatic, and nitrogen–sulphur–oxygen and asphaltene fractions, respectively. The isoprenoids, pristane and phytane, were more than 55% biodegraded, which indicated that they are not suitable biomarkers for following bioremediation. According to the available data, this is the first field-scale study of the bioremediation of mazut and mazut sediment-polluted soil, and the efficiency achieved was far above that described in the literature to date for heavy fuel oil.

Research highlights

► First field-scale (approx. 600 m3) study of the ex situ bioremediation of mazut-polluted soil. ► 94% of the initial total petroleum hydrocarbons were biodegraded. ► 96%, 97% and 83% reductions for the aliphatic, aromatic, and NSO-asphaltene fractions, respectively. ► Confirmed biodegradation of pristane and phytane which mean that these compounds are not suitable as markers for following a bioremediation process. ► Use of zymogenous microbial consortia for re-inoculation.

Introduction

Mazut is a low quality, heavy (chain length 12–70 C atoms) residual fuel oil (ASTM D396-09a, 2009, ISO 8217, 2005). In the United States and Western Europe mazut is blended or broken down with the end product being diesel. In Eastern Europe, however, mazut is used as a source of heating fuel. The long-term storage and use of mazut can leave hydrocarbon residues in the reservoir itself, with a high content of different mechanically-derived contaminants and water in the reservoir; this can potentially lead to dangerous pollution of the living environment (particularly soil) during cleaning, when there is a serious threat to underground water.

Among numerous technologies used for cleaning up contaminated areas, the most common is bioremediation (Forsyth et al., 1995, MacNaughton et al., 1999), using zymogenous microorganisms (Langer et al., 2004). Some defined bacterial species are able to degrade, to a limited extent, all hydrocarbons present in heavy fuel oil or oil sludge (which are complex mixtures of alkanes, aromatic hydrocarbons and NSO-asphaltene fractions) (Bossert and Bartha, 1984). A consortium of microorganisms can conduct these complex processes of degradation, while at the same time, being more resistant, on average, to changes in the ecosystem than just a single microbial species (Brenner et al., 2008).

While there is significant information in the literature about the microbiological degradation of defined individual hydrocarbons (Singh and Ward, 2004), there is significantly less data about the biodegradability of some commercial petroleum products, including mazut and heavy residual fuel oil (McMillen et al., 1995, Sugiura et al., 1997, Nocentini et al., 2000, Iturbe et al., 2004, Delille et al., 2008). Studies published to date on the bioremediation of mazut and heavy residual fuel oil contaminated soils are laboratory-based, using model systems, and have indicated the potential of bioremediation for stimulated self-cleansing (Boronin et al., 1997, Díez et al., 2005).

Environmental factors play a vital role in the bioremediation of soil contaminated with heavy oil deposits (Dibble and Bartha, 1979). The most significant physical and chemical characteristics of soil which can influence the process of bioremediation are: density and water retention capacity, pH, moisture and carbonate content, temperature, availability of oxygen and carbon-based nutrients, nitrogen, phosphate and potassium, as well as the concentration of heavy metals (Rogers et al., 1993).

Although the most suitable criteria for optimizing the bioremediation process are known (control of temperature, aeration, particle size, moisture, macro and micronutrients in the mass to be composted, C/N ratio of the materials, etc. (Singh and Ward, 2004), so that the microbial activity necessary for treating this organic matter can be encouraged, very few published studies have attempted to treat mazut or heavy residual fuel oil on an industrial scale (Marín et al., 2006, Jiménez et al., 2006).

Our previous field-scale application showed that the oil pollutant mixture in the soil treated by ex situ bioremediation behaved in a complex way: different degradation rates and time evolutions were observed for fractions of the hydrocarbon mixture characterized by different molecular weights and structures (Jovančićević et al., 2008a, Jovančićević et al., 2008b, Beškoski et al., 2010). We also concluded that a stable microbial community had been formed after initial fluctuations and that the microorganisms which decompose hydrocarbons were the dominant microbial population at the end of the bioremediation process, with a share of more than 80% (range 107 colony forming units (CFU) g−1) (Milic et al., 2009).

The current study was conducted in order to determine if our previous laboratory-scale and smaller field-scale study (Jovančićević et al., 2008a, Jovančićević et al., 2008b, Milic et al., 2009) (100 m3) could be successfully up-scaled (Beškoski et al., 2010), and to determine the dynamics of field-scale ex situ bioremediation of soil contaminated with mazut, achieved by zymogenous inoculated microflora, including the degradation of differing hydrocarbon fractions.

We consider this to be the first field experiment designed to study the possibility of using bioremediation for treating a soil contaminated with heavy residual fuel oil such as mazut and mazut waste material. Key design considerations for bioremediation of soil contaminated with heavy hydrocarbons are intensive aeration achieved by mixing, biostimulation of zymogenous microbial consortia, re-inoculation of microorganisms that consume hydrocarbons and also having a control polluted soil for monitoring.

Indicators that are critical to the success of an ex situ biopile application for treatment and remediation of a heavy oil contaminated soil and that should be monitored are total petroleum hydrocarbon (TPH), moisture, pH, bulk density, water holding capacity (WHC), organic and inorganic carbon, nitrogen, available phosphorus and potassium as well as microbiological parameters such as total chemoorganoheterotrophs (TC) and hydrocarbon degraders (HD).

Section snippets

Mazut and mazut sediment-polluted soil

The mazut-polluted soil (PS) was excavated contaminated soil from an energy power plant which, due to a break-down, had been polluted with mazut and sediment from a mazut reservoir for a year.

Preparation of the zymogenous consortium of microorganisms

A consortium of microorganisms was obtained from PS by enrichment in 200 mL volumes of mineral medium (10 vol.%) (Löser et al., 1998), containing mazut (2 g L−1) as the only energy and carbon source in Erlenmeyer flasks (1 L).

Suspensions of the microbial consortium were used to seed four Erlenmeyer flasks (5 L),

Results and discussion

Key parameters for monitoring effectiveness of bioremediation are reduction of TPH and number of HD microorganisms as crucial indicators of degradation and utilization of hydrocarbons.

Acknowledgments

This work was supported by the Ministry of Science and Technological Development of the Republic of Serbia under Grant Nos. ON 142018B and TR 20131B.

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