Possible Uses of Wastewater Sludge to Remediate Hydrocarbon-Contaminated Soil

Abstract

Mexico is one of the most important producers of petroleum in the world. According to the Economist (2009) it was ranked 6th in the world in 2006. Consequently, in areas surrounding drilling sites and during transport contamination occurs frequently. Although autochthonous microorganisms in any given ecosystem are well capable of degrading petroleum (Grant et al., 2007), different techniques, such as phytoremediation, bioaugmentation or biostimulation, have been applied to accelerate removal of hydrocarbons and reduce the residual concentration (Fernandez-Luqueno et al., On line). Cultivation of plants in a petroleum contaminated soil or phytoremediation is known to accelerate removal of hydrocarbons from soil, but not always (Barea et al., 2005; AlvarezBernal et al., 2007). Bioaugmentation or the application of microorganisms to soil that are capable of degrading petroleum components should normally accelerate removal of hydrocarbons, but their low mobility and survival in soil often hamper dissipation of the contaminants (Bouchez et al., 1999; Teng et al., 2010). Biostimulation or the application of organic wastes to a contaminated soil is the easiest and most forward way to accelerate removal of hydrocarbons from soil (Scullion, 2006; de Lorenzo, 2008). Urban wastewater was traditionally discarded in rivers contaminating the environment, although that apart from pathogens, the effect on the ecosytems was not excessive. With the onset of the industrial revolution, these practices become less and less sustainable as chemical contamination altered the river ecosystems. Treatment plants were used to treat the wastewater avoiding contamination of the surface water, but generating large amounts of wastewater sludge. This wastewater sludge was often used in agricultural practices, but its large heavy metal content and organic contaminants often limited its use. In Mexico, urban wastewater is generally low in chemical contaminants and heavy metal content, although exceptions do exist, e.g. wastewater generated in the tanneries of Leon contains large amounts of Cr (Contreras et al., 2004). In Mexico, however, wastwater sludge often contains pathogens that restrict its use in agricultural practices (Franco-Hernandez et al., 2003). For instance, wastewater sludge obtained from the treatment plant in Lerma contained 30×103 viable eggs of helminthes. Consequently, the sludge can not be applied to arable land, but it can be applied to soil that is not used for agricultural practices, e.g. remediation of contaminated soil (USEPA 1994, 1999). This study reports on the effect wastewater sludge has on the removal of hydrocarbons from soil. Anthracene, phenanthrene or benzo(a)pyrene, recalcitrant polycyclic aromatic hydrocarbon, (PAHs), that are toxic to humans (Cai et al., 2007) were used as models in this study.