Biodegradation of Soybean and Castor Oil Biodiesel: Implications on the Natural Attenuation of Monoaromatic Hydrocarbons in Groundwater

Abstract

The potential groundwater impacts of biodiesel releases have received limited attention despite the increasing probability of such events. In this work, microcosms were prepared with unacclimated sediment and groundwater from the Ressacada Experimental Site (Florianopolis, Santa Catarina, Brazil) and spiked with 54.8 mg/L of pure soybean or castor oil biodiesel (B100). Oxygen was purged from the microcosms to mimic commonly anoxic and hypoxic conditions at fuel‐impacted sites; low background concentrations of nitrate (1.2 to 2.5 mg/L) and sulfate (2.2 to 3.0 mg/L) were present. Biodegradation was assessed by the removal of fatty acid methyl esters and hydrocarbon components relative to sterile controls. Approximately 80% of soybean biodiesel was biotransformed in 41 d, compared to only 40% of castor oil biodiesel removed in 90 d. The higher persistence of castor biodiesel was attributed to its higher viscosity and lower bioavailability. Additional microcosms were prepared similarly to assess the impact of biodiesel on hydrocarbon degradation. These microcosms were spiked with benzene (2.9 mg/L) and toluene (0.8 mg/L) with or without soybean biodiesel (54.8 mg/L). The biodiesel had an inhibitory effect, increasing the time required to remove toluene from 25 to 34 d. Similarly, 45% of benzene was removed in the presence of biodiesel within 34 d, compared to 90% in the absence of biodiesel. Overall, we postulate that the relatively high viscosity of biodiesel is conducive to limited migration potential and a smaller but longer lasting inhibitory region of influence, compared to that exerted by more soluble, more mobile, and readily degradable biofuels such as ethanol. However, controlled release studies are needed to test this hypothesis and characterize the complex dynamics of such releases.

Influence of the Anaerobic Biodegradation of Different Types of Biodiesel on the Natural Attenuation of Benzene

“…In addition, limited research has been done to examine the impact of biodiesel on the anaerobic biodegradation of benzene. Previous work on the influence of biodiesel on anaerobic benzene biodegradation showed the negative impact of one type of bio-diesel (soybean biodiesel) but did not monitor for methane production or test other biodiesel sources (Corseuil et al 2011b). Another work monitored for methane production but did not identify the source of biodiesel in the B20 blend (Ramos et al 2013).…”

“…However, depending on the characteristics of the site and the amount spilled, anaerobic conditions may prevail over the aerobic ones. Al-though this is the case, few studies exist on the anaerobic biodegradation of biodiesel (Aktas et al 2010;Corseuil et al 2011b;Lapinskienne and Martinkus 2007;Ramos et al 2013;Sorensen et al 2011).…”

“…One recent study examined the efficacy of ammonium acetate for the biostimulation of anaerobic BTEX removal in the field at a B20 contaminated site (Ramos et al 2013). Corseuil et al (2011b) studied the use of soybean and castor bean oil biodiesel and found that unsaturated/less viscous bio-diesel tends to be more easily degraded; however, it is not known whether other types of biodiesel will show similar behavior. In addition, limited research has been done to examine the impact of biodiesel on the anaerobic biodegradation of benzene.…”

“…Anaerobic benzene degradation is important due to its presence in fuel hydrocarbons, toxicity, and the difficulty in its degradation under methanogenic conditions (Da Silva and Alvarez 2004;Edwards et al 1992;Grbic-Galic and Vogel 1987). It is, however, expected, that the anaerobic biodegradation of different types of biodiesel and the resulting impact on benzene degradation presents a high degree of complexity (Corseuil et al 2011b;Sorensen et al 2011).…”

“…On the few existing studies on anaerobic conditions (Aktas et al 2010;Corseuil et al 2011b;Lapinskienne and Martinkus 2007;Ramos et al 2013;Sorensen et al 2011), some focused on evaluating the degradation in terms of LCFA (long-chain fatty acids), nitrates, and sulfates (Corseuil et al 2011b;Liu and Suflita 1994), and also on biodiesel impacts, for example, on metal corrosion (Aktas et al 2010). One recent study examined the efficacy of ammonium acetate for the biostimulation of anaerobic BTEX removal in the field at a B20 contaminated site (Ramos et al 2013).…”