Multimedia fate of petroleum hydrocarbons in the soil: Oil matrix of constructed biopiles

Abstract

A dynamic multimedia fugacity model was used to evaluate the partitioning and fate of petroleum hydrocarbon fractions and aromatic indicator compounds within the soil: oil matrix of three biopiles. Each biopile was characterised by four compartments: air, water, soil solids and non-aqueous phase liquid (NAPL). Equilibrium partitioning in biopile A and B suggested that most fractions resided in the NAPL, with the exception of the aromatic fraction with an equivalent carbon number from 5 to 7 (EC(5-7)). In Biopile C, which had the highest soil organic carbon content (13%), the soil solids were the most important compartment for both light aliphatic fractions (EC(5-6) and EC(6-8)) and aromatic fractions, excluding the EC(16-21) and EC(21-35). Our starting hypothesis was that hydrocarbons do not degrade within the NAPL. This was supported by the agreement between predicted and measured hydrocarbon concentrations in Biopile B when the degradation rate constant in NAPL was set to zero. In all scenarios, biodegradation in soil was predicted as the dominant removal process for all fractions, except for the aliphatic EC(5-6) which was predominantly lost via volatilization. The absence of an explicit NAPL phase in the model yielded a similar prediction of total petroleum hydrocarbon (TPH) behaviour; however the predicted concentrations in the air and water phases were significantly increased with consequent changes in potential mobility. Further comparisons between predictions and measured data, particularly concentrations in the soil mobile phases, are required to ascertain the true value of including an explicit NAPL in models of this kind.

Mobility of total petroleum hydrocarbons in Shambat soil in Sudan

“…At the depth of 5 cm, Decane was detected after two days and in 10 cm after 28 days under 0.32 ppm crude oil treatment. These findings agreed with that reported by Coulon et al (2010) who concluded that the mobility of hydrocarbons fractions in the soil was governed by its leaching factors (special parameters of hydrocarbons) which were very high in Decane and Undecane hydrocarbon fractions. Figure 3 shows the percent recovery of Tridecane at different soil depths under different crude oil treatments and different intervals of time.…”

Molecular dynamic simulation of asphaltene co-aggregation with humic acid during oil spill

“…It is known that asphaltenes prefer to aggregate in aqueous and organic solvents, which results in porous networks sequestrating small oil molecules (Li et al, 2012b). Large scale aggregation of asphaltenes is adverse for oil removal because it (i) alters the surface hydrophobicity and increases the mass transfer resistance for the release of light oil fractions during physical removal, and (ii) forms a thick and viscous non-aqueous phase liquid hindering the biodegradation due to the lack of water, oxygen and nutrients (Coulon et al, 2010). Although various numerical models have been developed to predict oil fate such as the Monte Carlo based nonlinear dynamic program (Li et al, 2014), the lattice Boltzmann based large-scale oil spill model (Maslo et al, 2014) and the Eulerian-Lagrangean cross-scale oil spill model (Azevedo et al, 2014), the effects of asphaltene aggregation on the overall environmental risks were not well incorporated into these models.…”

Insights into asphaltene aggregation in the Na-montmorillonite interlayer

“…The adsorption and aggregation of asphaltenes on mineral surface would result in a thick and viscous non-aqueous phase liquid (NAPL). Previous studies indicated that the NAPL was the most dominant compartment for the distribution of petroleum hydrocarbons (Coulon et al, 2010) and the retention time of PAHs in the NAPL was at least 3-fold longer than in the others phases (Pollard et al, 2008). Therefore, drawing on a comprehensive understanding of asphaltene aggregation on the clay surface is of particular interest for developing a realistic environmental risk assessment framework for oil contaminated soils.…”