Soil Washing for Reduction of Aromatic and Aliphatic Contaminants in Soil

Abstract

The extraction of crude oil worldwide is estimated to be about 4 billion tons annually, 10% of which leaks into the environment. Iran is in great risk of pollution because of the extensive natural oil reservoirs and the spread of the oil industry. During the past 10–15 years soil washing methods have gathered much attention due to their rapid and easy implementation and high clean up efficiencies in removing organic contaminants from polluted soils. This paper investigates the effects of soil washing at various temperatures and pH levels of the washing solutions on the removal of gasoline constituents from contaminated soils. Aliphatic and aromatic fractions of gasoline were studied for this purpose. Raw soil samples were spiked with gasoline for soil washing tests. Sodium dodecyl sulfate surfactant (with concentration of 1 g/L) was used as the washing solution for the samples. The results of this study indicate that an increase in both pH and temperature of the solution enhances the removal efficiencies of aliphatic and aromatic contaminants from soil samples. The removal efficiencies of aliphatic contaminants from coarse and fine fractions of the samples increased from 81.12 to 92.34% and 62.41 to 76.47%, as the temperature rose from 20 to 40°C, respectively. A nearly similar trend of increase was noted for the aromatic compounds. With regard to pH of the washing solutions, the removal efficiencies of the contaminants increased as the pH changed from 5.76 to 8.14. Thus, concluding that the implementation of soil washing is more efficient when the soil has naturally high pH values.

Archives of Environmental Protection

“…This is mainly due to their low operating costs and high efficiencies (Kuppusamy et al 2017). In the majority of previous studies dealing with soil washing, the liquid effluent is directed downward and crosses a fixed bed of contaminated particles (Viglianti et al 2006;Gitipour et al 2015;Saeedi et al 2019). Furthermore, laboratory-scale devices were used causing difficulties to scale up to industrial levels (Han et al 2009;Olasanmi and Thring 2020. In comparison with washing using a fixed bed of particles crossed by a descendant liquid flow, upward fluidization of the soil medium has the advantage of rupturing the soil skeleton, allowing the release of trapped hydrophobic contaminants.…”

Retrieving Oil and Recycling Surfactant in Surfactant-Enhanced Soil Washing

“…Soil contamination by petroleum-based oil is an extremely important and worldwide environmental problem. − Remediation of oil-contaminated soil is of high priority worldwide. − On the other hand, the magnitude of the issue of oil leak is large; for example, in the U.S. there are around 80,000 underground tanks currently leaking into the surrounding soil . Crude oil leaking into the environment worldwide is estimated to amount to around 0.4 billion tons annually . If the leaked oil could be retrieved and subsequently reused, it would be beneficial not only in terms of environmental remediation but also for saving resources.…”

“…Surfactant-enhanced soil washing (SESW) is one of the most versatile remediation techniques for virtually all target organic contaminants. − ,− Surfactants can reduce the oil–water interfacial tension (σ) and decrease the oil–soil attraction. SESW may be considered as a nondestructive remediation technique for the leaked oil.…”

“…SESW may be considered as a nondestructive remediation technique for the leaked oil. Unfortunately, surfactants tend to stabilize an emulsion of the oil in water (O/W emulsion) long after the SESW is performed, making it difficult to separate the oil from the water. − ,− Thus, efficient methods for demulsification of the obtained emulsions are desirable. Switchable or stimuli-responsive surfactants , have the potential to solve this problem because of their reversible interconversions between active and inactive forms in response to stimuli, which makes such surfactant-stabilized emulsions are also switchable. , CO 2 -switchable surfactants seem ideal for the SESW because CO 2 treatment leaves no obvious byproducts, but many such surfactants are cationic .…”

“…4 Crude oil leaking into the environment worldwide is estimated to amount to around 0.4 billion tons annually. 2 If the leaked oil could be retrieved and subsequently reused, it would be beneficial not only in terms of environmental remediation but also for saving resources.…”