Effect of nutrient and surfactant addition on polyaromatic hydrocarbon (PAH) biodegradation in contaminated soils

This investigation was carried out on soil from an oil-refinery site that was contaminated with high concentrations of polyaromatic hydrocarbons (PAHs). The aim of this work was to study the degradation of the PAHs present in the contaminated soil (with the degradation being accomplished by means of bioremediation processes), in the presence of nutrients and a surfactant, while maintaining the water content at two different levels. The study consisted of four experiments and two blanks. The experiments were prepared in six boxes, each containing 7 kg of soil, under the following conditions: B₁, contaminated soil with a 15% water content, no surfactant, no nutrients; S₁, contaminated soil with nutrients (nitrogen and phosphorus) added and a 15% water content; and S₂, contaminated soil with the addition of nutrients, a non-ionic surfactant and a 15% water content. B₂ was the same as B₁ but with a 30% water content; S₃ was the same as S₁, but with a 30% water content; and S₄ as identical to S₂, but with a 30% water content. During the degradation process, PAH concentrations were determined; the microbial population present in the soil was quantified; and respirometry tests were performed to assess the microbial activity by means of CO₂ production. The highest removal efficiency was obtained for S₄ (i.e. the sample with a 30% water content, to which nutrients and a surfactant had been added). The compounds with the best removal efficiency for all options were naphthalene and anthracene. Carbon dioxide production was also observed, indicating the presence of microbial degradation. Results indicate that several PAHs can be removed by means of bioremediation, and the process is enhanced by the addition of nutrients and surfactants.