Biodegradation of polyacyclic aromatic hydrocarbons in contaminated soil by biostimulation and bioaugmentation in the presence of copper(II) ions

The effect of a combination of biostimulation, bioaugmentation and the presence of CuSO₄ on the biodegradation of the polycyclic aromatic hydrocarbons (PAHs) dibenzofuran 210 mg kg⁻¹, benzo(a)anthracene 200 mg kg⁻¹, dibenzo-p-dioxine 100 mg kg⁻¹ and 9-fluorenone 100 mg kg⁻¹ in a sandy loam soil was studied. The pH of the soil was raised from 5 to 7 with agricultural lime. The soil was then divided into two sets labelled Treatments A and B. Six subsets numbered 1–6 were established for each of Treatments A and B. Treatment A was not amended with CuSO₄ while Treatment B was amended with 5% CuSO₄. Sterile control was established for both sets of treatment by adding 75 g sodium azide twice during the treatment period to Treatment 1. Treatment 2 was established as a natural control, without further amendments. Treatments 3–6 were tilled daily and maintained at 70% moisture. Mono-ammonium phosphate (MAP) (1 g kg⁻¹ soil) was added to Treatments 4–6 twice during the treatment period. H₂O₂ at 500 mg l⁻¹ (600 μl of a 39% solution) was added weekly to Treatment 5. A biosupplement was added to Treatment 6 every week. The experiments were incubated for 10 weeks at ambient temperature. The C:N:P ratio of the soil after the addition of MAP was 38:1:2.2. Counts of microorganisms were larger in the treatments not amended with CuSO₄. For example counts were 77×10⁶ in A6, as compared to 61×10⁶ in B6. CO₂ evolution was also consistently lower in the CuSO₄-amended treatments. Reduction in the concentrations of the PAHs in the treatments without CuSO₄ reached a maximum of 28.6% (dibenzofuran) in the sterile control and 39.1% (dibenzofuran) in the natural control. In contrast, maximum reduction in Treatment 3 reached 85% (dibenzofuran). Reduction in Treatments 4, 5 and 6 was between 90% and 100% in both Treatments A and B after 10 weeks. The combination of biostimulation and bioaugmentation (Treatment 6) enhanced PAH reduction by 100% reduction of all PAHs tested, better than only biostimulation (Treatments 4 & 5), which reduced the PAHs concentrations by between 90% and 100%. The effect of CuSO₄ on the biodegradation of the tested PAHs was more prominent during the early stages of the experiment. However, there was no significant difference in the overall residual concentrations of the PAHs in both treatments A and B at the end of the treatment period.