Abstract: Removal of polycyclic aromatic hydrocarbons (PAHs) from soils can be enhanced by inoculation of cold-tolerant mixed strains (SDR4+JDR7) at low temperature. However, the inoculated strains would get lost rapidly, being poor repeatability. Microbial immobilization technique can overcome these drawbacks to some extent. With affinity to microorganisms, adsorption ability, and bioavailability of enriched contaminants as the three important factors for the selection of immobilization carriers, corn cob (Y), peanut shell (H), vermiculite (Z) and peat soil (N) were chosen as the carriers to adsorb and immobilize the mixed strains that are highly effective to degrade PAHs. Degradation of phenanthrene (Phe), pyrene (Pyr), and benzo(a)pyrene (BaP) in the contaminated soil was examined, and Michaelis-Menton and Mond kinetic models were applied to fit the degradation results. All the immobilized strains with the four carriers Y-(SDR4+JDR7), H-(SDR4+JDR7), Z-(SDR4+JDR7), N-(SDR4+JDR7)) had better remediation abilities than the free strains after 60 days. Among them, Z-(SDR4+JDR7) presented the best degradation abilities, with removals of Phe, Pyr and BaP being 64.38%, 48.71% and 40.19%, respectively; followed by Y-(SDR4+JDR7) with removals being 58.49%, 45.91% and 37.07%, respectively. The degradation rate of Phe by Y-(SDR4+JDR7) was the highest, which was 0.60 d^-1, 7.7% higher than that by the free strains. Z-(SDR4+JDR7) showed the highest degradation rates of Pyr and BaP, which were 0.54 and 0.20 d^-1, respectively, with 11.83% and 10.85% increases compared to the corresponding free-living bacteria. Z-(SDR4+JDR7) had the shortest half-life of the high-ring BaP degradation, which was 86.64 d. Our results can provide reference for remediation of PAHs contaminated soil in northern China with cold climate.

Key words: Na₂WO₄, apple, ¹⁵N absorption and utilization, ¹³C accumulation, fruit quality