Abstract: Utilizing environmentally friendly and cost-effective microbial degradation to remove residual resin and asphaltene is crucial for the complete remediation of crude oil-contaminated soil. We investigated the effects of surfactants Tween 80 (TW), Triton X-100 (TX), and sodium dodecylbenzene sulfonate (SDBS) at concentrations of 0 (control), 5, 10, and 20 mg·kg^-1 on the degradation of resin and asphaltene in crude oil-contaminated soil by actinomycetes (Streptomyces sp. and Rhodococcus sp.). Based on an experiment with simulated soil composting degradation, we evaluated the impacts of individual and composite surfactant treatments on actinomycete biomass, the contents of total petroleum hydrocarbon (TPH), resin, asphaltene, aromatic hydrocarbon, and saturated hydrocarbon. The results showed that surfactant addition significantly enhanced actinomycete biomass and petroleum hydrocarbon degradation efficiency. Compared to that in the control, the biomass of both actinomycete strains were consistently higher in the SDBS treatments across different incubation periods. Biomass in the TX treatments was lower than in the SDBS treatments, while biomass in the TW treatments was the lowest. TPH contents in the SDBS treatments were significantly lower than those in the other treatments. Notably, in the SDBS (20 mg·kg^-1) treatment, TPH decreased from an initial 39 to 16.5 g·kg^-1 after 42 days of incubation, substantially lower than the 35.5 g·kg^-1 in the control. Among the composite treatments, the TX×SDBS combination yielded the lowest TPH contents. Specifically, in the Rhodococcus sp. experimental group under TX×SDBS treatments, TPH decreased from 39 to 16.2 g·kg^-1 after 42 days of incubation (P<0.05). Our results indicate that the application of 20 mg·kg^-1 SDBS alone or the composite surfactant combination TX (20 mg·kg^-1) × SDBS (20 mg·kg^-1) can significantly enhance actinomycete activity and promote the bioavailability and degradation efficiency of resin and asphaltene in crude oil-contaminated soil.

Key words: actinomycete, intensification, crude oil-contaminated soil, biodegradation, resin, asphaltene