Remediation of phenol-contaminated soil using iron sludge-Salix psammophila composite biochar-immobilized microorganisms

Using iron-rich sludge and Salix psammophila biomass as raw materials, iron sludge biochar (FB), Salix psammophila biochar (SLB) and iron sludge-Salix psammophila composite biochar (SFB) were prepared by pyrolysis. The adsorption capacities of the three types of biochar for phenol and phenol-degrading bacteria were tested. SFB was selected as the carrier for microbial immobilization and a comparative study was conducted to assess the remediation efficiency of phenol-contaminated soil using three approaches: bioaugmentation with SFB-immobilized microbes (SFB-BA), bioaugmentation with free microbes (BA), and natural attenuation (NA). The results showed that SFB exhibited superior properties, including a higher carbon content (24.88%) compared to FB, a large specific surface area (90.046 m²/g), a magnetic property (27.13 A·m²/kg), as well as a strong phenol adsorption capacity (8.71 mg/g) and microbial immobilization effect (2.73×10⁸ CFU/g). SFB-BA treatment achieved a phenol degradation rate approximately 2.5 times that of the NA group. It can also provide a niche for exogenous and indigenous microorganisms, which causes less perturbation to the soil micro-ecosystem compared to the BA treatment, thereby offering dual advantages of effective contaminant remediation and ecosystem stability preservation. Using SFB-immobilized microorganisms to enhance soil organic pollution remediation is thus a technology with broad application prospects.