Improving benzo(a)pyrene biodegradation in soil with wheat straw-derived biochar amendment: Performance, microbial quantity, CO2 emission, and soil properties

Biodegradation has been identified as the most critical method to eliminate polycyclic aromatic hydrocarbons (PAHs) from soil, but its efficiency by native microbes is low and its application restricted. Therefore, to improve the biodegradation of benzo(a)pyrene (BaP, a type of PAHs) in soil, a biochar harvested from wheat straw was applied as a conditioner for soil microbial remediation. The results showed that when 2% (w/w) – 10 % (w/w) of biochar was added, the biodegradation efficiency of BaP was 35.4%–86.6%, which is much higher than that by the sole microbial remediation (23.5 %). In soil microbial remediation stimulated by biochar, the biodegradation of BaP was in good agreement with the pseudo-first-order kinetic model (R2 > 0.90), and there was a remarkable increase in the number of microbes as a result of the stimulation impact of biochar (3.3 × 109 – 1.8 × 1010 CFU/g-soil). In addition, after microbial remediation with biochar, CO2 emissions increased to 195.6–496.2 mg-C/kg-soil, soil pH increased by 0.4–1.7 units and soil organic matter content increased 2.7–9.6 fold. Meanwhile, the soil enzyme activity increased after biochar-stimulated microbial remediation, dehydrogenase activity increased by 27.5%–70.2% and polyphenol oxidase activity increased by 26.6%–69.1%. These increases suggest an improvement of soil properties. Overall, the use of biochar to promote the biodegradation of BaP in soil while simultaneously improving soil properties may be a promising method for microbial remediation of soil contaminated by PAHs.