Integrating biochar granular with microbial fuel cell to enhance the remediation of polycyclic aromatic hydrocarbons contaminated soil

The remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil has attracted global attention. Soil microbial fuel cells (SMFC) can induce inherent electric fields to enhance pollutant removal, thereby shedding light on the remediation of PAHs contaminated soil. However, the remediation efficiency is hindered by the high internal resistance within the soil environment. This study proposed the integration of biochar granular (BCG) with SMFC to mitigate internal resistance and enhance PAHs removal efficiencies. The results illustrated that compared to SMFC, 2 % BCG-SMFC increased the removal efficiencies of phenanthrene (PHE) and pyrene (PYR) to 67.4 ± 1.5 % and 58.6 ± 1.9 %. The accompanying power density reached 44.1 mW m −2 , and this was 4.0-fold that of SMFC (11.0 mW m −2 ). Additional investigations demonstrated that adding BCG increased soil porosity and permeability. The porosity rose from 40.7 ± 3.8 % (raw soil) to 48.2 ± 0.5 % (1 % BCG soil) and 52.0 ± 0.3 % (2 % BCG soil), while permeability coefficients for 1 % BCG and 2 % BCG soils were approximately 1.27- and 1.38-fold that of raw soil (0.26 ± 0.01 mm/min). Thus, the ohmic resistance (R ohm ), charge transfer resistance (R ct ), and diffusion resistance (R d ) of the SMFCs with BCG (BCG-SMFCs) were significantly reduced, and this was beneficial for the power output and PAHs removal. Through the analysis of microbial communities, adding BCG increased the enrichment of PAHs-degrading bacteria such as Pseudomonas sp ., Lysobacter sp., Chitinophaga sp., Ralstonia sp., and Phenylobacterium sp . in BCG-SMFCs. Enzymes responsible for PAHs degradation were also highly expressed in BCG-SMFCs. This study suggested a novel approach for enhancing soil porosity and permeability by introducing BCG into SMFC, thereby improving the in situ bioremediation efficiency of PAHs contaminated soil.