Objective  To address the challenges of low efficiency, high costs, and secondary pollution in treating oil-contaminated sludge from oilfields, this study aims to develop a synergistic treatment technology based on plant-microbial fuel cells (P-MFC). By screening highly efficient electricity-producing bacteria and coupling them with aquatic plants, the research explores optimization pathways for the system's electricity generation performance and crude oil degradation efficiency. This work provides theoretical foundations and technical support for the resource recovery treatment of oil-contaminated sludge.

Method In this study, oily sludge from a block in Liaohe Oilfield was used as the substrate to isolate and purify a pure electrogenic bacterial strain. Combined with 16S rDNA sequence analysis and scanning electron microscopy (SEM) characterization, the strain was identified as Bacillus edaphicus, and its morphological characteristics were clarified. This strain was coupled with three aquatic plants (i.e., Jussiaea repens, Spathiphyllum kochii, and Epipremnum aureum) to construct plant-microbial fuel cells (P-MFCs). The effects of aquatic plant species and anode substrate oil content (0.1%, 1.0%, 5.0%) on the electricity generation and crude oil degradation performance of the P-MFC systems were investigated.

Result The results showed that the Jussiaea repens-P-MFC system exhibited the optimal performance: electromotive force (EMF) reached 343.2873 mV with an apparent internal resistance of 291.8 Ω, which was significantly better than those of the Spathiphyllum kochii-P-MFC and Epipremnum aureum-P-MFC systems. The crude oil degradation rate of the Jussiaea repens-P-MFC system was 29.76%, 4.28%–5.28% higher than that of the other two systems. The core reason lies in the fact that the roots of Jussiaea repens can secrete easily utilizable carbon sources and improve the sludge microenvironment. The oil content had a significant regulatory effect on system performance: the 0.1% oil content group showed the highest EMF and maximum power density; the 1.0% oil content group had the best long-term operation stability; and the 5.0% high oil content group barely produced effective electricity in the later operation stage due to the toxic inhibition of crude oil on bacterial activity. Additionally, a "electricity generation-degradation" synergetic mechanism existed in the P-MFC system.

Conclusion This study verifies the feasibility of treating oily sludge using the Jussiaea repens-Bacillus edaphicus coupled P-MFC, and reveals the principle of adapting oil content to the microenvironment regulation of plant root systems, providing crucial support for the resource-efficient treatment of high-oil-content sludge.