Abstract: Waste drilling slurry is one of the main pollutants generated during oilfield drilling operations, and improper disposal can pose a threat to surrounding soil and groundwater. In this study, modified biochar was used as a carrier to immobilize the selected highly efficient composite degradation microbiota. The modified biochar material exhibited excellent porous properties and abundant surface functional groups, enabling high efficiency in microbial loading. During the 63-day remediation period, the degradation rates of COD, TOC, and NH4+-N in waste slurry by NaOH-EP@Bacteria were 81.09%, 65.86%, and 83.27%, respectively. Enzyme activity assays and high-throughput sequencing revealed that, compared to other treatment groups, NaOH-EP@Bacteriaexhibited higher microbial species abundance and activity in the rehabilitated soil, which had a positive impact on enhancing microbial tolerance and organic matter degradation efficiency. This study followed the principle of treating waste with waste and provided a low-cost and effective method for using abandoned wheat straw to prepare immobilized microorganisms material to remediate waste drilling slurry. It opened a new way to solve the pollution of abandoned drilling slurry in oil fields.

Key words: modified biochar, immobilized microorganisms, waste drilling slurry, soil remediation