Effects of Garden Waste Biochar Amendment on TPH Removal and Bacterial Community Restructuring in Petroleum-Contaminated Soil

Petroleum hydrocarbon contamination poses a persistent threat to soil quality and ecosystem functioning, while conventional remediation approaches are often costly and difficult to sustain over the long term. This study evaluated garden waste biochar as a sustainable amendment for the remediation of petroleum-contaminated soil and investigated its effects on TPH removal, soil physicochemical properties, and bacterial community changes. Biochar produced from garden waste at 600 °C was applied at 1% and 2% (w/w) to soil containing approximately 20,000 mg·kg−1 TPH, and changes were monitored over 360 days. High-throughput 16S rRNA gene sequencing and redundancy analysis were combined with measurements of soil properties and TPH concentrations. Compared with the petroleum-contaminated control, biochar amendment substantially enhanced TPH removal, with removal efficiencies increasing from 24.44% to 44.26% and 52.93% under 1% and 2% biochar treatments, respectively. After 360 days, TPH concentrations decreased to 10,831.68 and 9102.07 mg·kg−1 in the 1% and 2% biochar treatments, respectively. Biochar also significantly altered bacterial richness and community composition, with significant changes in the Ace, Chao1, and Sobs indices and shifts in dominant bacterial phyla. Soil nutrient availability and bacterial community structure were closely associated with environmental changes during remediation. Overall, garden waste biochar shows potential as a sustainable strategy that simultaneously promotes biomass waste valorization and petroleum-contaminated soil remediation.