Straw-assisted self-sustained smoldering remediation of low-concentration petroleum hydrocarbon-contaminated soils

Self-sustained smoldering is promising for soil remediation yet fails in soils with low petroleum hydrocarbon concentrations (LPHCs) due to insufficient heat generation. This study proposes a straw-assisted smoldering strategy to overcome this limitation. First, the combustion performance of rice, corn, soybean, and wheat straws was evaluated via thermogravimetric analysis. Subsequently, smoldering experiments were carried out to systematically examine the smoldering characteristics of LPHC-contaminated soils blended with straws at different mixing ratios. Finally, an analytic hierarchy process (AHP)-based evaluation framework integrating cost-effectiveness, remediation efficiency, and sustainability was innovatively developed for comprehensive assessment of different straw-mixing strategies. Thermogravimetric results revealed that rice and wheat straws exhibited superior combustion characteristics. All straws successfully enabled smoldering in LPHC-contaminated soil. The smoldering velocity varied significantly with straw types and mixing ratios. Increasing the straw-blending ratio from 1:30 to 1:20 decreased the smoldering velocity by approximately 18% for rice and wheat straw blends, but increased it by 56.6% and 22.6% for corn and soybean straw-blended soils, respectively. The novelty of this study is that APH evaluation identified a 1:30 rice straw-blending ratio as the optimal strategy for smoldering remediation, which had a 92.2% PHC removal efficiency verified through gas chromatography (GC) testing. These findings provide reliable technical support and key parameter benchmarks for the engineering application of smoldering remediation in LPHC-contaminated soils.