Comparative Assessment of Organic–Mineral Fertilizer, Biochar, and Vermiremediation for Petroleum‐Contaminated Alkaline Soils

ABSTRACT Petroleum contamination of soils represents a major environmental challenge, especially in alkaline, clay‐rich soils where strong adsorption and nutrient limitations hinder microbial degradation. Existing remediation methods, including biochar amendment, vermiremediation, and organic‐mineral fertilizers, have shown promise individually, but their comparative effectiveness under alkaline conditions remains poorly understood. This study evaluates and compares the performance of an organic‐mineral fertilizer derived from sewage sludge, biochar, and vermiremediation using a mix of Eisenia fetida/E. andrei for remediating petroleum‐contaminated alkaline clay‐rich soils (pH 8.0–8.6). Over a 6‐month incubation, we monitored total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), dehydrogenase activity (DHA), nutrient status, changes in pseudo‐total concentrations of heavy metals, and microbial responses. Among the treatments, the organic–mineral fertilizer achieved the most comprehensive remediation, reducing TPH by up to 64% and PAHs by 59%, while enhancing microbial activity, improving nutrient bioavailability, and neutralizing soil pH. Biochar was less effective for hydrocarbon degradation but modified heavy metal concentrations and stabilized carbon, whereas vermiremediation improved DHA and nutrient cycling but showed variable hydrocarbon removal. Multivariate analyses confirmed the organic‐mineral fertilizer as the most effective strategy. These findings highlight the potential of organic‐mineral amendments for sustainable soil restoration and circular economy applications, while suggesting that future research should focus on field‐scale validation and optimization of integrated approaches combining chemical, biological, and physical mechanisms.