Synergistic bioremediation of crude oil–contaminated soil using cattle rumen waste and Trichoderma harzianum on hydrocarbon degradation and soil fertility dynamics

Crude oil-related pollution poses a significant threat to ecosystem health and soil productivity. Trichoderma harzianum, a biocontrol fungus, is known for its ability to suppress pathogens and detoxify contaminated environments. This 12-week laboratory incubation study investigated the synergistic potential of T. harzianum combined with cattle rumen waste to enhance bioremediation of crude oil-contaminated soil. Two forms of cattle rumen waste (wet and dry) were applied at 10 t ha−1 and inoculated with varying volumes of T. harzianum (0, 2.5, 5, and 10 mL), resulting in eight treatment combinations. Key soil parameters (pH, available phosphorus (P), total nitrogen (TN), and total hydrocarbon content (THC)) were monitored. T. harzianum inoculation increased soil pH from 7.0–7.5 (neutral) to 7.9–8.2 (moderately alkaline) and stimulated hydrocarbon-degrading microbial populations. Reductions in TN and available P reflect microbial assimilation during hydrocarbon catabolism. THC degradation was dose-dependent and most effective with higher inoculum volumes, following: T10Rd (87.6%) > T10Rw (87.2%) > T5Rd (76.9%) > T5Rw (69.1%) > T0Rd (69.0%) > T0Rw (66.9%) > T2.5Rd (61.3%) > T2.5Rw (45.1%). These findings demonstrate that cattle rumen waste at 10 t ha−1, especially when combined with 5–10 mL of T. harzianum, significantly enhances bioremediation efficiency while dynamically modulating soil fertility parameters.