Journal of Global Ecology and Environment

Spent mushroom substrate (SMS) and Costus afer bagasse (CAB) are abundantly available agro-wastes in the Niger Delta region of Nigeria and may serve as cost-effective amendments for the remediation of petroleum hydrocarbon-contaminated soils. This study evaluated the bioremediation potential of SMS and CAB applied at three amendment rates (0.5, 1.0, and 1.5 kg) to sandy-loam soil contaminated with Bonny Light crude oil at low, medium, and high contamination levels (250 g, 500 g, and 750 g per 10 kg soil, respectively) over a 120-day period. Treatment performance was assessed using total petroleum hydrocarbon (TPH), total polycyclic aromatic hydrocarbon (TPAH), and total monocyclic aromatic hydrocarbon (TMAH) concentrations. Statistical analyses, including analysis of variance (ANOVA) and multiple linear regression, were conducted using Minitab® v19 at a 95% confidence level. Results indicated significant reductions (p < 0.05) in hydrocarbon concentrations across all amended treatments relative to the control. The highest remediation efficiency was achieved with 1.5 kg SMS (T4), recording TPH reductions of 93.20%, 89.80%, and 87.16% under low, medium, and high contamination levels, respectively. Although treated soils met Nigerian regulatory intervention limits, residual concentrations remained above target values. Overall, SMS demonstrated greater remediation efficiency than Costus afer bagasse. These findings suggest that locally available agro-wastes, particularly SMS, can significantly reduce the cost and duration of bioremediation of crude oil-contaminated soils in the Niger Delta.