Bioremediation of Crude Oil-Polluted Soils Using Cassava Peels and Sawdust as Biostimulants

Petroleum hydrocarbon contamination of soils is a persistent problem in many oil-producing regions, where conventional remediation methods are often too costly or impractical to implement. Biostimulation using locally available organic materials offers a simple and sustainable alternative. In this study, cassava peels and sawdust were evaluated as low-cost agro-waste amendments for the remediation of crude oil–polluted soil. The materials were applied individually and in combination (1:1 ratio) and incubated for 56 days. Soil samples collected on Days 0, 28, and 56 were analyzed for extractable total petroleum hydrocarbons (ETPH), nickel (Ni), cadmium (Cd), and pH. Only minor natural attenuation was observed in the untreated polluted soil, with about 1% ETPH reduction after 56 days. In contrast, cassava peels and sawdust enhanced hydrocarbon degradation, achieving ETPH reductions of 23.1% and 18.7%, respectively. The combined treatment produced the largest reduction (38.6%) and resulted in among the lowest residual Ni and Cd concentrations. Soil pH in amended treatments remained near neutral, creating conditions favorable for microbial activity. Overall, the findings show that agro-waste materials can effectively improve bioremediation performance and provide a practical, low-cost option for managing crude oil–contaminated soils, particularly in resource-limited settings.