Modifying the Baranyi-Roberts model for studying bio-remediation kinetics in crude-oil contaminated soil

Abstract This study investigated the application of cow bone char (CBC) and NPK fertilizer for in-situ bioremediation of crude oil-contaminated sites using a modified Baranyi-Roberts (MBR) kinetic model and a first-order kinetic model. Biodegradability potential was compared by monitoring Total Hydrocarbon Content (THC) at seven sites treated with CBC and NPK at varying doses (0.5 kg, 2.0 kg, 3.5 kg), along with a control site. For the NPK fertilizer-treated sites, the biodegradability potential increased from 0.801 to 0.936 as dosage increased from 0.5 kg to 3.5 kg while, biodegradability increased from 0.65 to 0.87 as CBC application increased from 0.5 kg to 3.5 kg in the CBC-treated sites. The bioremediation efficacy of both CBC and NPK fertilizers showed no significant difference in their performance (p-value = 0.0789) through t-test analysis. The biodegradation kinetics assessment using the modified Baranyi-Roberts (MBR) model and the first-order kinetic model yielded high correlation coefficients (above 0.98) in both CBC and NPK-treated sites. However, the MBR model, was observed to provide deeper insights into site-specific soil conditions and microbial activity, offering a more accurate assessment of bioremediation potential. A novel parameter, the hurdle number (H₀), was introduced by the MBR model to predict the readiness of a bio-stimulant to release nutrients, with H₀ = 0 in nutrient-limited soils and H₀ > 0 in nutrient-rich soils. Additionally, the activation or adaptation number (A₀) was used to assess microbial adjustment prior to active hydrocarbon degradation. In nutrient-limited soils, A₀ > 0, indicating a necessary microbial adaptation phase, whereas in nutrient-rich soils, A₀ = 0, signifying immediate microbial response without the need for prior adaptation. These findings enhance the understanding of bio-stimulant efficiency and microbial dynamics in hydrocarbon bioremediation.