Comparative enzyme kinetics of catalase and dehydrogenase under municipal waste and CaO treatments in spent engine oil polluted soil

This study investigates the comparative enzyme kinetics of catalase and dehydrogenase in spent engine oil (SEO)-polluted soil amended with municipal organic waste and calcium oxide (CaO). Using a Latin square design, contaminated soils were treated and monitored over 70 days. Enzyme kinetics were modeled via Michaelis-Menten and Lineweaver-Burk approaches, with kinetic parameters (Vmax and Km) determined at seven time points. On Day 1, dehydrogenase showed the lowest Km under municipal waste treatment (0.182 mM), indicating high substrate affinity, while CaO-treated soils exhibited the highest Km (0.645 mM). Vmax for dehydrogenase peaked on Day 14 in control (1.145 μg TPF g⁻¹ h⁻¹), followed by municipal waste (1.103) and CaO (0.860). Catalase exhibited lower Km values throughout the study, with early activity suppressed (Vmax ~0.076–0.086 μmol H₂O₂ min⁻¹ g⁻¹) but rising significantly by Day 42 (Vmax ~1.111 across treatments). Catalytic efficiency (Vmax/Km) revealed that municipal waste consistently enhanced enzyme activity, particularly in the early remediation phase. By Day 70, enzyme kinetics stabilized, with Km and Vmax values converging across treatments: dehydrogenase Km ~4.13 mM, Vmax ~0.71; catalase Km ~4.12 mM, Vmax ~0.71. Statistical analysis showed no significant differences (p > 0.05) among treatments at Day 70. These findings affirm that enzyme kinetics are reliable indicators of bioremediation efficiency and demonstrate that municipal waste, owing to its microbial and nutrient-rich profile, provides superior enhancement of enzymatic activity compared to CaO in remediating SEO-contaminated soils.