Firstorder model was applied to express biodegradation kinetics of waste motor oil at various initial concentrations. The first-order biodegradation rate constant was calculated using the equation: ln (Ct/C0) = kt; where, C0 and Ct represent the oil concentration at time zero and time t (%), respectively, while k and t denote the biodegradation rate constant (d1) and biodegradation time (d), respectively.