Crude oil (A) is treated to degrade the total petroleum hydrocarbons using a mixed population of indigenous bacteria and fungi. Reaction rate is expressed as -rA=0.04CA. Crude oil solution is fed to 250 L CSTR with 40 L/min volumetric flow rate. Initial concentration of crude oil is 1 g/kg. At time t=0, concentration of crude oil increases to 1.5 g/kg due to a technical fault. However, this fault is noticed after 4 minutes and then concentration is set to 1