A test method for determining the oil concentration in water samples contaminated with oil and grease

ABSTRACT Oil and grease concentration in water samples contaminated by oily residues can be determined by the procedures established in the Standard Methods for the Examination of Water and Wastewater. However, its application does not always result in adequate values or satisfactory accuracy levels in order to meet regulatory standards. In this sense, this paper presents a test-method proposal for determining mineral oil concentration in water samples from runoff of paved areas subject to oil and grease spillages. This method is based on the partition-gravimetric method (5520 B) established by the Standard Methods. In the new procedure, the separation between the extraction solvent containing residues and the aqueous phase remainder was replaced by the whole water sample evaporation in an oven at 85ºC. In order to assess the proposed method’s efficiency, samples were prepared with known oil concentrations of 200, 100, 50, 25 and 15 mg.L-1, in distilled water and laboratory tests were performed to determine the oil content, according to the new procedure. The values obtained for the oil concentrations through the proposed procedure are quite satisfactory, presenting linear behavior in relation to the reference concentrations. This fact evidences the reliability of the new method and its applicability in determining the oil concentration in contaminated water samples from runoff in pavement surfaces.