ASTM D4281 Standard Test Method for Oil and Grease (Fluorocarbon Extractable Substances) by Gravimetric Determination
4. Significance and Use
4.1 A knowledge of the quantity of oil and grease present in a waste is helpful in overcoming difficulties in wastewater treatment plant operation, in determining plant efficiencies, and in controlling the subsequent discharge of these materials to receiving streams.
4.2 When oils and greases are discharged in wastewater or treated effluents, they often cause surface films and shoreline deposits.
5. Interferences
5.1 This test method is entirely empirical, and duplicate results can be obtained only by strict adherence to all details. By definition, any material recovered is called oil and grease including such things as elemental sulfur and certain organic dyes. In addition, heavier residuals of petroleum may contain a significant portion of material insoluble in the solvent used.
5.2 The rate and time of extraction in the soxhlet apparatus must be exactly as directed because of varying solubilities of different oils and greases. In addition, the length of time required for drying and cooling the extracted material cannot be varied. There may be a gradual increase in weight, presumably due to the absorption of oxygen, or a gradual loss of weight due to volatilization.
5.3 Modern industry uses a number of long-chain carbon compounds as lubricants and emulsifiers, as well as for other purposes. Often the composition of these materials differs from that of natural oils and greases, and may render them more soluble in water or more easily emulsified than the natural products. As a result, they behave as oils and greases in treatment processes and the receiving water. The procedures described here may fail to provide complete recovery of such products.
5.4 Organic based boiler and cooling water chemicals such as polymeric dispersants and chelants, antifoams, filming and neutralizing amines, and oxygen scavengers may be recovered as oil and grease when these test methods are applied to such waters.
5.5 Low-boiling fractions are lost in the solvent-removal steps of the gravimetric procedures. Even lubrication oil fractions evaporate at a significant rate at the temperature necessary for removal of the last traces of the extraction solvent. Kerosine is still more volatile and gasoline cannot be determined with any reliability by a gravimetric method.
5.6 Suspended solids may interfere by contributing to emulsions.
