To determine the quantity of oil and grease present in the given sample of water by partition gravimetric method.
The oil and grease contents of domestic and certain industrial wastes and the sludge, is of an important consideration
in the handling and treatment of these material for ultimate disposal. Knowledge of the quality of the oil and grease
present is helpful in proper design and operation of wastewater treatment system. The term grease applies to wide
variety of organic substance that is extracted from aqueous solution or suspension by hexane. Hydrocarbons,
esters, oils, fats, waxes and high molecular weight fatty acids are the major materials dissolved by hexane. All these
material have a greasy feel and are associated with the problems in wastewater treatment related to grease.
Three methods by which oil and grease are estimated are (i) the partition-gravimetric method
(ii) partition infrared method, and (iii) the solvent extraction method. Though method (i) does not provide needed
precision, it is widely used for routine analysis of samples with high oil and grease contents because of its simplicity
and no need of special instrumentation. In method (ii) adequate instrumentation allows for the measurements of as
little as 0.2 mg oil and grease. Method (iii) is identical to gravimetric method but it is designed for the samples that
might contain volatile hydrocarbons that otherwise would be lost in the solvent removal operation of gravimetric
In the Partition-Gravimetric method, dissolved or emulsified oil and grease is extracted from water by intimate
contact with trichlorotrifluoroethane; petroleum ether (40/60) or hexane.
- Separating funnel
- Distilling flask
- Vacuum pump.
Reagents (» click to check the preparation of reagents)
- Trichlorotrifluosoethane (freon).
Collect about 1 litre of sample and mark sample level in bottle for latter determination of sample
volume. Acidity to pH 2 or lower; generally, 5 ml HCl is sufficient. Transfer to a separating funnel.
Carefully rinse sample bottle with 30 ml trichlorotrifluoroethane and solvent washing to separating
Preferably shake vigorously for 2 minute. However, if it is suspected for stable emulsion shakes gently
5 to 10 minute.
Let layer separate out, drain solvent layer through a funnel containing solvent– moistened filter paper
into a clean, evacuated distilling flask. If a clear solvent layer cannot be obtained, add 1g Na2SO4,
Extract twice more with 30 ml solvent each time but first rinse sample container with solvent. Combine
extracts in evacuated distilling flask and mash filter paper with an additional 10 ml to 20 ml solvent.
Distill solvent from distilling flask in a water bath at 70°C. Place flask on water bath at 70°C for
15 minute and draw air through it with an applied vacuum for final 1 minute after the solvent has
evaporated. If the residue contains visible water, add 2 ml acetone evaporates on a water bath and
repeat the addition and evaporation until all visible water has been removed. Cool in a desiccators
for 30 minute and weigh it.
No known solvent will dissolve effectively only oil and grease. Solvent removal results in the loss of short chain
hydrocarbon and simple aromatic compound by volatilisation, and heavier residual of some effluents may contain
significant portion of material that are not extracted with the solvent.
Temperature of measurement = .............°C
Mass of evacuated flask = .............g
Mass of evacuated flask + residue = .............g
Mass of residue = .............mg
Volume of sample = .............mL
The amount of oil and grease in the sample can be calculated as,
Oil and Grease (mg/L) = (A - B) 1000/volume of the sample
A = mass of evacuated flask and residue (g)
B = mass of evacuated flask (g)
The amount of oil and grease in given water sample = .............mg/L.