Measurement Of Oil And Grease

Experiment 4: Measurement of Oil and Grease Introduction The partition – gravimetric method involves extraction of dissolved or emulsified oil and grease from water by using an extracting solvent. The common solvents used are n-hexane, methyl-tert-butyl ether (MTBE), and trichlorotrifluoroethane.

Any filterable solvent-soluble substances (e.g., elemental sulfur, complex aromatic compounds, hydrocarbon derivatives of chlorine, sulfur, and nitrogen, and certain organic dyes) that are extracted and recovered are defined as oil and grease. No known solvent will dissolve selectively only oil and grease. Heavier residuals of petroleum may contain a significant portion of materials that are not solventextractable.

Oil and grease has the natural tendency to float on the water surface under quiescent conditions, as the density of oil and grease is usually less than one. Not all the oil and grease is in liquid or solid form. Appreciable amounts remain in a finely divided emulsified form.

Oil and grease is an important parameter for water quality and safety. Regulatory bodies worldwide set limits in order to control the amount oil and grease entering the water reservoirs or the sea through industrial discharges and also limit the amount present in drinking water.

Objective To determine the dissolved or emulsified oil and grease in kitchen water sample by using partition – gravimetric method.

Apparatus and Materials Separatory funnel, distilling flask, liquid funnel, filter paper, distillation apparatus, waste container for used solvent, desiccator, kitchen water sample, hydrochloric acid, n-hexane, anhydrous sodium sulphate, and distilled water.

Experimental Procedure 1.

200 mL of kitchen water sample was acidified with 5 mL of HCl, and then transferred to a separatory funnel.

2.

30 mL of n-hexane solvent was added to the funnel and the mixture was shaken vigorously for 2 min.

3.

The upper solvent layer was transferred into a conical flask.

4.

The lower aqueous layer and any remaining emulsion were extracted with 2 portions of 30 mL n-hexane where the solvent layer was transferred to the same conical flask after each washing.

5.

Anhydrous sodium sulphate was added to the extract in the conical flask to absorb traces of water.

6.

The dried extract was filtered into a tarred distilling flask and then distilled at 63 – 69 °C.

7.

The remaining oil and grease in the distilling flask was cooled in desiccator and weighed.

8.

The procedures were repeated with deionized water as blank.

Result and Calculation

1. Kitchen water sample Starting temperature = 28 °C Temperature range at which = 64 – 65 °C

product was obtained Weight of empty distilling flask Weight of flask + oil and grease Weight of oil and grease

= 61.2234 g = 61.9236 g = 0.7002 g

Oil and grease

= 700.2 mg / (200/1000)L = 3501 mg / L = 3500 mg / L (to 3 significant figure)

2. Deionized water (blank)

Starting temperature = 29 °C Temperature range at which = 63 – 66 °C product was obtained Weight of empty distilling flask Weight of flask + oil and grease Weight of oil and grease

= 47.3188 g = 47.3409 g = 0.0221 g

Oil and grease

= 22.1 mg / (200/1000)L = 110.5 mg / L = 111 mg / L (to 3 significant figure)

Discussion The amount of oil and grease extracted from kitchen water sample was 3500 mg / L and that extracted from deionized water was 111 mg / L. The difference in amount of oil and grease present in these two samples was 3389 mg / L. This can be attributed to deionized water being processed whereas the kitchen water was not.

Since deionized water was being processed before, it should not contain a high level of oil and grease. The amount of oil and grease we got in blank (111 mg / L) was mainly due to the impurities such as deionized water or unevaporated n-hexane.

The temperature range at which the solvent distilled out was 63 – 66 °C, which was

nearly the boiling point of n-hexane (69 °C).

The kitchen water sample was probably taken from cafeteria. Oil and grease in kitchen water includes substances such as relatively non-volatile hydrocarbons, vegetable oils, animal fats, waxes, soaps, and greases. When measuring oil and grease gravimetrically, the substances are extracted from the sample with n-hexane, and then the n-hexane is evaporated. The residue left is weighed to determine the concentration of oil and grease materials in mg/L.

Should there be excessive discharges of oil and grease to sewerage systems, problems may occur with the clogging of sewers and pumping plants and with the interference of biological treatment processes.

Therefore, the kitchen water from cafeteria should be processed before discharged as sewage to remove oil and grease. If this kitchen water is disposed to the lake before processing, it will contaminate the lake water and affect the lake ecosystem.

The knowledge of the quantity of oil and grease present in wastewater systems is helpful in the proper design and operation of wastewater treatment systems. It is known that in the determination of oil and grease, the absolute quantity of substances with similar physical characteristics is measured quantitatively on the basis of their common solubility in an organic solvent.

Conclusion The amount of oil and grease extracted from kitchen water sample was 3500 mg / L and that extracted from deionized water was 111 mg / L. The difference in amount of

oil and grease present in these two samples was 3389 mg / L.

Reference 1.

http://www.p2pays.org/ref/02/01442.pdf

2.

http://www.freepatentsonline.com/5294553.html

3.

http://www.srcosmos.gr/srcosmos/showpub.aspx?aa=6781

4.

http://www.caslab.com/Test-Method-5520-B/

5.

http://www.astm.org/DATABASE.CART/WITHDRAWN/PS74.htm