DETERMINATION OF OIL AND GREASE IN THE WATER SAMPLE

Oil and grease are defined as any material recovered as a substance soluble in the solvent. DETERMINATION OF OIL AND GREASE includes other material extracted by the solvent from an acidified sample (such as sulfur compounds, certain organic dyes, and chlorophyll) and not volatilized during the test.

The determination of a specific substance is not measured. Rather groups of substances with similar physical characteristics are determined quantitatively on the basis of their common solubility in an organic extracting solvent.

Reagents

  • Sulfuric acid. (1:3) one part of sulfuric acid and two parts of water.
  • Petroleum ether (40°-60°C).
  • Ethyl alcohol.

Procedure

  1. Tane 200 to 250 ml of sample in a separating funnel, and add 10 ml of sulfuric acid and 25 ml of ether.
  2. Shake the sample and if suspension prevails add a small amount of ethyl alcohol. Keep it for some time to separate the two distinct layers, the upper one of the petroleum ether and the lower one of the samples.
  3. Discard the lower layer of the sample through a separating funnel.
  4. Take a pre-weighed dish or a small beaker and run the sample, the petroleum ether from the separating funnel through a filter paper that has already been moistened with fresh petroleum ether.
  5. Add a little more petroleum either through the wall of filter paper to remove any residual oil and grease on the filter paper.
  6. Evaporate the petroleum ether in a water bath and take the final weight of the dish or the beaker, after cooling in a desiccator. Never heat petroleum ether on a direct flame.

Also check Determination of Biochemical Oxygen Demand
Calculations:

DETERMINATION OF OIL AND GREASE
oil and grease determination


A = final weight of the disc
B = initial weight of the disc
V = volume of the sample taken in ml.

SAMPLE COLLECTION, PRESERVATION, AND STORAGE

Collect a representative sample in a wide mouth glass bottle that has been washed with soap, rinsed with water, and finally rinsed with solvent to remove any residues that might interface with the analysis.

Take a separate sample for the oil and grease analysis. Do not overfill the sample container, and do not subdivide the sample in the laboratory. If the analysis is to be delayed more than two hours, acidify to pH 2 or lower with 1:1 HCl and refrigerate.

For the sludge sample, the acid sample ratio is 1 ml Ha/ 80 gm of the sample, and refrigerate. Never preserve samples with CHC13 or sodium benzoate.

INTERFERENCE

  • Organic solvents have the ability to dissolve not only oil and grease but also other organic substances. Any filterable solvent-soluble substances (Exp. Oil and grease are characterized as elements of sulfur, complex aromatic chemicals, hydrocarbon derivatives of chlorine, sulfur, and nitrogen, and some organic colors) that are removed and recovered.

    There is no known solvent that can only dissolve oil and grease. A considerable amount of elements that are not solvent extractable may be present in heavier petroleum residuals.
  • Some sample matrices can increase the amount of water partitioned into the organic extraction fluid. The drying capacity of sodium sulfate can be surpassed when the extraction solvent from this sort of sample is dried with sodium sulfate, allowing sodium sulfate to dissolve and pass into the tared flask.

    Sodium sulfate crystals will be visible in the flask after drying. The sodium sulfate that passes into the flask becomes a positive interference in the gravimetric method of determination.

    If crystals are observed in the tared flask after drying, redissolve any oil and grease with 30 ml of extraction solvent, then drain the solvent through a funnel containing a clean, tared flask with a solvent rinsed filter paper Rinse the original flask two more times, then combine all of the solvents in the new flask and treat as an extracted sample.


SIGNIFICANCE

Certain constituents measured by the oil and grease analysis may influence wastewater treatment systems. If present in excessive amounts, they may interfere with aerobic and anaerobic biological processes and lead to decreased wastewater treatment efficiency.

When discharged in waste. water or treated effluents may cause surface films and shoreline deposits leading to environmental degradation.


The quantity of oil and grease present is helpful in the proper design and operation of wastewater treat¬ment systems and also may call attention to certain treatment difficulties.


In the absence of specially modified industrial products, oil and grease are composed primarily of fatty matter from animal and vegetable sources and from hydrocarbons of petroleum origin.

Knowing a sample’s relative composition reduces the complexity of pinpointing the material’s principal source and facilitates the remedy of oil and grease problems knowledge of the relative composition of a sample minimizes the difficulty in determining the major source of the material and simplifies the correction of oil and grease problems in wastewater treatment plant operation and stream pollution abatement.

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