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DETERMINATION OF OIL & GREASE IN WASTEWATER

Laboratory Testing Form – Engineers India Solutions
Test: Determination of Oil and Grease in Wastewater
Field: Environmental Engineering / Wastewater Quality Testing

1. Objective

To determine the concentration of oil and grease present in a wastewater sample by solvent extraction and gravimetric measurement. Oil and grease testing is important for assessing wastewater quality, industrial effluent characteristics, treatment efficiency, and potential environmental pollution.

2. Principle

Oil and grease present in wastewater are extracted using a suitable organic solvent. The solvent dissolves extractable oils, fats, grease, and other non-polar substances. After extraction, the solvent is removed by evaporation, leaving the extracted residue. The mass of this residue is determined gravimetrically and reported as mg/L of oil and grease.

3. Apparatus and Materials

• Wastewater sample

• Separatory funnel

• Measuring cylinder

• Analytical balance

• Clean extraction vessel/flask

• Evaporation apparatus

• Filter or suitable separation equipment

• Organic extraction solvent appropriate to the laboratory's approved method

• Distilled water

• Sample collection bottle

• Personal protective equipment (PPE)

4. Sample Collection

Collect a representative wastewater sample in a clean, suitable container. Avoid unnecessary agitation that may cause loss or alteration of oil and grease. The sample should be preserved, transported, and analyzed according to the applicable laboratory method and specified holding-time requirements.

5. Testing Procedure

1. Measure a known volume of well-mixed wastewater sample, for example 1 litre.

2. Transfer the sample to a suitable separatory funnel.

3. Add the specified quantity of extraction solvent according to the approved laboratory method.

4. Stopper the separatory funnel securely and mix carefully.

5. Allow the mixture to separate into aqueous and solvent layers.

6. Drain the appropriate layer and collect the solvent extract.

7. Repeat the extraction as required by the selected standard method to improve recovery.

8. Combine the solvent extracts in a clean, pre-weighed extraction vessel.

9. Remove the solvent by controlled evaporation using appropriate laboratory equipment.

10. Allow the vessel and remaining residue to cool in a controlled environment.

11. Weigh the vessel containing the extracted residue.

12. Determine the mass of oil and grease by subtracting the tare mass of the clean vessel.

13. Record all observations and calculate the concentration in mg/L.

6. Laboratory Observation

ParameterObservationSample Volume1000 mLEmpty Extraction Vessel52.684 gVessel + Extracted Residue52.721 gMass of Oil & Grease0.037 gTest Temperature25°C

7. Calculation

Mass of extracted oil and grease:

52.721 − 52.684 = 0.037 g

Convert to milligrams:

0.037 g × 1000 = 37 mg

For a 1-litre sample:

Oil & Grease = 37 mg / 1 L

Result = 37 mg/L

8. Test Result

The concentration of oil and grease in the tested wastewater sample is 37 mg/L.

The result should be compared with the applicable discharge standard or project-specific requirement for the relevant wastewater source.

9. Quality Control and Precautions

• Use clean, dry and properly conditioned glassware.

• Avoid contamination from lubricants, oils, hands, or laboratory equipment.

• Use a method-approved extraction solvent and follow its safety requirements.

• Perform blank and quality-control checks as required by the laboratory's analytical method.

• Ensure complete phase separation during extraction.

• Avoid loss of extracted material during solvent transfer.

• Ensure that solvent evaporation is complete before final weighing.

• Use a calibrated analytical balance.

• Handle organic solvents inside appropriate ventilation equipment.

• Wear suitable PPE throughout the test.

10. Conclusion

The oil and grease content of the wastewater sample was determined using a solvent extraction and gravimetric laboratory procedure. Based on the illustrative observations, the measured concentration was 37 mg/L. Accurate sampling, extraction, weighing, contamination control, and quality assurance are essential for obtaining reliable wastewater laboratory results.

Note: The numerical values provided are illustrative. Actual laboratory reports should contain the measured values obtained using the applicable approved standard method.

Note: According to Pollution Control Board (PCB) standards, the maximum permissible limit for oil and grease in wastewater is typically10{ mg/L}