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Oil and grease

 The Standard Methods for the Examination of Water and Wastewater, 24th Edition (APHA, AWWA, WEF, 2022) provides detailed procedures for analyzing oil and grease in wastewater under **Method 5520**. Below is a concise summary of the oil and grease sampling method, focusing on key aspects relevant to wastewater analysis. For precise details, refer to the official publication, as the method includes specific procedural nuances.

Overview of Method 5520: Oil and Grease

Definition: Oil and grease are defined as substances soluble in an organic extracting solvent (e.g., n-hexane or trichlorotrifluoroethane) from an acidified sample, including biological lipids, mineral hydrocarbons, and other solvent-extractable materials (e.g., sulfur compounds, organic dyes, chlorophyll) that are not volatilized during the test.

Applicability: Suitable for biological lipids, mineral hydrocarbons, and most industrial wastewaters or treated effluents. Not applicable to low-boiling fractions that volatilize below 85°C.

Sampling Method for Oil and Grease in Wastewater

1. Sample Collection:

 Container: Collect approximately 1 liter of a representative wastewater sample in a wide-mouth glass bottle pre-rinsed with the extraction solvent (e.g., trichlorotrifluoroethane or n-hexane).

Volume and Marking: Mark the sample level on the bottle to ensure accurate volume measurement.

Acidification: Immediately acidify the sample to pH ≤ 2 using concentrated hydrochloric acid (HCl) to preserve the sample and enhance extraction of emulsified or dissolved oil and grease.

Sample Type: Collect grab samples, as composite sampling is impractical due to oil and grease adhering to sampling equipment. Analyze individual samples separately to determine average concentrations over time.

Storage: Store samples at 4°C and analyze as soon as possible to minimize loss or degradation. Do not subdivide samples in the laboratory to avoid grease loss on equipment.

2. Precautions:

Avoid plastic containers, as they may adsorb oil and grease, leading to low results.

Ensure thorough mixing of the sample before analysis to capture emulsified or suspended materials.

Handle solvents carefully due to their volatility and potential health hazards; follow safety protocols outlined in the method.

Analytical Methods (Summary)

Method 5520 includes several techniques for oil and grease analysis, with the choice depending on the sample matrix and required sensitivity. The primary methods are:

5520 B: Partition-Gravimetric Method:

Extract oil and grease from the acidified sample using an organic solvent (e.g., n-hexane).

Evaporate the solvent and weigh the residue gravimetrically.

Suitable for concentrations of 4–100 mg/L

5520 D: Soxhlet Extraction Method:

  Used for samples with higher oil and grease content (20–200 mg/L).

Involves drying the sample, extracting with solvent in a Soxhlet apparatus, and weighing the residue.

5520 F: Partition-Infrared Method:

Measures oil and grease via infrared absorbance (2,980 cm⁻¹) after solvent extraction.

 Suitable for 0.5–100 mg/L and allows differentiation of petroleum hydrocarbons.[](https://ia803006.us.archive.org/24/items/gov.in.is.3025.39.1991/is.3025.39.1991.html)

Key Considerations

Solvent History: Earlier editions used petroleum ether (12th Ed.) or trichlorotrifluoroethane (14th–17th Ed.). The 24th Edition specifies n-hexane for most wastewater applications due to its effectiveness and environmental considerations.

Interferences: 

Sample complexity may cause low or high results due to co-extracted materials (e.g., organic dyes, sulfur compounds). The method lacks specificity for a single substanc

Quality Control: Prepare standards using reference oils, calibrate equipment, and follow method blanks and duplicates to ensure accuracy.

Limitations: Not suitable for volatile compounds (boiling point <85°C). Complex matrices may require additional cleanup steps.

Accessing the Method

The full details, including equipment specifications, step-by-step procedures, and calculations, are in Standard Methods for the Examination of Water and Wastewater, 24th Edition, Section 5520.

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