Analysis of Extractable organic ( Oil & Grease) in Hazardous Waste
Oil and grease are critical parameters routinely analyzed in water, wastewater, and hazardous solid waste. These substances originate from petroleum products, lubricants, fats, oils, waxes, and industrial residues. When present in high concentrations, oil and grease can clog treatment systems, interfere with biological processes, contaminate soil and groundwater, and pose serious environmental risks.
This blog explains the principle, materials, and step‑by‑step procedure for estimating extractable organic matter (oil & grease) in hazardous waste using solvent extraction, presented in a clear and plagiarism‑free format.
Why Oil & Grease Analysis Matters
Monitoring oil and grease is essential because:
- It affects wastewater treatment efficiency
- It can inhibit microbial activity in biological systems
- It contributes to soil and groundwater contamination
- Regulatory agencies set discharge limits for compliance
For wastewater-specific methods, oil and grease are often analyzed using liquid–liquid extraction. In solid and hazardous waste, solvent extraction using hexane is widely applied.
Principle of the Method
Oil and grease are separated from the sample by solvent extraction using n‑hexane. Hexane selectively dissolves non‑polar organic compounds such as oils, fats, and greases.
Because hexane has a boiling point of approximately 40–60°C, evaporation during analysis is performed at a temperature slightly above this range to ensure complete solvent removal without decomposing the extracted organics.
The final mass increase of the extraction flask corresponds to the amount of extractable organic matter present in the sample.
Apparatus and Materials
- Analytical balance
- Vacuum pump
- Extraction thimble (filter paper)
- Glass wool or small glass beads
- Beakers and conical flasks
- Pipettes
- Porcelain mortar and pestle
- Extraction flask
- Water bath
- Desiccator
- pH indicator paper
Reagents
- Concentrated hydrochloric acid (HCl)
- Anhydrous sodium sulfate
- n‑Hexane (extraction solvent)
Analysis Procedure
- Weigh 20 ± 0.5 g of wet sludge with a known dry‑weight fraction and place it in a 150 mL beaker.
- Acidify the sample to pH 2 using approximately 0.3 mL concentrated HCl.
- Add 25 g of magnesium sulfate hydrate (MgSO₄·xH₂O) and stir until a smooth paste is formed.
- Spread the paste along the sides of the beaker to aid evaporation. Allow it to stand for 15–30 minutes until solidified.
- Transfer the dried material to a porcelain mortar and grind into a fine powder.
- Place the powder into a paper extraction thimble.
- Wipe the beaker and mortar with solvent‑moistened filter paper and add the wipes to the thimble.
- Fill the thimble with glass wool or glass beads to ensure proper drainage.
- Mix 10 g of solid sample (with known dry‑weight fraction) thoroughly with 10 g anhydrous sodium sulfate and place into the extraction thimble.
- Perform solvent extraction at a rate of approximately 20 cycles per hour for 4 hours.
- Filter the extract using grease‑free cotton into a pre‑weighed boiling flask, wearing gloves to prevent contamination.
- Rinse the cotton and flask with fresh solvent.
- Attach the flask to a distillation setup and evaporate hexane by immersing the flask in a 70°C water bath. Collect solvent for reuse.
- When the distillation head reaches 50°C or the flask appears dry, remove the setup.
- Sweep the flask with air for 15 seconds using a vacuum source to remove solvent vapors.
- Wipe the flask exterior, cool it in a desiccator for 30 minutes, and weigh.
A solvent blank must be analyzed with each batch for quality control.
Calculation
Extractable Organics (%)
Where:
- W₁ = Initial weight of empty boiling flask
- W₂ = Final weight of flask after extraction
Results are reported as percentage of total dry solids.
Key Points for Accurate Results
- Ensure complete drying before weighing
- Avoid fingerprints or grease contamination
- Use high‑purity hexane
- Always run method blanks
- Maintain consistent extraction cycles and temperature
Final Thoughts
The analysis of extractable organics (oil & grease) in hazardous waste is a vital component of environmental monitoring and waste management. When performed carefully, this method provides reliable data for regulatory compliance, treatment design, and pollution control.
Understanding oil and grease behavior also complements other parameters such as BOD, COD, and TOC, offering a complete picture of organic pollution.
If you would like a detailed post on BOD analysis in wastewater or simplified infographics for this method, feel free to ask.
