Modern Hexane-Extractable Material (Oil & Grease) Analysis in Wastewater Samples

Importance of the Topic

The measurement of n-hexane extractable material (oil & grease) is an operationally defined method widely employed to monitor hydrocarbon pollution in wastewater including aromatics, aliphatic hydrocarbons, fatty acids and oils. This parameter plays a critical role in regulatory compliance, treatment plant performance assessment and prevention of sewer blockages.

Objectives and Overview

This study evaluates the automation of US EPA Method 1664B using solid phase extraction (SPE) on the SPE-DEX 3100 system. Key goals include verification of method detection limit (MDL), precision and recovery for both 47 mm and 100 mm SPE disks, and demonstration of performance in real wastewater samples.

Methodology

An automated SPE protocol was implemented as follows:

• Sample preparation: 1 L of reagent water or wastewater acidified to pH < 2 and spiked with hexadecane and stearic acid standards.
• Extraction: SPE-DEX 3100 Oil & Grease Extraction System with 47 mm or 100 mm Pacific Premium SPE disks.
• Cleanup: In-line WaterTrap™ drying; silica gel treatment for nonpolar fraction (SGT-HEM).
• Evaporation and Gravimetric Analysis: Speed-Vap IV at 40 °C and Mettler AE 200 balance for mass determination.
• Quality Control: Initial precision and recovery (IPR) with four replicates; MDL determination with seven spikes and one blank.

Instrumentation

• SPE-DEX 3100 Oil & Grease Extraction System (Horizon Technology).
• Speed-Vap IV Evaporation System with 105 mm aluminum pans.
• Mettler AE 200 analytical balance.
• Pacific Premium SPE disks; silica gel and glass wool for SGT treatment.

Main Results and Discussion

MDL values of 0.68 mg/L (47 mm disks) and 0.89 mg/L (100 mm disks) were achieved, surpassing the 1.4 mg/L target. IPR data yielded HEM recoveries averaging 97.3 % (SD ≤ 2.0 %) and SGT-HEM recoveries of 88.8–91.1 % (SD ≤ 2.5 %), meeting acceptance criteria. Wastewater spike recoveries ranged from 80.3 to 88.8 %, demonstrating robustness in complex matrices. Automated SPE eliminated emulsion formation, reduced solvent use and improved reproducibility.

Benefits and Practical Applications

• Full compliance with US EPA Method 1664B regulatory limits.
• Reduced solvent consumption and operator exposure through automation.
• Enhanced throughput suited for both small-scale and high-volume laboratories.
• Reliable handling of particulate-laden samples without manual intervention.

Future Trends and Potential Applications

Further integration with spectroscopic or mass spectrometric detectors could enable compound-specific monitoring. Development of greener solvent systems and miniaturized SPE formats may increase sustainability and portability. The approach can be extended to emerging contaminants and real-time wastewater surveillance.

Conclusion

Automated SPE using the SPE-DEX 3100 system fulfills stringent performance criteria of US EPA Method 1664B, offering a reproducible, high-throughput and solvent-efficient solution for oil and grease analysis in wastewater.

Reference

1. Yang M., Produced Water, Springer 2011.
2. Stenstrom M.K., Fam S., Silverman G., Environmental Technology Letters, 7, 625–636 (1986).
3. US EPA Method 1664B: n-Hexane Extractable Material (HEM) by Gravimetry, 2010.
4. ISO 11349: Water Quality – Gravimetric Method, 2010.
5. Standard Methods 5520G, 21st Edition.