Determination of adsorbable organic halogen in wastewater using a combustion ion chromatography system

Significance of the Topic

Organohalogen compounds pose significant environmental risks due to their toxicity and persistence. Monitoring adsorbable organic halogens (AOX) provides an aggregate measure of halogenated organics in wastewater and is critical for regulatory compliance and pollution control.

Objectives and Study Overview

This study aimed to integrate an automated combustion unit with ion chromatography (IC) to quantify AOX in wastewater. The developed method aligns with EPA Clean Water Act, EPA RCRA and Chinese environmental standards, offering halogen speciation (fluoride, chloride, bromide) and improved analytical throughput.

Methodology and Instrumentation

• Sample Preparation and Adsorption: Wastewater samples are acidified and passed through granular activated carbon (GAC) columns to adsorb organic halides, followed by nitrate wash to remove inorganic halides.
• Combustion Ion Chromatography System: A Mitsubishi AQF-2100H Auto Quick Furnace and COSA GA-210 gas adsorption unit are interfaced with a Thermo Scientific Dionex Integrion HPIC. Samples are combusted at 900–1000 °C, converted to halide ions, absorbed in water, and analyzed.
• Chromatographic Conditions: Separation on Dionex IonPac AG18-4µm guard and AS18-4µm analytical columns with electrolytically generated 30 mM KOH eluent, suppressed conductivity detection, 1 mL/min flow, 100 µL injection, and 10 min run time.
• Calibration and Standards: Fluoride, chloride, and bromide standards were prepared at seven levels (0.1–5, 0.2–10, 0.4–20 mg/L). Linear calibration was achieved for chloride and bromide (r2>0.99997), and quadratic for fluoride (r2=0.99998).

Main Results and Discussion

• Separation Performance: Baseline resolution of F–, Cl–, and Br– within 10 min enabled efficient analysis.
• Linearity and Precision: Chloride and bromide showed linear responses; fluoride fit a quadratic model. Peak area and retention time RSDs were <1% and <0.2%, respectively.
• Recovery and Accuracy: Spiked DI water recoveries ranged 87–114% with RSDs <5.1%. Wastewater samples spiked with AOX showed recoveries of 95–105% across three sites, demonstrating reliability in complex matrices.

Benefits and Practical Applications

• Fully Automated Workflow: Reduces manual handling, minimizes errors, and increases throughput.
• Speciation Capability: Provides individual halide quantification versus sum titration methods.
• High Precision and Sensitivity: Suitable for regulatory monitoring and industrial QA/QC.

Future Trends and Possibilities

Developments may include integration with laboratory information management systems for real-time reporting, miniaturized combustion reactors for reduced sample and reagent consumption, and expansion to other halogenated pollutants. Advances in detector sensitivity and faster chromatography will further enhance throughput and detection limits.

Conclusion

The combined combustion IC approach delivers accurate, reproducible determination of adsorbable organic halogens in wastewater. Automation and speciation capabilities satisfy stringent environmental regulations and support robust industrial monitoring.

Reference

1. Working Draft DIN 38409-59, F. Schmitz, LHL Wiesbaden, Germany.
2. Thermo Scientific Application Note 1145, 2016.
3. Thermo Scientific Application Note 72268, 2017.
4. NEPS of China HJ/T83-2001.
5. EPA Method 1650 Revision C, 1997.
6. EPA Method 9020B Revision 2, 1994.
7. Thermo Scientific Technical Note 175, 2016.
8. Thermo Scientific Technical Note 72211, 2017.
9. Mitsubishi AQF-2100H Operation Manual.