Determination of Mercury in Sewage Containing Hg-Loaded Particles

Significance of Mercury Determination in Sewage

Mercury is a highly toxic heavy metal that poses serious risks to aquatic ecosystems and human health when discharged in sewage. Accurate measurement of trace mercury levels is essential for regulatory compliance and process control in wastewater treatment. Determining mercury concentrations in sewage ensures that effluent meets environmental standards and helps to prevent bioaccumulation in the food chain.

Objectives and Study Overview

The primary goal of this application note is to demonstrate a reliable procedure for quantifying total mercury in sewage samples using the LECO AMA254 direct mercury analyzer. The study outlines sample preparation, calibration, analysis steps, and typical performance characteristics, with a focus on achieving a detection limit below 0.05 ppm and ensuring reproducibility in an industrial process control setting.

Methodology and Procedures

The analytical sequence consists of the following key steps:

• Sample Preparation: After homogenization, a 200 mg aliquot of sewage sludge is pipetted into a nickel boat without further pretreatment.
• Blank Determination: Three sequential blank runs purge residual mercury and validate system cleanliness.
• Calibration: Reference materials with known mercury content (e.g., LECO fly ash and NIST sludge) are weighed (200 mg) and analyzed across a dynamic range to establish a calibration curve based on peak area.
• Sample Analysis: Each sewage sample is weighed (~200 mg), identified in the software, and introduced into the nickel loop for automatic drying (140 s), decomposition (200 s), and detection.

Instrumentation

The analysis uses the following equipment:

• LECO AMA254 Direct Mercury Analyzer
• 614-822-114 Large Nickel Boats
• Precision balance (±0.1 mg)

Main Results and Discussion

Typical results for untreated sewage samples yielded a mean mercury concentration of 0.0620 ppm (SD 0.0024 ppm; RSD 3.89%). Following particle removal, mean values dropped to 0.0416 ppm (SD 0.0016 ppm; RSD 3.89%), demonstrating the method’s sensitivity around the 0.05 ppm threshold. The reproducible precision and low limit of detection confirm suitability for routine monitoring and process control.

Benefits and Practical Applications

This direct mercury analyzer method offers:

• Rapid analysis without chemical digestion.
• Low detection limits suitable for regulatory limits around 0.05 ppm.
• High precision (RSD <4%).
• Reduced sample handling and contamination risk.

Future Trends and Potential Applications

Emerging developments may include automated sample introduction, enhanced throughput via multi-sample carousels, integration with laboratory information management systems (LIMS), and expanded applications to other environmental matrices such as sediments and biota.

Conclusion

The LECO AMA254 provides a robust, accurate, and efficient solution for monitoring trace mercury in sewage. Its direct analysis capability, combined with precise calibration and minimal sample preparation, makes it well suited for industrial and regulatory laboratories focused on environmental compliance and public health protection.