Continuous Monitoring of Treated Drinking Waterfor Trihalomethane (THM) Disinfection By-productsUsing a CMS5000 Monitoring System

Importance of the Topic

The formation of trihalomethanes (THMs) during water disinfection poses a health risk and is regulated by USEPA, which limits total THM concentration to 80 ppb in finished water. Continuous monitoring is essential for ensuring treated water compliance and protecting public health.

Study Objectives and Overview

This application note details the development of an automated method using the INFICON CMS5000 Monitoring System for frequent on-site measurement of total THMs (TTHMs) in treated drinking water. The study aims to demonstrate the system’s capability for continuous sampling, analysis, and reporting without manual intervention.

Methodology

Calibration standards at 1, 5, and 10 ppb were prepared by spiking VOC-free water with a THM mixture. Samples were purged with argon into a purge-and-trap headspace, captured on a carbon concentrator for one minute, then analyzed by gas chromatography with an 8-minute temperature-programmed method (60 °C to 180 °C). Quantitation was based on a three-point quadratic calibration curve. Verification was performed using an independent 5 ppb THM standard to assess method accuracy.

Used Instrumentation

• CMS5000 Monitoring System combining a purge-and-trap sampler and gas chromatograph
• GC column: HP-1MS, 15 m length, 0.32 mm ID, 4.0 μm film thickness
• Purge-and-trap headspace concentrator with argon gas

Main Results and Discussion

• Verification recoveries for individual THMs were 112% (chloroform), 110% (bromodichloromethane), 94% (dibromochloromethane), and 86% (bromoform)
• Total THM recovery was 105% for a 20 ppb TTHM standard
• The CMS5000 system provided reliable quantitation within regulatory limits and enabled multiple daily measurements without operator involvement

Benefits and Practical Applications

Continuous, automated monitoring allows treatment plant operators to detect fluctuations in organic load and ensure compliance with EPA standards. The system reduces labor, minimizes response time to THM spikes, and enhances overall water quality management.

Future Trends and Applications

Advances may include integration with remote data networks and IoT platforms for real-time alerts, expansion to monitor additional disinfection by-products, and development of faster or more sensitive detectors to address emerging contaminants.

Conclusion

The INFICON CMS5000 Monitoring System offers an effective solution for on-site continuous measurement of THMs in treated drinking water, ensuring consistent compliance with regulatory limits and supporting public health protection.

References

• INFICON Application Note: Continuous Monitoring of Treated Drinking Water for Trihalomethane Disinfection By-products Using a CMS5000 Monitoring System, 2009