Total Organic Carbon (TOC)

What is TOC?

Total Organic Carbon or TOC is a measurement of the amount of organic carbon present in water.

How is TOC measured?

The most common methods for Total Organic Carbon analysis are Method 415.1 (Combustion or Oxidation) and Method 415.2 (UV Promoted, Persulfate Oxidation). The test involves converting all organic carbon in a water sample to carbon dioxide (CO2) by utilizing heat and oxygen, chemical oxidants or UV radiation. The resultant CO2 concentration is measured with an infrared analyzer and reported as organic carbon (mg/L). The test takes 5-10 minutes to yield results in the lab, with continuous on-line analyzers also available.

Why is TOC Important?

In the drinking water industry, Total Organic Carbon is an important parameter that is often used as a general indication of water quality. Strict regulations are applied in many countries as elevated TOC levels have been directly associated with increased disinfection by-product (DBP) formation in the treatment process and bacterial regrowth in the distribution systems. In the United States, the Environmental Protection Agency (EPA) Stage 2 DBPR has set requirements for TOC removal based on source water characteristics.

TOC is also used in the industrial sector as a general water quality index and indicator of contamination.

Measuring TOC with UV-VIS Absorbance technology

Measurement of Total Organic Carbon with UV-VIS technology has many advantages over traditional methods. A number of organic compound in water strongly absorb UV radiation between 200-400 nm. Using absorbance data in this range and corresponding laboratory TOC data, excellent correlations can be made. For many applications, simply measuring absorbance at 254 nm and 550 nm will suffice for excellent correlations.

Comparable results to traditional TOC analyzers can be achieved without the use of expensive reagents. Additionally, the simplicity of the absorbance measurement principle reduces complexity and downtime, resulting in a better solution for real-time monitoring.

Where is TOC measured?

  • Influent to drinking water plant for source water quality fluctuations
  • Pre and post coagulation to optimize chemical dose for turbidity and organics removal
  • Pre and post carbon adsorption to monitor organics removal efficiency and optimize activated carbon dosing
  • Pre chlorination for DBP formation potential
  • Distribution system for general water quality and contamination events
  • Industrial wastewater process streams for product loss, specifically dairy
  • Industrial source water influent for ultrapure water production
  • Boiler systems for heat exchanger leaks and contamination