Total Organic Carbon (TOC)

 

 

Introduction

Water; we drink it. Its an ingredient in commercially manufactured food, beverages and pharmaceuticals. In industry, we use it to generate electricity, to heat, to cool, and to rinse. Nearly all manufacturing processes require water at some point, and all this water is, eventually, returned to the environment.

As our population grows, and as industries refine their processes, water quality is increasingly important. Organic contaminants in water represent a unique threat to public health.

In industry, organics threaten profitability through reduced product quality or through fines associated with discharge permit violations.
In the environment, discharged organics enter the ecosystem, where they compete for food and oxygen, or become nutrients. Excess nutrients can create an imbalance in surface water that results in algae blooms.

Detecting and quantifying concentrations of organics in water helps to protect human populations, industrial processes, and our environment.

 

 

Total Organic Carbon (TOC)

Total Organic Carbon (TOC) is a sum measure of the concentration of all organic carbon atoms covalently bonded in the organic molecules of a given sample of water. TOC is typically measured in Parts Per Million (ppm or mg/L), although some industries require more refined measurements expressed in parts per Parts Per Billion (ppb or µg/L), or even Parts Per Trillion (ppt).

As a sum measurement, Total Organic Carbon does not identify specific organic contaminants. It will, however, detect the presence of all carbon-bearing molecules, thus identifying the presence of any organic contaminants, regardless of molecular make-up.

A typical analysis for TOC measures both the Total Carbon (TC) as well as Inorganic Carbon (IC, or carbonate). Subtracting the Inorganic Carbon from the Total Carbon yields TOC. (TC-IC=TOC). Another common variant of TOC analysis involves removing the inorganic carbon by purging the acidified sample with carbon-free air prior to measurement, then measuring the remaining carbon. This measurement is more accurately called non-purgeable organic carbon (NPOC).

 

 

Who Measures TOC?

Total Organic Carbon is a broadly useful measurement. TOC is a required measurement in municipal water and wastewater systems, and is also a valuable measurement in a host of industries that rely on TOC analysis for process control and for reporting of regulated organic discharge levels. Industry often turns to TOC analysis to protect vital systems by monitoring raw water feedstock and process water quality.

IN MUNICIPAL DRINKING WATER:

As a regulated monitoring parameter in municipal and environmental water programs, TOC measurement provides a method of detecting organic contaminants that can pose a threat to public health.

 

IN MUNICIPAL WASTEWATER:

Early detection of high organic loads in influent enable plant operators to optimize processing for improved system efficiency. Analyzing TOC levels in effluent demonstrates compliant levels of organics prior to discharging treated wastewater to surface waters.

 

IN INDUSTRIAL WASTEWATER:

Industrial discharge is carefully regulated, and excessive organics in industrial wastewater can result in fines, citations and, in extreme cases, even plant closure. Individual states enforce national US EPA regulations by requiring that industries hold discharge permits in order to operate. National Pollutant Discharge Elimination System (NPDES) permits stipulate each permit holder's unique limits and monitoring requirements for discharge of contaminants.

 

IN PROCESS INDUSTRIES:

In process industries TOC analysis provides cleaning validation and detects organic contaminants in process water. The presence of organic material in pure water systems can indicate a failure in filtration systems, storage methods, compromised seals or other system component failure. Monitoring total organic carbon is vital in many industries, including Power Generation, Production of Pharmaceuticals, Semiconductor Manufacturing, and any industry where ultrapure water (De-Ionized, or DI Water) is produced or consumed.

 

 

 

How Is TOC Measured?

TOC measurement is achieved by oxidizing a sample of water, thus converting the organic constituents to carbon dioxide (CO2). Oxidation is achieved through combustion, or with a UV/persulfate reactor. If Inorganic carbon can be stripped out through acidification and the resulting CO2 is then measured with a nondispersive infrared detector. Organic molecules can be oxidized using heat, oxygen, ultraviolet irradiation, chemical oxidants, or combinations of these.

 

 

Why Monitor TOC?

Organic carbon readily binds with other elements in the environment, producing any of a large number of compounds, many of which are harmful to the environment or threaten the public health. US EPA regulations require that industries limit their environmental discharge of organic carbon, and violations are often accompanied by severe financial penalties. In severe cases, losing an NPDES permit can lead to plant closure.

Many industries monitor TOC as a means of validating sanitary conditions. This is especially critical in industries that use high purity water as an ingredient in pharmaceutical products (water for injection), and as a rinsing or cooling agent to protect expensive industrial systems.