Today’s TOC; Tomorrow’s THMs - How Total Organic Carbon (TOC) Analysis Relates to Disinfection Byproducts such as Trihalomethanes (THMs) and the Corresponding EPA Regulations

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Courtesy of GE Analytical Instruments

Introduction

The US Environmental Protection Agency (EPA) amended the Safe Drinking Water Act (SDWA) in 1996 to balance the risks presented by microbial pathogens and by-products from the disinfectant used to destroy these microbes. The byproducts, called Disinfection Byproducts (DBPs), form from the interaction of the naturally occurring organic matter (NOM) in a treatment plant’s source water and its disinfection process. NOM is typically measured as total organic carbon (TOC). DBPs, such as trihalomethanes (THMs), continue to form as water passes through a plant’s distribution system and contact time increases. Therefore, it is said that the TOC measured in a plant today can be measured as DBPs tomorrow.

The EPA recently introduced new regulations to help further reduce health risks associated with DBPs. These changes will make meeting the DBP rules more difficult, and in turn make understanding a plant’s TOC values and the correlation to DBP levels even more critical.

How TOC Relates to DBPs

TOC in drinking water is formed from the decay of naturally occurring vegetation, including algae, sediment, and particles in water. TOC content in water sources varies from region to region, by type of water body, and even seasonally within a water source. Algae blooms, for example, are usually more prominent in summer and early fall, and can increase the organics of a source water. TOC can also be increased in a raw water source through the transfer of other water sources, nearby wetlands, terrestrial runoff, or river channels. There are also quite a few man-made organic chemicals such as industrial solvents, hydrocarbons, pesticides, and herbicides derived from industrial sources and contributing to TOC.

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