Using TOC Analysis for Disinfection Byproduct (DBP) Control

The US Environmental Protection Agency recently introduced new regulations to help further reduce health risks associated with Disinfection Byproducts (DBPs).

by Erin Milkis

The US Environmental Protection Agency recently introduced new regulations to help further reduce health risks associated with Disinfection Byproducts (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.

GE Analytical Instruments’ Sievers 5310 C Laboratory TOC Analyzer or the new 5310 C On-Line TOC Analyzer can both be used to monitor a municipal plant’s influent, effluent, or any other plant location TOC level. The instruments will be on display during ACE ‘08 at the GE booth.

How TOC Relates to DBPs

Several DBPs have been linked to cancer in laboratory animals and are therefore regulated. Naturally occurring carbon compounds are not hazardous by themselves, but combined with a disinfectant they produce byproducts, which pose a health concern. THMs, one class of DBPs, are formed from the interaction of TOC, naturally occurring bromide, and chlorine.

Some plants not only monitor TOC but have also started TOC profiling their entire treatment plant. This is accomplished by testing TOC values at all points in a plant and each treatment train, determining where the majority of TOC reduction does or does not occur in order to impact DBP levels. Changes can then be implemented to improve TOC reduction.

For example, if a Sievers 5310 C On-Line TOC analyzer is installed to measure the plant’s effluent continuously and TOC values spike unexpectedly, other samples can be run from the source water and other plant locations to see where the TOC increase occurs. Grab samples can be run at any time on the same on-line TOC instrument, allowing for a quick check of other TOC locations, such as prior to coagulation, after coagulation, or after filtration, with no need to disconnect the on-line water source.

The 5310 C TOC analyzers were developed specifically for drinking water applications. The instruments have an analytical range of 30 parts-per-trillion to 50 parts-per-million and use SM 5310 C for USEPA compliance monitoring of raw and finished drinking water.

The instruments offer automated calibration and verification procedures, 4-minute analysis time, and automated reagent adjustment. Additional productivity enhancements are realized with the optional 900 Autosampler, featuring random access capability and up to 120 sample positions.

Engineered for simplified operation, the analyzers needs no external reagents or gas supplies and require only two hours of preventive maintenance per year. Twelve-month calibration stability frees analysts to perform other critical tasks. A large, color touch-screen display provides an intuitive menu for easy setup of instrument parameters.

DBP Regulation Overview

The Stage 1 Disinfectants and Disinfection By-products Rule (D/DBPR), promulgated in December 1998, was the first phase of the 1996 Amendments to the Safe Drinking Water Act. Stage 1 D/DBPR not only set limits at surface water and groundwater plants for the DBPs, such as THMs and haloacetic acids (HAA5) , but also established a TOC percentage removal requirement for utilities utilizing conventional treatment processes (see Table 2). Many surface water plants utilize conventional filtration, using coagulants to remove TOC, also termed “DBP precursors,”1 because of their interaction with a plant’s disinfectant.

The EPA uses the term enhanced coagulation to define the process of obtaining improved removal of TOC by conventional treatment in order to limit DBP formation. The Stage 2 D/DBPR, published on January 4, 2006, is meant to further reduce the potential health risks from DBPs beyond the Stage 1 regulation. The Stage 2 D/DBPR does not replace the Stage 1 DBPR; instead it is an extension of the original rule. Systems must comply with all Stage 1 requirements, such as not exceeding maximum contaminant levels (MCL) for chlorite and bromate (Table 1), and TOC removal requirements (Table 2), as well as the Stage 2 regulations.

Stage 2 D/DBPR changes the way DBP sampling results are averaged for compliance. The Stage 2 D/DBPR regulation is based on a locational running annual average (LRAA) which means compliance must be met at each monitoring location, instead of the system-wide running annual average (RAA) used under the Stage 1 DBPR. Plans for monitoring were due as early as 2006 for the largest municipalities. Compliance monitoring for Stage 2 begins in 2012 for the largest systems. By October 2013, all systems, regardless of size, must be in compliance. The frequency of monitoring for DBPs will be quarterly for most systems. The requirements behind the Stage 2 D/DBPR forces a utility that has struggled in the past to meet the DBP requirements from Stage 1, to take even more steps to control DBPs. TOC analysis is one way to better understand a plant’s DBP levels and the changes that can be implemented to control TOC and therefore DBPs.

Conclusion

As the EPA continues updating the Safe Drinking Water Act to limit health risks surrounding DBPs, drinking water utilities remain challenged to meet the corresponding regulations. To maintain DBP levels below the acceptable limit, a water treatment plant must fully understand the characteristics of the DBP precursors in their source and distribution water. A large part of maintaining compliance with the D/DBPR rule involves monitoring organic levels and understanding how a treatment process impacts TOC. Using GE Analytical Instruments’ Sievers 5310 C TOC Analyzer to know where TOC is or is not being removed within a plant will help a utility make the appropriate process changes to prevent today’s TOC from becoming tomorrow’s THMs.

About the Author: Erin Milks is a Municipal Applications Specialist for GE Analytical Instruments.

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