Breaking Down Disinfection Byproducts
Understanding key regulatory changes that lie ahead
As research continues to shed light on disinfection byproducts (DBPs), regulatory limits are tightening. Here Leo P. Zappa, director, municipal water market, for Calgon Carbon Corp., discusses how to achieve compliance.
Neda Simeonova: What are some of the most popular municipal disinfection methods in the U.S. and other developed countries?
Leo P. Zappa: The primary means of disinfection in the U.S. remains the injection of chlorine. Other methods that have gained traction in more recent years include injection of alternative disinfectant chemicals such as chloramines (chlorine plus ammonia) and chlorine dioxide, and the use of ozone and ultraviolet light systems. It is the same for most other developed countries.
Simeonova: What new DPB developments are you seeing, and why should they be a cause for concern?
Zappa: Recent research has increased our awareness that the use of alternative disinfectants can lead to the formation of emerging DBPs, and that some of these emerging DBPs are more toxic than those currently regulated. This points to the fact that changing disinfectant chemicals is not an effective means of reducing exposure to DBPs.
Simeonova: How does the impending U.S. EPA Stage 2 DPB Rule differ from Stage 1 in compliance?
Zappa: The difference between Stage 1 and Stage 2 is how data regarding DBP levels are reported. In Stage 1, DBP levels (both total trihalomethanes and the five regulated haloacetic acids) measured in a utility’s water distribution system were collected from each monitoring location on a quarterly basis, and reported on a running annual average basis for the entire distribution system. This reporting system had the effect of diluting the impact of one or two “hot spots” of high DBP concentrations by averaging those results in with the data from the other monitoring locations, and Stage 1 only required that the entire distribution system, on average, be in compliance. Stage 2 has changed the reporting system to a locational running annual average, which means each monitoring station is sampled and reported separately.
Simeonova: What are currently the best ways to meet the requirements of the Stage 2 DBP rule?
Zappa: There are two approaches to meeting the Stage 2 requirements. The first, and in my opinion, best approach is to remove the organic precursors present in the water. By removing these precursors, the DBP formation potential of the water is reduced, thus reducing DBP levels throughout the distribution system. This approach also allows the utility to use whatever chemical disinfectant it chooses, as none will form appreciable levels of DBPs once the organic matter is removed from the water.
The other way to comply with Stage 2 is to switch from chlorine to an alternative disinfectant, such as chloramines. The current regulation is based on the control of DBPs formed primarily by chlorine. As mentioned previously, the downside to this approach is that most of these alternative disinfectants, while forming lower levels of the currently regulated DBPs, often form higher levels of other, emerging DBPs.
Simeonova: Why is adoption of GAC effective for DBP regulatory compliance and beyond?
Zappa: Granular activated carbon (GAC), is one of the most cost-effective means of removing organic precursors from water. GAC removes the natural organic matter through adsorption, in which the organic compounds are trapped within the structure of the carbon granule. GAC has a great capacity for organic compounds and can be employed far more cost-effectively than other precursor removal technologies such as membrane filtration systems.
As new emerging DBPs are discovered, the emphasis in controlling the presence of such compounds in drinking water will shift away from switching to alternate disinfectants and toward organic precursor removal. As a result, I would expect that more and more water utilities will look to employ technologies like GAC to accomplish this task.