UKC 2005 – Water Treatment Session

Treatment of Emerging Contaminants (perchlorate, arsenic, MTBE, and NDMA) in Drinking Water

Joon H. Min, Carollo Engineers, Fountain Valley, CA, jmin@carollo.com, 714-593-5224

A number of drinking water utilities have been impacted recently by more stringent and new regulations, such as notification level, for emerging contaminants in water. These include most notably, perchlorate, arsenic, MTBE, TBA, and NDMA, that have been detected throughout the U.S. One of the challenges associated with treating these emerging contaminants is inefficiency of conventional treatment processes to deal with them. This paper will present results of several recent treatment studies and potential challenges associated with implementing treatment systems for these compounds.

Ion exchange (IX) process for perchlorate treatment have been successful in the past several years, but it produces perchlorate-laden waste that must be treated under certain cases. In California, biological processes have been conditionally accepted for drinking water application, but certain requirements are needed for effective implementation.

As utilities adopt adsorption process for arsenic treatment, the spent waste generated during treatment is also a concern where a utility may need to deal with transportation and disposal of the waste. pH and other competing anions affect treatment efficiency and thus the cost of treatment may increase substantially. Accumulation of other contaminants (e.g., uranium, etc.) could also limit disposal options of the adsorption media used for arsenic treatment.

For the case of MTBE, an advanced oxidation process (AOP) using UV is sometimes considered where the level of MTBE is high. During the oxidation of MTBE, TBA is generated as one of the oxidation by-products. TBA itself is an emerging contaminant, so the design of oxidation system should address such by-product formation issue.

Similar UV process can also be used to treat NDMA. Under certain conditions, however, re-formation after the UV treatment for NDMA or as by-product during ion exchange or conventional treatment where polymer is applied can occur. Other nitrosamine species may also pose challenges, as some states are considering to regulate them in addition to NDMA.

This paper will present the results of treatment studies for these contaminants and discuss the lessons learned in implementing treatment alternatives. These will provide a helpful guideline for utilities that are considering treatment of these emerging contaminants.