2018 Excellence in Environmental Engineering and Science® Awards Competition Winner

Honor Award - Research

A Simple, Cost-Effective Method for NDMA Analysis in Drinking Water and Recycled Water to Improve Public Health Protection

Entrant: Orange County Water District
Engineer in Charge: Dr. Megan Plumlee, P.E.
Location: Fountain Valley, California
Media Contact: Dr. Megan Plumlee, P.E.

Entrant Profile

Orange County Water District (OCWD) is a groundwater management agency and recognized leader in water reuse, located in Fountain Valley, CA. OCWD was formed in 1933 and is responsible for managing, replenishing, and protecting the Orange County groundwater basin, which covers approximately 350 square miles in the lower watershed of the Santa Ana River and serves as the primary drinking water supply for over 2.4 million people. OCWD also operates the world's largest potable reuse facility, integrating advanced water treatment practices to achieve water quality that surpasses drinking water standards. This water is used to replenish (recharge) the groundwater aquifer.

For the submitted project, the Research and Development Department (R&D) of OCWD worked with researchers from Kagoshima University (Prof. Hitoshi Kodamatani) and Nagasaki University (Prof. Takahiro Fujioka) in Japan to validate their bench-scale prototype of a novel instrument for N-nitrosodimethylamine (NDMA) analysis. Funding for validation of the instrument was supported by The Water Research Foundation. Dr. Megan Plumlee, OCWD's Director of Research, was the Principal Investigator on the project, and the project was completed by OCWD Postdoctoral Research Associate, Dr. Shannon Roback. The prototype instrument was operated at OCWD and all samples were collected and analyzed by OCWD R&D staff. Additional water quality data to support the validation study was provided by the OCWD Advanced Water Quality Assurance Laboratory.

Project Description

N-nitrosodimethylamine (NDMA) is a disinfection byproduct formed in chloraminated drinking and recycled waters. NDMA precursors (secondary, tertiary or quaternary amines) react with chloramine to form NDMA, which is classified as a carcinogen by the United States Environmental Protection Agency at very low concentrations – just nanograms per liter (ng/L). As such, it is essential that potable water reuse and drinking water utilities minimize the amount of NDMA formed. While not yet regulated federally, NDMA has a drinking water notification level in California at 10 ng/L and is regulated in permitting guidelines for potable reuse projects in the state. Canada, Australia, Massachusetts and the World Health Organization also have published NDMA guidelines.

In spite of its health relevance and known occurrence in drinking/reuse waters, monitoring for NDMA is limited due to the expensive and time-consuming laboratory methods currently in use. These methods require costly instrumentation, the collection of large volumes of water and significant time from experienced laboratory staff. As a promising alternative, a new method for NDMA analysis has been developed. Orange County Water District (OCWD) scientists are collaborating with the method developers to rigorously test and validate the method using EPA methodologies. This method requires less time and labor, as well as a smaller initial investment in instrumentation while achieving the same detection limits. Significantly, the technology has been adapted to function as an online, near real-time monitoring instrument, which has great potential for operational and regulatory use at water treatment facilities like OCWD's.

Currently, online monitors for individual, trace-level, wastewater-derived organics ("trace organics") are not available, with the exception of monitors for trihalomethanes. Rather, online analysis at drinking and reuse facilities is limited to bulk organic indicators such as total organic carbon (TOC). As a particularly recalcitrant trace organic, NDMA may be a good indicator for poorly removed low molecular weight organics during reverse osmosis or other treatment steps. As such, use of an online NDMA monitor may be beneficial not only for monitoring the health-relevant and regulated compound itself, but also for ensuring process integrity for additional compounds of interest.

The rapid method was used to complete high-frequency monitoring of NDMA in the plant influent and effluent at OCWD's Advanced Water Purification Facility (AWPF), i.e., water recycling plant. Understanding the trends in NDMA occurrence better informs regulators as they develop monitoring guidelines and limits for permitting potable reuse plants. This effort required analysis of over 300 samples. Results indicated that NDMA concentration fluctuated significantly during a 24-hour period and during a seven-day week, demonstrating the importance of setting appropriate monitoring practices for regulatory approval, particularly in the context of direct reuse. Had these samples been sent to a commercial analytical laboratory for analysis, NDMA measurement would have cost approximately $150 per sample or $45,000 for all 300 samples. Such costs make high-frequency monitoring on a daily or weekly basis simply not sustainable for drinking water/reuse facilities.

At OCWD, the research and data collection benefits of the new method have already been realized, simply due to the ease of use (requires 2 mL of sample only, no extraction process) and low cost. This has allowed for the analysis of a large number of samples for projects that would otherwise be impossible. For example, an OCWD groundwater recharge basin was sampled at multiple locations every few hours for over 24 hours to determine the extent of photolysis of NDMA, which is the primary degradation mechanism, during recharge. The study, in one day, generated approximately 200 samples which were analyzed in just one week. This compares to typically 10 samples per week measured by the conventional method at OCWD's laboratory for plant monitoring purposes. In the recharge basin as well as in high concentration controls, NDMA was completely removed by natural (sunlight) photolysis. The study demonstrates the important role that environmental buffers – e.g., rivers, wetlands, ponds, groundwater aquifers – play in removing trace organics from water supplies, which must be considered now that more cities are designing and practicing direct potable reuse schemes (in which there is no environmental buffer).

Analytical chemistry often requires the use of toxic or harmful chemicals during laboratory procedures. Chemicals used in conventional NDMA analysis (extraction solvents, extraction resins and disposable extraction cartridges) may be harmful to the environment if not properly disposed of or mishandled. Plastics used in disposable extraction cartridges may persist in the environment for many years. Green chemistry efforts seek to eliminate organic solvents and laboratory waste. The new method validated at OCWD requires no extraction process, making it a greener alternative and protecting water, air and land resources.

The social and economic benefits of this method are derived from the fact that it makes monitoring for this carcinogen easier and much less costly, which will enable stronger protection of public health. A reduction in health care costs due a decreased burden of disease is borne out of the ability of utilities to better understand water quality and alter treatment to reduce concentrations of harmful contaminants. This public health protection is especially important for segments of the population living in disadvantaged communities without access to affordable and adequate healthcare. As a surrogate for other low molecular weight organics, which may also pose health risks, the reduction of NDMA in drinking/reuse waters will have social and economic benefits as the result of improved public health protection. Additionally, use of this method by potable reuse treatment plants, which may have higher NDMA occurrence due to NDMA precursors in source waters, will allow for better monitoring and corresponding treatment improvements. Improving the monitoring and engineering of these plants is particularly valuable for direct reuse facilities, which are increasing in the U.S. (in which the advanced treated water does not undergo environmental storage before use). Potable reuse water is typically less costly and more protective of the environment to produce than other water source alternatives in drought-prone regions (desalination, water importation).

Click images to enlarge in separate window.


OCWD operates the state-of-the-art Groundwater Replenishment System which uses advanced treatment to purify treated wastewater for potable reuse.	Liquid liquid extraction being performed at OCWD Advanced Water Quality Assurance Laboratory for conventional NDMA analysis. One liter of each sample must be extracted using harsh solvents in large glass flasks. This method is time and labor intensive and does not allow for a large number of samples to be run during each round of analysis.

The novel NDMA analytical method instrument (HPLC-PR-CL) consists of high-performance liquid chromatography (unit 1), use of an anion exchange module (controller is unit 2), a C18 reverse phase column and column oven (unit 3), the addition of luminol chemiluminscence reagent (unit 4), and a chemiluminescence detector (not shown).	Internal view of the HPLC-PR-CL instrument showing the C18 column (left), the anion exchange module which reduces background interferents (middle), and the photoreactor (right).

Typical chromatogram generated by the HPLC-PR-CL method showing NDMA followed by N-nitrosomorpholine (NMOR) at a 100 ng/L concentration.	This novel method requires only approximately 2 mL of sample (shown on left) compared to conventional NDMA methods which require at least 1 L of sample (shown on right) to determine NDMA concentration. This constrains study design due to the labor and cost of collecting and shipping large volumes of water.

OCWD postdoctoral research associate Dr. Shannon Roback and interns Alejandra Cano and Andrew Dinh collect samples at OCWD's Miraloma spreading basin to characterize NDMA photolysis by sunlight under natural conditions. Samples were taken at night to represent a control where no UV light was present.	In order to assess the accuracy, precision and detection limits of the HPLC-PR-CL method, various water matrices were spiked with known concentrations of NDMA and measured. The HPLC-PR-CL method met all U.S. Environmental Protection Agency criteria for analytical method validation. It also achieved a detection limit (1.5 ng/L) lower than most conventional methods (2 ng/L).

OCWD intern Jasper Kelly pipettes a water sample collected at OCWD's Advanced Water Purification Facility for storage and analysis by the HPLC-PR-CL method.	Samples analyzed as part of OCWD's characterization of diurnal fluctuations in NDMA concentration. Due to the small volumes needed to analyze samples, waste streams and the use of harmful chemicals and disposable products is minimized.