The Issue at SNWA
Ozone is a really effective oxidant to meet disinfection or contaminant removal goals. Cryptosporidium is a parasite that has caused outbreaks in places such as Las Vegas and Milwaukee, and in the past, many ozone systems were installed at drinking water treatment plants to address that issue. Ozone is much more effective against Cryptosporidium compared to other disinfectants such as chlorine. Ozone is also effective at reducing the formation of other disinfection byproducts, particularly those that form during chlorination.
The problem is that ozone also reacts with bromide in water to form bromate. This is a really common problem in drinking water utilities that implement ozonation. Bromate is a regulated disinfection byproduct of ozonation, a chemical water treatment technique based on the infusion of ozone into water. Any utility that has bromide in their source water will likely have some concern about bromate production, which is regulated and needs to be monitored by the treatment plant to ensure it stays below its maximum contaminant level of 10 g/L. Typical ways to control bromate formation include maintaining low ozone exposures, at the expense of reduced disinfection efficacy, or using other chemical control strategies. Regardless of the approach, rapid bromate detection and quantification would ensure compliance with the regulation and efficacy of any bromate control strategy.
SNWA was looking for a solution that could rapidly detect how much bromate might be formed in its full scale ozone process. Standard methods are effective but require off-line analysis and are sometimes complicated by interfering constituents.
The Solution
SNWA became aware of the Metawater technology back in 2015 through an International Ozone Association (IOA) conference discussion Eric Wert, Project Manager for Applied Water Quality Research at SNWA, had about online bromate monitoring. The Metawater technology is an online analyzer, making it different than other offline methods traditionally being used. There are currently no online analyzers for bromate available on the market, which made Metawater, a Japan based company, a pretty innovative technology and approach that continued to gain the interest of SNWA. “So, we decided to bring it to WaterStart,” said Wert.
Metawater has had some success with its bromate analyzer at several treatment plants in Japan. Although it’s been successful in Japan, there were no tests performed in the US until this pilot with SNWA.
Utilities typically use offline methods with ion chromatography to monitor for bromate. The Metawater sensor uses a similar approach but in an online configuration and with fluorescence-based detection. If successful, a plant could monitor for bromate on an approximately hourly basis, which is the big benefit of this type of technology.
The Pilot
After SNWA pitched it to WaterStart, they opted to move forward with developing an agreement between SNWA, UNLV and Metawater to conduct testing of the technology’s ability to monitor bromate levels in treated water from Lake Mead. Metawater in return sent an older bromate sensor to UNLV for a controlled bench-scale evaluation and a newer prototype to SNWA for a two-year evaluation in an actual treatment setting. The overall goal of the project was to optimize the Metawater technology to improve its accuracy and precision in the challenging Colorado River water matrix. The technology’s prior success in Japan had primarily been on source waters with lower mineral and organic matter content.
One of the issues with bromate analysis in general, with offline and online technologies, is the presence of interfering constituents within the water. For example, some ions are present at orders of magnitude higher concentrations than bromate and can interfere with ion chromatography. Particularly with fluorescence-based detection, which is the case for the Metawater technology, bulk organic matter can also create a high background signal. This was the primary concern for the Metawater sensor, since it was determined to be less robust than standard offline methods at handling potential interference.
The idea of this pilot project was to determine how the operation of the sensor could be modified for challenging water matrices, possibly with pretreatment steps targeting interfering constituents. Potential solutions were identified, integrated into the sensors, and then tested to compare their performance and potential for full-scale implementation in southern Nevada.
Pilot Results
At the conclusion of the pilot, UNLV and SNWA concluded that the pretreatment strategies tested during the project showed promise but still required further optimization to ensure reliable operation in an actual drinking water application. The analyzer showed great promise as an online sensor for high purity applications, such as in the bottled water industry or even in drinking water systems with lower background interference. For example, systems relying on relatively pure snowmelt with an overall quality similar to the previously tested Japanese source waters (e.g., San Francisco and Reno) might be ideal settings for Metawater?s current technology. However, the existing and modified sensors were not sufficiently robust for monitoring bromate in Colorado River water in southern Nevada.
Further Development
SNWA had a final meeting with Metawater and explained that they would be open to collaboration in the future if different applications popped up, “because there are applications where the Metawater technology might be effective, such as with water sources that have less interference than the Colorado River,” said Daniel Gerrity, Associate Professor at UNLV and now Principal Research Laboratory Scientist at SNWA. Metawater has taken the sensor back to Japan and are working to improve the technology on their end based on some of UNLV and SNWA’s findings from the pilot.
This WaterStart project not only helped address the Metawater sensor, but according to Daniel Gerrity of SNWA, “it also led to other collaborations between Metawater, SNWA, UNLV, and other research partners. So, we were able to expand the original collaboration beyond the original bromate problem.”
About Metawater
Metawater is a prominent Japanese company that offers optimum solutions in water resource management through machine and electric engineering. Their efforts in the U.S. are currently being developed to prolong the life of or modify water treatment and recycling facilities. They aim to promote technological development that contributes to a safe, stable and reliable water environment.
