Less than a half mile from the picturesque shore of Lavon Lake sits the Wylie Water Treatment Plant, operated by the North Texas Municipal Water District (NTMWD). The Wylie Plant provides drinking water to 1.6 million customers on a daily basis, a figure that is expected to double by 2050. The task of supplying billions of gallons of safe, great-tasting water per year to more than ninety communities across ten counties is a responsibility that the NTMWD takes very seriously.
The addition of chlorine and chloramines for drinking water disinfection has been a staple of water treatment for more than a century, but recent investigations into harmful compounds created by this process have cast doubt on the long-term sustainability of this approach. In 2006, the Environmental Protection Agency (EPA) issued new guidance for the control of harmful disinfection byproducts (DBPs) like trihalomethane (THM) and haloacetic acid (HAA), which in turn required that the district develop methods for reducing these contaminants.
Additionally, Lavon Lake experiences seasonal algae blooms. While these organisms do not present a threat to human health, they can impart an unpleasant, “earthy” taste to the water, leading to customer complaints. While drinking-water chlorination provides benefits, it is unable to remove the compounds that produce this taste and odor.
Facing new limits on acceptable levels of DBPs in the drinking water as well as age-old complaints about the taste during the algal bloom, the NTMWD turned to ozone disinfection as a possible alternative able to address both concerns. After carefully reviewing the alternatives, the NTMWD made a decision in 2008 to begin developing plans for an ozone treatment system, and in 2009 selected Metawater USA as the equipment supplier based on Metawater’s extensive experience with ozone treatment and its reputation for excellence and innovative design.
The plan called for the installation of 11 ozone generators, six at the north facility and five at the south facility, each capable of producing 3,900 pounds per day of 12% ozone gas, by weight. With a potential peak generation capacity of 42,900 pounds of ozone per day, the Wylie installation was at the time - and remains today - the largest ozone installation for drinking water in the world.
Ground was broken in early 2011, with the equipment delivered later that year. Construction and installation work continued for the next several years, with the northern generation facility substantially completed in May 2014, and the southern facility completed in October. By early 2015, the new ozone generators were providing disinfection and taste/odor reduction for up to 770 million gallons of water per day, at an annual operating cost of less than a nickel per thousand gallons.
The Aqua ElectrOzone™ system offers a number of advantages, including:
- Robust design with low breakage
- Reduced discharge gap that results in power savings
- Solid state pulse width modulation power
- Precision engineering for high dimensional accuracy
- Consistent ozone generation
- Extremely low failure rates
Since startup, the ozone generation systems have consistently met or achieved their treatment objectives, preventing the formation of DBPs within the guidelines of the Stage 2 DBP rule and below the stipulated Maximum Contaminant Level for these byproducts. The state-of-the-art control system has also provided greater flexibility to Wylie plant operators, allowing fine-tuning of ozone dosage in order to effectively respond to taste and odor events precipitated by the algae blooms. This important, cutting-edge upgrade will allow the NTMWD to provide safe, clean, great-tasting water to its millions of customers for many decades to come.
Aqua-Aerobic Systems is exhibiting at AWWA’s ACE17 expo in Booth 1401.
