As Thornton, Colo., has grown over the past 50 years, it has accommodated this growth by following its motto of “City of Planned Progress.” The city’s latest preparation for future progress is the installation of UV water treatment systems from Aquionics. The closed chamber, medium pressure disinfection systems will allow the city to meet increased demands in water treatment capacity and tightening water quality regulations.
The city’s two water treatment plants, the Wes Brown Water Treatment Plant and the Thornton Water Treatment Plant, serve the needs of 114,000 citizens. With assistance from Aquionics representative Canyon Systems, Inc. (Lakewood, Colo.), Aquionics CrossFlow UV systems were chosen to provide a secondary barrier in the city’s water treatment process.
Three Aquionics systems work in conjunction with advanced ultrafiltration technology at the Wes Brown location, handling flow rates of 50 mgd. The quality of the source water (the South Platte River) is particularly challenging at this site, as effluent levels from upriver treatment plants can comprise up to 70% of the source water. At the Thornton site, where the quality of source water from Clear Creek is less of an issue, conventional filtration is combined with two Aquionics systems to handle 20 mgd.
The UV systems eliminate pathogens and reduce disinfection byproducts (DBPs), meeting water quality regulations governed by the U.S. EPA. At both plants, chlorine is applied after UV treatment for residual maintenance in the distribution system. With the installation of UV, the amount of residual chlorine needed has been reduced, resulting in a corresponding reduction in DBPs such as Trihalomethanes and Haloacetic Acids.
The compact design and high efficiency of the systems were major selling points for the city of Thornton. “Capital cost was not our only consideration – we also took into account projected construction, operating and maintenance expenses over time,” explained Bud Hart, city of Thornton manager of water supply treatment and quality. “The footprint of the Aquionics units allowed us to retrofit our existing facilities, while the low power consumption will keep our operating costs down.”
Maintenance on the system is also low; periodic replacement of the UV lamps can be carried out easily by onsite staff. An automatic cleaning mechanism keeps lamp sleeves free of organic deposits for consistent UV dosing. Each chamber is also fitted with UV monitors to measure actual UV fluence and dose for record keeping. With the addition of an optional online transmittance monitor, real time transmittance values are used to automatically adjust the dose pacing of the UV system.