The Alabama city of Auburn in 2012 converted the disinfection system at its H.C. Morgan Water Pollution Control Facility from chlorine to UV.
Since the UV system went online in October of that year, it has consistently outperformed the plant’s regulatory requirements for E. coli of 126 cfu/100 mL monthly average May to November and 548 cfu/100 mL monthly average December to April. The conversion made use of the existing chlorine contact tanks and fixed weir to reduce construction cost, while also enabling surplus space in those tanks to be repurposed.

Variable Loads

Auburn, home to Auburn University, faces treatment challenges common to college and university towns. The population of 56,900 swells significantly on fall weekends when crowds descend for Auburn Tigers football games.

Located between Montgomery, Ala., and Atlanta, Ga., along Interstate 85, Auburn has seen rapid growth in recent years. Separate wastewater treatment plants were built to serve the city’s two sewer service basins: the 2 mgd (permitted capacity) Northside Water Pollution Control Facility, and the 11.25 mgd H.C. Morgan plant.

Both were built in 1985 and were the first privatized plants in the state. The city owns the facilities and has a contract with Veolia Water North America to operate and maintain them. In 2008, the U.S. EPA and Alabama Department of Environmental Management imposed a total maximum daily load limit on total phosphorus for the Saughatchee Creek Watershed, which received the Northside plant’s effluent.

After reviewing compliance options with consultants from CH2M HILL, the city decided to cease treatment and discharge at the Northside plant and use a recently built transfer sewer to pump that plant’s influent to the H.C. Morgan plant, which would be upgraded to handle the additional flow. The Northside plant now in effect serves as a lift station.

Due Diligence

The H.C. Morgan activated sludge/extended aeration plant on 40 urban acres discharges to Parkerson Mill Creek. As part of the upgrade in 2012, the city decided to convert to UV for its safety advantages and for long-term operation and maintenance cost savings.

The city had been disinfecting with gaseous chlorine and dechlorinating with sulfur dioxide. “Like a lot of plants, this one was built in the middle of nowhere, but now we have a subdivision, apartment complexes and a golf course around us,” says Matt Dunn, P.E., assistant director of the city’s Water Resource Management Department.

“We’ve never had a problem with chlorine, but it only takes one leak to lead to a potentially dangerous situation. With those developments close to our plant, continuing disinfection with chlorine became a bigger safety concern.”

The safety of plant personnel was also a concern, notes Scott Milner, project manager with Veolia Water: “Chlorine gas is a great disinfectant, but we think it’s better to get away from using a chemical if you can.”

With CH2M HILL, the city evaluated UV technologies, in the process making site visits to see systems in action. They selected the TrojanUVSigna system from TrojanUV for its suitability for seasonal operation, low number of UV lamps, ease of operation and maintenance, low installed cost and low long-term operating cost.

“We looked at UV in the past,” says Dunn. “It’s a case where as more vendors offer a technology and refine it, costs start to go down. So adopting UV became more financially attractive than it was several years ago.”

Online Performance

The retrofit installation into the existing chlorine contact basin proceeded quickly and without incident. Free space in the old tanks is used for water storage, bypass and other purposes. The installation came online just in time for the 2012 college football season. It includes two 22-lamp banks (expandable to 29) to treat a peak hourly capacity of 34.2 mgd. The plant has excellent effluent quality with UV transmittance that consistently exceeds 65 percent.

The TrojanUVSigna system is designed for large-scale wastewater disinfection, for ease of conversion and for low ownership cost compared to chlorine. It uses TrojanUV Solo Lamp technology, designed to combine the advantages of medium-pressure lamps (low lamp count, small footprint, dimmable from 100 percent to 30 percent power) and low-pressure high-output lamps (one-third the energy usage of medium-pressure lamps, more than 15,000 hours lamp life, and low carbon footprint and environmental impact).

Dunn and Milner appreciate the angled lamp arrangement, which allows lamps to be replaced without disrupting disinfection by removing the lamp banks from the channel. Individual lamps can be turned off at the local control panel.

“You can basically walk out on the system, give an interlock mechanism a quarter-turn and slide the lamp right out of the sleeve,” says Milner. “There is also a hydraulic system that pivots the banks out of the channel. Banks of UV lamps do not need to be removed for routine maintenance such as lamp replacement or sleeve cleaning. The push-button pivot feature can be used when operators want to inspect the banks and for cleaning the bank or channel as required.”

The system incorporates advanced control and the company’s maintenance-saving ActiClean automatic chemical/mechanical cleaning system, which eliminates fouling on lamp sleeves and is third-party validated to maintain at least 95 percent of sleeve UV transmittance. The same hydraulic system drives both the lamp sleeve cleaning and the pivot function.

Positive Results

“Through our first year of operation, we found the system really simple to operate and maintain,” Milner says. “TrojanUV has been a pleasure to work with. The support and service have been excellent, and we look forward to working with them in the future.”

Dunn concludes, “The bottom line is making sure we consistently meet our permit limits for E. coli, and we’ve had no issues with that. We are consistently below our limits even during high-flow situations. It’s a nice system, and we’re pleased to have it at our plant.”