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Compact footprint & flexible hydraulics ease initial expansion and leave room for future growth
When Plainfield, Ind., needed to double its permitted capacity from 2 million gal per day (mgd) to 4 mgd at its South wastewater treatment plant, it faced a dilemma. Plainfield is on the southwest edge of Indianapolis and part of one of the fastest growing counties in Indiana, with growth projections extending well into the future. Like most treatment plants, space is at a premium there, and compact design was needed not only for the current expansion—including the addition of a post-aeration structure—but also to preserve as much room as possible for projected future expansions.
The existing UV system was space-intensive. It had a very narrow hydraulic operating range that required retaining an existing 30-ft-by-30-ft weir structure. Doing a replacement of this kind and adding a second unit for the additional capacity was going to consume critical space needed for the future.
Like most expansions of existing facilities, the hydraulic profile is set, and the new processes must fit within that profile. The selection of the post aeration structure was one critical decision. Whitaker Eng. selected an energy-efficient low-profile cascade aeration (LPCA) system designed to treat a range of flows from the current low instantaneous flow up to a peak instantaneous flow of 23.2 mgd. That being said, it was a challenge to fit the system into the existing hydraulic profile, expand the ultraviolet (UV) capacity and leave space for future expansion. Choosing the right UV system was key to making it all work, both today and for tomorrow.
The permit limits call for summer disinfection, April 1 through October 31, to meet E. coli limits of a monthly average (geometric mean) of no more than 125 colonies per 100 mL and a daily maximum limit of 235 colonies per 100 mL. To meet the diurnal peaks, the UV system needed to treat an instantaneous peak of 9.4 mgd.
Weatherproof stainless steel cabinets protect UV electrical systems and controls.
Whitaker Eng. chose a low profile, high-performance Wedeco Duron system. A major factor in the selection was the Duron system’s ability to function over a range of water elevations, up to 3.5 times the range of conventional UV systems. This flexibility allowed the water level for both the UV system and the LPCA to be controlled by a single combination weir gate, eliminating the need for the large weir structure of the existing UV unit. The LPCA could be located immediately downstream of the UV channel, again conserving space for the future.
The Duron system’s high power and energy-efficient Ecoray 600-W lamps can meet the peak disinfection requirement with only 36 lamps. Whitaker Eng. estimates that the low lamp count, combined with lamp cost and warranty life, will save Plainfield between $5,000 and $6,000 per year in lamp costs alone when compared with the other systems it evaluated. Combined with the 45-degree inclined banks, the low lamp count gives the Duron a very compact footprint, much smaller than those of the other systems evaluated.
In fact, the Duron system more than doubled the treatment capacity while occupying less channel space than the previous system. This compact footprint left enough space for future expansion, including up to three additional UV channels, for a total capacity of up to 42 mgd, as well as space for a future generator and sludge beds.
But ask Chief Operator Michael Gillespie what he likes best and he will say the many operational features that make the Duron easy to operate and maintain. The lamp sleeves of the previous system had to be hand-cleaned, a difficult task that was made even less pleasant—and potentially dangerous—by having to remove the UV system by hand, without even the assistance of a winch. Duron’s automatic wipers, activated by UV intensity sensors, keep the lamps operating at peak levels. There is never a need for hand-cleaning.
“The wiper system has worked really well,” Gillespie said. “It has really been foolproof.”
Autolift provides ease of access for safe, quick maintenance.
Changing lamps is also quick and easy. The sensors alert the operator when a lamp requires servicing and, at the push of a button, the automatic lift raises a bank from the water while the other banks continue treatment. The entire process is simple and safe. This same automatic lift speeds the annual winterization, lifting the banks out of the channel.
Duron combines energy-efficient lamps with real-time monitoring and control to save even more energy. Sensors monitor flow, UV transmittance of the wastewater and UV intensity. Controls adjust the lamp power up or down and turn banks off and on as needed to maintain optimal dosage delivery as conditions change. This real-time control prevents overdosing for lower energy expenditure while ensuring compliance. With the Duron system, Gillespie has never had to worry about compliance reporting.
“We typically have results of 40 and under, with a geometric mean of 10 or less,” he said.