A Colorado Plant Produces Sparkling Effluent With A Process Combining Liquor With Fixed-Film Media

A small but experienced team in Colorado produces sparkling effluent using an innovative process that combines mixed liquor with fixed-film media.
A Colorado Plant Produces Sparkling Effluent With A Process Combining Liquor With Fixed-Film Media
Salida operator Bryan MacNiven draws a sample for lab testing.

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Deep in the Rocky Mountains, Randy Sack and his three operators quietly treat wastewater and septage and discharge sparkling effluent to the Arkansas River.

Nothing seems to faze the team at the Salida (Colo.) Wastewater Treatment Facility. Together they have nearly 90 years of experience, all at the 2.7 mgd (design) Salida plant. Few seem to notice or appreciate what they do.

That’s why the 2013 Plant of the Year Award from the Colorado Rural Water Association was such a surprise. “We were unaware of it until we got a call from the association, asking if someone from our plant was going to be at the award dinner,” recalls Sack, plant manager. In fact, they hadn’t planned to attend and had never received any honors in the past.

“We really appreciate the award,” he says now. “It makes us proud that our hard work has been recognized. The crew really deserves this recognition.”

New processes

While the Salida crew has been around for a while, the treatment processes are relatively new — the plant was upgraded during 2010-2012. “We were having issues with ammonia and BOD,” Sack says. “We weren’t in violation, but it was real close.” The original plant was built in 1956; old trickling filters were replaced with rotating bio-contactors in 1985.

Salida hired the engineering firm of SGM of Glenwood Springs to perform a study and make treatment process recommendations. “We considered sidestream treatment, then decided to scrap everything and start new,” Sack says. “It came down to an oxidation ditch versus the IFAS [Integrated Fixed-Film Activated Sludge) process from Kruger.”

After reviewing processes at other plants, Salida chose the IFAS process, which adds polyethylene carrier elements to the aeration basins. The media provides a large surface area for beneficial microorganisms to attach, forming a biofilm that supplements the activity of the suspended microorganisms. As a result, the process provides enhanced treatment in the same volume of tankage.

The new plant takes flow from the City of Salida as well as wastewater from nearby Poncha Springs. Average daily flow at present is about 0.88 mgd. Influent flows by gravity over a bridge across the Arkansas River to the plant, where it enters the preliminary treatment facility for screening and grit removal (Vulcan screening washer). An air ionization odor control system from TransTech Energy and Environmental is positioned in the same area.

A pair of primary clarifiers (Evoqua) follow; the overflow is sent to two separate anoxic zones, and then to two aerated IFAS tanks, where the polyethylene media augments biological treatment, including nitrification. Turblex blowers (Evoqua) supply the air. The media is held in the activated sludge tank by retaining screens, while the mixed liquor flows on to two secondary clarifiers. A portion of the nitrified stream is recycled to the anoxic zone to achieve denitrification and partial BOD reduction upstream of the aerobic IFAS zones.

Clarifier overflow passes through a disc filter (WesTech Engineering) and then is disinfected in an Aqua Ray 40 HO UV system (Ozonia) before discharge to the Arkansas River, which flows eastward out of the Rockies.

Solids withdrawn from the system pass through a drum thickener and are pumped to an anaerobic digester. A centrifuge (Westfalia) dewaters the material. The resulting cake is composted on a drying pad and turned once or twice a day. Finished material is given away to the public after about a year of curing to a Class A quality.

Automated control

A SCADA system (Browns Hill Engineering & Controls) monitors and controls the entire treatment process. The project included a pump station designed for a 500-year flood that would enable the plant to force-feed wastewater out to the river in case of extremely high water.

The plant also features a large septage receiving area. “We receive septage from several counties — southern Park, Chaffee, Custer and Fremont, as well as ski resorts and the U.S. Forest Service station in southern Colorado,” says Sack. “The receiving area is completely computerized. Truckers put in their code numbers, then discharge their loads.”

Any shock ammonia loads are easily handled by the new IFAS system. The Salida plant has one more project on the list: “We want to put treated city water in here as our potable supply,” Sack says. “Right now, we’re on wells and they’re getting pretty old. The last one was drilled 15 years ago.”

The city water line will cross the Arkansas River to the plant and will ensure a continuous supply. While most of the plant is new, Salida was able to keep and use the existing anaerobic digesters, adding a new cover to the secondary digester. The preliminary treatment building was retained, although the screening system is more compact than its predecessor. The grit removal system is the same except for new pumps.

Staying ahead

If the old plant came close to permit limits on BOD and ammonia, that’s no longer a concern. After nearly two years of operating full-bore, the plant is averaging below 5 mg/L on BOD, considerably under the permitted level of 30 mg/L. Nitrogen is well below 1 mg/L.

Sack believes that if phosphorus removal requirements lie ahead, the plant will be able to meet them: “We’re testing for the state right now, trying to determine what we can do in terms of nitrogen and phosphorus.”

The upgrade was the largest capital project in the history of the city — about $18 million all told. The city creatively financed the project, prepurchasing some of the equipment and obtaining a $14.7 million loan from the U.S. Department of Agriculture, supplemented by a $1.4 million grant from the U.S. Department of Local Affairs.

Sack and his team have also been aggressive where lab work is concerned, performing their own analyses while also taking in samples from a number of small entities in the area, including ski areas, resorts and camps like the Young Life Ranch and Mount Princeton Hot Springs. “We can handle everything except bio-monitoring and metals, which we farm out,” Sack says.

In-house maintenance

The Salida team can handle just about everything where maintenance is concerned.

“We do 95 percent of our maintenance in-house,” says Sack. “We don’t do major electrical work, but we handle minor wiring especially on our pumps, and we have experience rebuilding all our pumps — including changing out packing to mechanical seals — and rebuilding our primary clarifiers.

“When we face an issue, we simply go out and make things right. We had a primary clarifier that got all bent out of shape. We drained the tank. Dan Poole started measuring and ordered the metal, and in two days a new clarifier scraper mechanism was welded, painted and installed. That’s the type of team I have.”

Then there’s the lawn. “If I had to describe our plant in a few words, I’d say ‘extremely clean,’” Sack says. “Sure it’s a wastewater facility, but our housekeeping is immaculate. Our lawn is mowed, the trees and shrubs trimmed. Nothing is overgrown. It’s a good way to keep sand and dirt from blowing around and dirtying up the place. When our council members come for a visit, they sometimes get mad because the landscaping here is nicer than anyplace else in town.” And who does the yard work? “We all do,” says Sack.

Sack, who was born and raised and played high school football in Salida, never thought wastewater treatment would be his profession when he started at the plant 36 years ago. “I was on the road a lot and needed something that would let me be at home,” he says.

The longevity of his career has rubbed off on the operators: 29 years for Bob Cannon, 19 years for Poole and four years for Bryan MacNiven. “I really appreciate the job these guys do,” says Sack. “You don’t often see this kind of longevity in this business. I think it shows you that we like what we do.”

More Information

Browns Hill Engineering & Controls - 720/344-7771 - www.brownshilleng.com

Evoqua Water Technologies, LLC - www.evoqua.com

GEA Westfalia Separator, Inc. - 201/767-3900 - http://us.westfalia.separator.com

Kruger USA - 919/677-8310 - www.krugerusa.com

Ozonia North America, LLC - 201/676-2525 - www.ozonia.com

TransTech Energy and Environmental - 412/904-4203 - www.trans-tech.org

Vulcan Industries, Inc. - 712/642-2755 - www.vulcanindustries.com

WesTech Engineering, Inc. - 801/265-1000 - www.westech-inc.com


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