When the city of El Dorado, Kan., needed to upgrade its trickling filter/rotating biological contactor plant to meet ammonia limits and deal with high rain events and more stringent nutrient removal specifications, plant managers devised a unique solution.

Started up in February 2007, a new 3 mgd (design) wetlands/activated sludge plant produces exceptionally high-quality effluent and Class A biosolids. The biosolids are applied to neighboring city-owned farmland, and a share of the value of the farmer’s yield is returned to the treatment plant.

The El Dorado Wetlands and Water Reclamation Facility has produced effluent far better than permit limits, and the agreement with the farmer nets the city $40,000 to $50,000 per year. A recipient of multiple awards, the El Dorado facility has accomplished all this with a staff of four, supported by high school and college interns.

“Our old trickling filter/RBC plant had trouble meeting winter ammonia limits, and we knew the nutrient removal specs would be more stringent in the future,” says Jason Patty, plant superintendent. “We also had experienced substantial infiltration, and we wanted a plant that could accommodate high-flow conditions. We ended up with an economical and environmentally responsible way to meet all those needs.”

A novel idea

The idea for the wetlands came after El Dorado public utilities director Kurt Bookout toured the wetlands treatment system at the Frontier oil refinery nearby. The city constructed a small pilot wetland at the trickling filter plant, then performed tests on the site for several years, as requested by the Kansas Department of Health and Environment.

“The wetlands showed tremendous potential in removing nutrients during the growing season (April-October), and the water discharged from the wetlands had very low levels of ammonia, TSS and BOD,” says Patty.

Therefore, the city proceeded with a new activated sludge plant that incorporated 20 acres of treatment wetlands. The new plant was built across the river from the old plant, which is now unused. Patty says the city may retrofit it in the future to provide water clarification, filtration and reverse osmosis water for the El Dorado Refinery.

“The water superintendent and public utilities director both have degrees and a background in wildlife biology,” says Patty. “That, combined with their wastewater treatment experience, helped during the new plant’s design stage.”

Designed for savings

The new $10 million plant is designed for a 6 mgd peak flow, and wet-weather maximums of 12 mgd. Flow beyond 6 mgd is either held in a 4.6-million-gallon extraneous flow basin or sent to the 24-million-gallon-capacity wetland cells.

The plant includes an aesthetic 6-acre effluent pond stocked with sport fish and featuring an island and prime fish habitat. A shallow wetland at the southwest corner of the pond acts as a filter and polisher for the effluent before it exits the overflow structure on the way to the Walnut River. The plant also includes:

• New pumps and force main in the existing influent pump station building.

• New headworks building with fine screens (Parkson) and grit removal (Smith & Loveless).

• New biological treatment equipment including mixers (ABS), aerators (Philadelphia Mixing), clarifiers (Hi-Tech Environmental), pumps and instrumentation.

• UV disinfection (Aquionics).

• Solids handling equipment including progressive cavity sludge pumps (NETZSCH), blowers (Kaeser) and centrifuge (GEA Westfalia).

• Oxidation ditch (Philadelphia Mixing).

• New cascade, pump station, scum pump station, water reuse pump system and irrigation system.

The city chose the activated sludge process for its flexibility and efficiency. The wetlands reduced the necessary size of the activated sludge system concrete basin, saving some $2.8 million in construction costs. The plant is fully automated, with automatic backup power, and was designed for expansion to twice its current capacity.

The plant serves about 15,000 people, including 4,800 connections in El Dorado, Butler County Sewer Districts 5 and 15, and the El Dorado State Correctional Facility.

Environmentally friendly

The plant earned the 2008 Project of the Year: Environment Award in the $2 million to $10 million category from the American Public Works Association (APWA). The wetlands purify excess water during high rainfall and in dry weather receive UV-disinfected effluent to keep the diverse vegetation thriving. The effluent flows into the polishing pond and through the wetlands before cascading into the Walnut River.

The wetlands provide habitat for breeding, nesting, feeding and cover for many types of wildlife.

“The whole concept has worked out well for us,” says Patty. “Our existing basin held 4.6 million gallons, and now we have a 24-million-gallon capacity. We use 30 feet of native grass buffer strips, which line the perimeter of our farmland, to protect the Walnut River from sediment erosion and runoff. We also use no-till farming, which prevents erosion and runoff by leaving the residue from the previous season’s crops.”

The biosolids compost process is totally manual. Centrifuge-dewatered sludge is placed in windrows, and wood chips are added. Staff members turn the compost periodically and monitor the temperature. The Class A material fertilizes 260 acres of city-owned land, which is leased to a farmer who plants corn, soybeans and wheat. He splits the gross profit 50-50 with the treatment plant.

“We decided to start composting the biosolids because we used to keep it in a pile before taking it to the fields, and there was an odor issue,” says Patty. “There have not been any odor problems with the compost process.”

Team of four

If all this sounds like a lot of plant to operate, it is. With only four people to do the work, it takes a highly skilled and efficient team to keep the plant running well. Patty, a Class 4 operator, supervises three operators:

• Ron McClure, Class 4.

• Pat Fountain, Class 4.

• Glen Holz, Class 2.

“Right now, we have 2.3 fewer personnel than most plants our size, based on a recent salary survey,” says Patty. “We’re getting it done, but I really need to hire one more operator.” In the meantime, a unique internship program, started in 2007, helps the plant cope with the workload.

Patty started with the plant two months after it came online. McClure, who has 18 years on the job, was on board during the upgrade. Fountain and Holz are fairly new and had no previous experience at an activated sludge plant.

McClure is dedicated to the lab, and all operators rotate on maintenance and composting. Patty conducts ongoing training to stay ahead of the curve and tries to cross-train everyone as much as possible.

“Although my lab technician normally runs the process control tests, I encourage all operators to understand how to do this, so they understand the numbers and can use them to adjust the process if necessary,” he says. “We have more consistency with everyone knowing what’s going on.”

Operators work 7 a.m. to 5 p.m. Monday through Friday, with weekend rotations. A SCADA system allows off-site monitoring. “What makes us successful is the team concept,” says Patty. “It’s not just a biosolids guy or a lab guy, but everyone working as a team to get the job done. They’re proud of the plant and the awards we’ve won.”

Beyond the APWA award, honors include a 2008 Kansas Public City Improvement Award and a 2009 Kansas Water Environment Association Operation and Maintenance Award.

Experiences to share

Patty says the plant’s future success depends on keeping his current employees and finding good ones in the future. “It’s a time-intensive process to find the right people,” he says. “We are promoting the facility and getting people out here to see it, and we’re targeting people with college degrees.”

With a little over three years in operation, the plant is not on too many people’s radars. The city is trying to get the word out that state-of-the-art mechanical treatment plants can be paired with constructed wetlands and save millions of dollars.

Patty stresses that because the industry is always changing, it is important for operators to share their experience. He encourages sharing of ideas and best practices. “We make our conference room available for organizations to conduct training courses related to the industry,” he says. “That gets operators into our plant. We also give tours for city officials and others who want to explore the wetlands/mechanical plant concept.”

El Dorado plans to use the wetlands to enrich environmental education, such as during the annual Walnut River Water Festival. Patty also intends to share this outdoor classroom with biology teachers from the high school and Butler County Community College. “We are continuing to work on species diversification of our wetlands,” he says, “and we may hold classes on that subject as well.”