Wastewater treatment plant nearing completion
By GEORGE LEDBETTER, Record Editor Tuesday, December 01, 2009
Two years after the Chadron City Council decided to replace the city’s wastewater lagoons with a mechanical treatment system, the new, $4 million sewage plant is expected to undergo preliminary testing in the next few weeks.
But full operation of the new system, which uses forced air to speed up the same biological processes used in the existing lagoons, probably won’t begin until the first part of next year, after all of the equipment has been tested and water department personnel have been fully trained, according to Public Works director Milo Rust.
Fisher Construction, general contractor for the project, began work on the plant in April, with a contract that allows a full year until final completion. Installation of ultraviolet (UV) lights that are the last stage of the treatment process and are only used in summer months, will be one of final phases of construction, said Rust.
Although Chadron has known for almost a decade of the need to upgrade its sewage treatment system to meet state and federal environmental standards that are more stringent now than when the lagoons were built in 1962, the decision to build the new plant didn’t come easy. The council’s decision in November, 2006 to build a mechanical plant instead of expanding the passive lagoon treatment system was a 3-1 split vote, with dissenting council member John Gamby expressing concern about the long term cost of maintaining equipment in the new facility.
But other council members were persuaded to abandon the lagoon system after Baker and Associates, the city’s engineers for the project, said their analysis showed that the mechanical plant would cost about $2 million less over 20 years.
The city treats just over 600,000 gallons of wastewater per day, said Rust. The existing system uses lagoons, located on about 140 acres of land northwest of town, to hold the water while bacteria break down the wastes. After treatment the water is used for irrigation by a private landowner downstream from the plant, and doesn’t enter the White River, which is about a mile away.
A Kansas-based company called AeroMod designed the new treatment facility, which is based on the firm’s advanced technology for clarifying wastewater. “It (the design) is fairly new,” said Rust. “We toured four plants that have their design.”
Treatment in the new plant begins with a ‘stair screen’ device that removes solid trash from the wastewater before it enters an network of interconnected concrete tanks, where natural bacteria breakdown wastes in an aerobic (with oxygen) process.
The difference between the lagoons and the mechanical process is the use of compressed air to speed up the digestive action of the bacteria. The AeroMod system introduces the air through a network of plastic pipes and uses few moving parts under the water, which means less maintenance costs, the company website notes.
The design also draws off sludge, the semi-solid residue remaining after treatment, from a level above the layer in which the waste eating ‘bugs’ thrive, noted Rust.
Sludge build up on the bottom of the treatment lagoons was one factor in reducing their ability to handle the city’s wastewater effectively. And the existing ponds didn’t have the capacity to treat the city’s water to current discharge standards, Rust said. “We had 40 acres of lagoons. To meet the new requirements, we would have needed 100 acres. We just outgrew them...They weren’t working.”
The expense of building new lagoons would have been quite high, noted Rust, because current regulations require that they be lined with an impermeable material to prevent contamination. “The lining is a big cost and we would have had to build another 50 acres of lagoons,” he said. “That’s the difference in the cost (between the mechanical and lagoon systems).”
After the clarified water leaves the tanks it passes through a final purification process-exposure to ultraviolet rays-before it is discharged into the intermittent stream channel that leads to the White River.
The UV treatment isn’t required in winter, however, said Rust. “From November to April we don’t have to discharge to UV. In summer they require it.”
Not all of the water that enters the plant is discharged into the stream bed. Sludge from the operation will be used on site for irrigation of alfalfa, said Rust. The city has about 80 acres of land that can be used for that purpose, he said.
When the new plant is complete, the wastewater will be clean enough to meet federal water quality standards as it leaves the treatment plant site, said Rust. At present the water that flows through the lagoon doesn’t meet the standards for discharge into the White River, noted Rust. That hasn’t been a problem, because all the water had been used for irrigation, but city still bore responsibility for the water until it was used, he said. With the new system, the city’s responsibility ends when the water is discharged to the stream bed.
Treated water from the new plant will also be suitable for crops, said Rust. “It’s not determined if it will still be used for private irrigation,’ he said.
The city has drawn on a state revolving loan fund, as well as money from the federal economic stimulus program, to pay for construction of the new plant. It also began increasing charges to residents for the last several years, in anticipation of the expense of building and operating the new plant
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Chadron Public Works Director Milo Rust shows the valve handle that controls water flow into the new wastewater treatment plant.
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