ARLINGTON — To Jim Kelly, a simple glass jar of clear water is a compelling example of the value of his work.

“This is untreated raw sewage,” said Kelly, director of the city of Arlington Public Works Department, as he held a glass jar filled with an almost black liquid. “And this is the effluent of our wastewater treatment plant,” he added, holding up the glass jar of clear water. “We’re sending out water into the Stillaguamish River that’s just as clean as what’s already in it.”

On Feb. 28, Kelly submitted a letter of substantial completion to the Arlington City Council for IMCO General Contractors’ upgrades and expansions to the city’s wastewater treatment plant. According to Kelly, once this letter is signed, it will signify that 99 percent of the project has been completed, short of paving and other minor items. Because of ongoing poor weather, Kelly noted that IMCO has been given until the end of its contract in May to complete those items.

This work represents the culmination of efforts that began in 2005, when the city’s wastewater treatment plant was receiving violations due to the city’s dramatic population growth, as well as plans to clean up the Stillaguamish River. After speaking with Kennedy/Jenks Consultants, the designs for the planned upgrades and expansions to the plant were approved by the state Department of Ecology, and construction began in the spring of 2009, three years ago.

Whereas the plant previously existed as a sequencing batch plant, where wastewater went into a big tank and aerated for 36 hours, Kelly summarized the plant’s current process in four steps; physical separation screens, biological nutrient removal, a membrane bioreactor and disinfection through ultraviolet light.

“Our screens sort out grit, rocks, sticks and disposable rags,” Kelly said. “They’re advertised as disposable, but we’re the ones who dispose of them.”

The specific nutrients which the BNR step is intended to remove include nitrogen and phosphorus, both of which deplete the amounts of oxygen available to fish in streams. The four zones of anoxic and aerobic ventilation aerate and remove air from the wastewater to eliminate harmful nutrients while rejuvenating specific types of “bugs” that are ultimately beneficial.

“From there, the MBR relies on micro-filtration to get the water as clear as you saw it,” Kelly said. “The membrane pores are finer than the hairs on your head.”

The treated water still needs to be subjected to ultraviolet light to kill off the last of the “bugs” in the effluent before it reaches the Stillaguamish River.

“You wouldn’t want to go in that chamber to get a tan,” Kelly laughed. “And fortunately for us, the bugs don’t have sunscreen to give them UV protection.”

This still leaves behind the waste extracted by the MBR, which is sent to an aerobic digester for 10 days. The “bugs” in the waste eat the organics to transform them into biosolids, which in turn become compost, which is used on city property ranging from parks and athletic fields to the cemetery.

“Our biosolids come in 1 to 2 percent solid, and they leave 17 to 18 percent solid,” Kelly said. “They go into dump trucks, get mixed with hog fuel and come back to us as compost. It’s a big process, but once you break it down, it’s really quite simple.”

Of the total $34.5 million price tag for the plant’s upgrades and expansions, $29.5 million went toward construction, while the rest covered the costs of permitting, preliminary engineering and design, and construction management. Funding sources included three loans from the public works trust fund, one loan each from the state revolving fund and the American Recovery and Reinvestment Act, one grant from the ARRA and monies from sewer capital reserves. Part of the recently approved stormwater utility rate increases will also go to support the plant’s upgrades and expansions.

“We need to cover our increased capacity and technology,” Kelly said. “The increased capacity is covered by the population growth itself, but we still need to pay for the technology. If you look in USA Today, you’ll see an article about the scarcity of water. What we’re doing parallels what’s being done by cities from Los Angeles to Singapore.”