Developing a metropolitan wastewater treatment plant capable of meeting the most stringent water quality standards anywhere is a daunting challenge, but being able to design it from scratch is an enticing opportunity, says the man who's responsible for overseeing the building of Spokane County's planned $148 million facility here.

David Moss, the county's water reclamation manager, says that while treatment plants around the country have been faced with expanding to meet new demand and retrofitting to meet new water-quality rules, Spokane County will design its new facility from the ground up, without having to adapt state-of-the-art science to older infrastructure.

Currently, about 50 people at CH2M Hill Inc.'s Corvallis, Ore., office are busy designing the facility, which will be located in east Spokane and is expected to become operational in early 2012, Moss says.

CH2M Hill was hired by the county to design, build, and operate the facility. The company referred questions about its design back to Spokane County.

Moss says that while constructing a water reclamation facility capable of processing 8 million gallons of sewage a day—and of being expandable to handle 24 million gallons a day—has plenty of inherent challenges, perhaps the biggest is the need to meet rules regarding phosphorus.

"Phosphorus is one of the key bad actors in freshwater," says Moss, who is serving as the county's project manager for the new facility.

Phosphorus is a nutrient that promotes algae growth and thus depletes oxygen needed by fish. New state rules would require the planned plant to remove nearly all of the phosphorus contained in the sewage it treats before releasing the treated effluent into the Spokane River.

That will require careful engineering and use of new, expensive technologies, Moss says.

While the county will own the facility and will hold the environmental permits under which it will operate, the county doesn't have the expertise to run such a sophisticated plant, Moss says. He says it will be up to CH2M Hill to employ technologies to meet the standards.

"The system takes waste and uses physical, chemical, and biological processes to treat the water so it is reusable," Moss says.

CH2M Hill started the formal design phase of the project in January, and is scheduled to complete that process by the end of this year, he says.

Moss says the plant will focus on reducing what's called "total phosphorus." There are multiple kinds of phosphorus, he says, with different characteristics. Total phosphorus includes all types of phosphorus, he says.

The Washington state Department of Ecology says that one pound of phosphorus can grow 700 pounds of algae. When algae plants decompose, that uses up oxygen in the water, hurting fish populations, it says.

Moss says the phosphorus discharge limits that will be in place when the plant comes online will be among the most stringent in the world.

Sewage flowing into the plant is expected to contain phosphorus levels of about 5,000 to 7,000 micrograms per liter, Moss says. After treatment, water released by the plant into the Spokane River—about a mile to the north—will need to have average phosphorus levels of just 50 micrograms per liter, he says. That limit would be based on a seasonal average, from April to October, he says.

When untreated sewage arrives at the facility, it will first move through screens that will remove large inorganic material, and then it will go through a grit removal process to take out sand and gravel. The organic solids and liquid will move on to what Moss calls chemically enhanced primary treatment, where the suspended material that didn't screen out settles to the bottom, and liquids are sent one way and solids another.

The bio-solids will be sent to anaerobic digesters for more treatment, and then will be pumped to centrifuges where more moisture will be spun out, and the remaining material eventually will be used in agricultural products such as fertilizer, mostly for grains, Moss says.

More than other plants, the county's new plant will focus on the chemical reduction of phosphorus, Moss says. The facility will work to bind phosphorus to solids.

During the separation process, methane gas will be produced, and it will be burned to produce electricity to help run and operate the plant.

The liquids, after going through the chemically enhanced primary treatment and being separated, will be diverted to a large aeration basin, where microorganisms will be added to metabolize contained waste. From there, the effluent will be pumped into a building where it will be forced through what are called hollow-fiber ultrafiltration membranes, which look like tightly woven fishing line and will help remove phosphorus, he says. Then the treated water will be chlorinated and de-chlorinated before being piped to the Spokane River, just east of Spokane Community College. The water also could be used for irrigation, industrial use, groundwater recharge, or wetland creation or restoration, he says.

Although the process will be state of the art, it won't use what's called reverse osmosis, which is used in some treatment plants in places such as Honolulu and Saudi Arabia. That system can eliminate even more phosphorus, but currently is too expensive to implement, Moss says.

Meeting capacity needs

The county's plant will be located at the 20-acre former stockyards site near Freya Street and Trent Avenue, just inside the eastern city limits of Spokane. The county bought the property in 2004. It's needed to supplement the capacity of the city of Spokane's 44-million-gallon per day wastewater treatment facility located in the northwest part of the city. The county's new plant will be about a fifth that size, Moss says.

The city plant treats sewage for Spokane County under contract, and the county is guaranteed 10 million gallons per day of the city plant's capacity, for which the county pays nearly $5 million a year, Moss says. The county expects to reach its 10 million gallon limit as early as 2013, so having the new facility operational by 2012 will be necessary, Moss says.

Even after the county's new plant is operational, the county will continue to send wastewater to the city plant, he says. Having its own plant, Moss says, will enable the county to meet expected growth in sewer hookups for an estimated 20 years, which also is the expected lifespan of the infrastructure in the planned new plant.

The county wants to be able to accommodate thousands of new sewer connections as a result of its extensive septic tank elimination program, which is intended to protect the Spokane-Rathdrum Aquifer, Moss says.

The cost of the new facility and associated projects and programs—together now totaling nearly $280 million—has risen substantially from earlier estimates, he says. Most of the increase is due to the new, stringent environmental regulations and discharge permit limits that will be applied to the plant by the Department of Ecology and the U.S. Environmental Protection Agency, he says.

CH2M Hill will be paid roughly $140 million to design and build the facility, and about $6 million a year, or $120 million over its 20-year contract, to operate it, Moss says. HDR Engineering Inc., of Spokane, will serve as the county's engineering consultant during design and construction, observing the process and making sure the county's questions get answered, Moss says.

The project will be funded in part through a $75 million loan from Ecology. The rest will be funded through general obligation bonds. Both the loans and bonds will be repaid over 20 years through fees paid by users of the plant, Moss says. Increased sewer rates already have been proposed to pay for the project.

Moss says that because it's a design-build contract, the project's construction schedule will be shortened and costs will end up being 10 percent to 15 percent lower than if contractors had been hired separately to design and build the facility.

Even though the design won't be final until later this year, CH2M Hill already has started construction on the plant site, including installation of some foundations for structures, particularly those with deep foundations, such as the anaerobic digesters and aeration basin, Moss says.

Long in the works

Long before CH2M Hill began final design on the project, the county went through an eight-year planning and preliminary design phase, ending in 2007, Moss says. During that phase, planners discussed, among other things, where to locate the facility, who would own it, and who would operate it, he says.

The process began in 1999, when the county began working to ensure that sufficient wastewater treatment capacity was available to complete its septic tank elimination program, he says. The county says more than 25,000 septic tanks in its urban growth area have been removed so far, and an additional 9,000 septic systems will be removed by the time the program is completed in 2015.

The facilities planning process identified and evaluated several alternatives to handle wastewater, ranging from expanding capacity at the city of Spokane's wastewater treatment plant, to constructing new treatment facilities in various parts of the county. Options for other system components were also evaluated.

Meanwhile, since 2003, Ecology and the EPA have been exploring ways to improve water quality in the Spokane River and Lake Spokane to meet the federal Clean Water Act.

The river and lake contain excessive amounts of phosphorous and other nutrients that trigger algae growth and deplete dissolved oxygen in the river and lake, Moss says.