Wastewater technology may one day solve the world’s thirst for freshwater and provide an environmentally safe means for biosolids disposal.

Brad Hill, utilities director for the City of Flagstaff, Arizona, says like most municipalities in the parched Southwest, managing the use of water supplies is critical, as well as planning for and securing sources for long-term needs.

“Flagstaff has a robust history of managing the supplies we have today through water conservation,” he says. “Ever since our city council adopted its first water conservation ordinance in 1988, per capita water use has declined over the past 25-plus years. In fact, the total gpcd (gallons per capita per day) water use has declined from 189 gpcd to 108 gpcd in 2014, one of the lowest of any municipality in the state.”

In 2011, the city conducted a Water Resources Master Plan (scheduled for updating this year) that identified future locally derived as well as imported water supplies and evaluated their relative costs per acre-foot.

Examples include the expanded use of reclaimed water beyond current irrigation (commercial and manufacturing) such as advanced treatment for indirect potable reuse.

“The city has been a leader in Arizona using reclaimed water since the mid-1970s,” Hill says. “Reclaimed water now makes up about 20 percent of the total volume of water we directly deliver to our customers.”

Citizen group offers ideas
Joining the discussion is a citizens group, comprised of five engineers and scientists. Known as the Flagstaff Water Group, it believes continued conservation and new technologies offer hope for the future and at far less expense than the estimated $200 million it would cost to build a pipeline from wells at Red Gap Ranch to Flagstaff, about 30 miles away.

According to FWG, increasing conservation by half a percent a year has the potential to extend the city’s current water supply by nine to 30 years.

The group also says technology has the potential to purify Flagstaff’s wastewater to drinking water standards and reduce or eliminate the biosolids that remain.

“Our group has advocated that the City of Flagstaff research the emerging technologies for wastewater treatment; however, we are not endorsing any product, only the process to better clean reclaimed water,” says FWG member Bryan Bates, science professor at Coconino Community College in Flagstaff.

One such technology, developed by Gate 5 Energy Partners of California, dries and pulverizes sludge into powdered biofuel. Burned to power the drying process, excess steam is used to produce electricity.

Steve Delson, co-founder and CEO for Gate 5, describes his company’s technology as thermal oxidation. The system can handle from 6 to 120 wet tons of biosolids per day.

Formed in 2011, Gate 5 is in the fundraising stage of constructing a working model that could process 5 to 6 mgd and be trailer-mounted or installed at a treatment plant.

“Everything’s been tested at a commercial scale, but we don’t have a fully integrated, operational system yet,” says Delson, who has contacted about a half-dozen municipalities, mostly in Southern California.

A system that could process 6 to 8 wet tons of sludge would cost about $5 million and have an estimated payback of three to five years. What makes the Gate 5 technology unique is its scalability and the transformation of biosolids into usable products such as renewable energy, heat and water, he says.

“The inert ash that’s left over after combustion can be used as a building material. And because it’s produced without any fossil fuel, it can be a LEED concrete or asphalt additive.”

The Flagstaff Water Group also had been in contact with HTI (Hydration Technology Inc.), a forward osmosis filtration products company based in Corvallis, Oregon.

Future of reuse
Keel Robinson, North America Water Reuse Leader for water technology company Xylem, says municipalities already have a wide range of indirect potable reuse filtration and disinfection technologies to choose from including microfiltration, ultra-filtration, reverse osmosis and advanced oxidation.

“One of the technologies we’re working with right now in California is advanced oxidation using Wedeco’s MiPro photo Advanced Oxidation Process,” he says. “In this case we’re using UV light with either hydrogen peroxide or chlorine to remove pathogens and trace contaminants that can’t be removed by another means. This technology is the final treatment barrier for indirect potable reuse.”

Robinson says California is in the process of developing guidelines for direct potable reuse by the end of 2016.

“The WateReuse Association and the State of California believe the only way we’re going to reach our water reuse goal and solve the water scarcity issue is with direct potable reuse,” he says. “The reason is wastewater is available in the urban environment. If we can treat it at the point of use and get it directly over to a water treatment plant, that’s less expensive than having to pipe water long distances to a reservoir. It’s even cheaper than non-potable reuse where you have to build a distribution pipe to get it throughout the city.”

Reverse osmosis, considered the best available technology for direct potable reuse, can be a disposal challenge because of the 20 percent brine stream it produces.

“If you’re in coastal California, you can put it back into the ocean,” Robinson says. “But if you’re inland, what do you do with the stream?”

The answer might be ozone-enhanced biologically active filtration, a process being evaluated in many states that disinfects, removes trace contaminants and destroys the organic carbon in water without producing a significant waste stream or using large amounts of energy like reverse osmosis.

Robinson says what makes water reuse an attractive solution to today’s water needs is its resistance to drought.

“We’re always going to generate wastewater,” he says. “Unlike our traditional water resources that are stressed by dry weather and population growth, wastewater is a drought-resistant water resource that is too valuable to waste.”