Water recycling technologies developed for space are helping a parched American west

But even aboard the ISS, we have yet to create a fully-closed reuse system.

Johnson Space Center - NASA

Whether you live in the rapidly drying American West or are aboard the International Space Station for a six-month stint, having enough water to live on is a constant concern. As climate change continues to play havoc on the West’s aquifers, and as humanity pushes further into the solar system, the potable supply challenges we face today will only grow. In their efforts to ensure humanity has enough to drink, some of NASA’s cutting-edge in-orbit water recycling research is coming back down to Earth.

On Earth

In California, for example, the four billion gallons of wastewater generated daily from the state’s homes and businesses, storm drain and roof-connected runoff, makes its way through more than 100,000 miles of sewer lines where it — barring obstructionist fatbergs — eventually ends up at one of the state’s 900 wastewater treatment plants. How that water is processed depends on whether it’s destined for human consumption or non-potable uses like agricultural irrigation, wetland enhancement and groundwater replenishment.

The city of Los Angeles takes a multi-step approach to reclaiming its potable wastewater. Large solids are first strained from incoming fluids using mechanical screens at the treatment plant’s headworks. From there, the wastewater flows into a settling tank where most of the remaining solids are removed — sludged off to anaerobic digesters after sinking to the bottom of the pool. The water is then sent to secondary processing where it is aerated with nitrogen-fixing bacteria before being pushed into another settling, or clarifying, tank. Finally it’s filtered through a tertiary cleaning stage of cationic polymer filters where any remaining solids are removed. By 2035, LA plans to recycle all of its wastewater for potable reuse while Aurora, Colorado, and Atlanta, Georgia, have both already begun augmenting their drinking water supplies with potable reuse.

“There are additional benefits beyond a secure water supply. If you're not relying on importing water, that means there's more water for ecosystems in northern California or Colorado,” Stanford professor William Mitch, said in a recent Stanford Engineering post. “You're cleaning up the wastewater, and therefore you're not discharging wastewater and potential contaminants to California's beaches.”

Wastewater treatment plants in California face a number of challenges, the Water Education Foundation notes, including aging infrastructure; contamination from improperly disposed pharmaceuticals and pesticide runoff; population demands combined with reduced flows due to climate change-induced drought. However their ability to deliver pristine water actually outperforms nature.

“We expected that potable reuse waters would be cleaner, in some cases, than conventional drinking water due to the fact that much more extensive treatment is conducted for them,” Mitch argued in an October study in Nature Sustainability. “But we were surprised that in some cases the quality of the reuse water, particularly the reverse-osmosis-treated waters, was comparable to groundwater, which is traditionally considered the highest quality water.”

The solids pulled from wastewater are also heavily treated during recycling. The junk from the first stage is sent to local landfills, while the biological solids strained from the second and third stages are sent to anaerobic chambers where their decomposition generates biogas that can be burned for electrical production and converted to nitrogen-rich fertilizer for agricultural use.

New York, for example, produces 22,746 tons of wastewater sludge per day from its 1,200-plus statewide wastewater treatment plants (WWTPs). However, less than a tenth of plants (116 specifically) actually use that sludge to produce biogas, per a 2021 report from the Rockefeller Institute for Government, and is “mainly utilized to fuel the facilities and for the combined heat and power generation of the WWTPs.”

Non-potable water can be treated even more directly and, in some cases, on-site. Wastewater, rainwater and greywater can all be reused for non-drinking uses like water the lobby plants and flushing toilets after being captured and treated in an Onsite non-potable water reuse system (ONWS).

diagram of water reuse in a modern multi-unit building

“Increasing pressures on water resources have led to greater water scarcity and a growing demand for alternative water sources,” the Environmental Protection Agency points out. “Onsite non-potable water reuse is one solution that can help communities reclaim, recycle, and then reuse water for non-drinking water purposes.”

In Orbit

Aboard the ISS, astronauts have even less leeway in their water use on account of the station being a closed-loop system isolated in space. Also because SpaceX charges $2,500 per pound of cargo (after the first 440 pounds, for which it charges $1.1 million) to send into orbit on one of its rockets — and liquid water is heavy.

ISS Water System

While the ISS does get the occasional shipment of water in the form of 90-pound duffle bag-shaped Contingency Water Containers to replace what’s invariably lost to space, its inhabitants rely on the complicated web of levers and tubes you see above and below to reclaim every dram of moisture possible and process it into potability. The station’s Water Processing Assembly can produce up to 36 gallons of drinkable water every day from the crew’s sweat, breath and urine. When it was installed in 2008, the station’s water delivery needs dropped by around 1,600 gallons, weighing 15,960 pounds. It works in conjunction with the Urine Processor Assembly (UPA), Oxygen Generation Assembly (OGA), Sabatier reactor (which recombines free oxygen and hydrogen split by the OGA back into water) and Regenerative Environmental Control and Life Support Systems (ECLSS) systems to maintain the station’s “water balance” and supply American astronauts with a minimum of 2.5 liters of water each day. Cosmonauts in the Russian segment of the ISS rely on a separate filtration system that only collects shower runoff and condensation and therefore require more regular water deliveries to keep their tanks topped off.

ISS Water System 2

In 2017, NASA upgraded the WPA with a new reverse-osmosis filter in order to, “reduce the resupply mass of the WPA Multi-filtration Bed and improved catalyst for the WPA Catalytic Reactor to reduce the operational temperature and pressure,” the agency announced that year. “Though the WRS [water recovery system] has performed well since operations began in November 2008, several modifications have been identified to improve the overall system performance. These modifications aim to reduce resupply and improve overall system reliability, which is beneficial for the ongoing ISS mission as well as for future NASA manned missions.”

One such improvement is the upgraded Brine Processor Assembly (BPA) delivered in 2021, a filter that sieves more salt out of astronaut urine to produce more reclaimed water than its predecessor. But there is still a long way to go before we can securely transport crews through interplanetary space. NASA notes that the WPA that got delivered in 2008 was originally rated to recover 85 percent of the water in crew urine though its performance has since improved to 87 percent.

BPA diagram

“To leave low-Earth orbit and enable long-duration exploration far from Earth, we need to close the water loop,” Caitlin Meyer, deputy project manager for Advanced Exploration Systems Life Support Systems at NASA’s Johnson Space Center in Houston, added. “Current urine water recovery systems utilize distillation, which produces a brine. The [BPA] will accept that water-containing effluent and extract the remaining water.”

When the post-processed urine is then mixed with reclaimed condensation and runs through the WPA again, “our overall water recovery is about 93.5 percent,” Layne Carter, International Space Station Water Subsystem Manager at Marshall, said in 2021. To safely get to Mars, NASA figures it needs a reclamation rate of 98 percent or better.

But even if the ISS’s current state-of-the-art recycling technology isn’t quite enough to get us to Mars, it’s already making an impact planetside. For example, in the early 2000’s the Argonide company developed a “NanoCeram” nanofiber water filtration system with NASA small business funding support. The filter uses positively charged microscopic alumina fibers to remove virtually all contaminants without overly restricting flow rate, eventually spawning the Oas shower from Orbital Systems.

“The shower starts with less than a gallon of water and circulates it at a rate of three to four gallons per minute, more flow than most conventional showers provide,” NASA noted last July. “The system checks water quality 20 times per second, and the most highly polluted water, such as shampoo rinse, is jettisoned and replaced. The rest goes through the NanoCeram filter and then is bombarded with ultraviolet light before being recirculated.” According to the Swedish Institute for Communicable Disease Control, the resulting water is cleaner than tap.

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