April 23, 2020 0 Comments
The average human uses 10 Gal a day of water to; drink, prepare their food, wash and clean. In some countries could be up to 50 Gallons a day. We all give for granted that we open the faucet and the water will come out, ready for consumption. However, there are places where the water is not so easily available or, it is not ready for human consumption. With that said, in other places, there are humans living with less than 1 Gal of water a day. I am talking about hard working humans, living and working in a very harsh environment.
The work they are doing is very valuable and is supported by organizations with very large budgets. You would think that all they need is to figure out how to transport water to that location. Unfortunately, transporting 1 Gal of water to this environment can cost around $270,000. That is correct, it is 270,000 USD per Gallon.
We are talking about the astronauts working in the International Space Station (ISS). The cost of bringing anything to the ISS is almost $75,000/kilogram. To keep the water supply, NASA pays $1.6M/day to make sure 6 astronauts have enough water to live and work in space.
Fortunately for these astronauts, and NASA, the other 9 Gals of water needed by each astronaut every single day, is recycled from the humidity in the air inside ISS and, urine. No kidding, urine is recycled and mixed with the rest of the water ready for consumption.
Although the technology used to achieve this scientific, and technological feat, is the same one used on earth to recycle water, the difference is; the cost of transporting 1 Gal of water on earth is thousands of times lower. This means that, although the technology exists, there is no economic incentive to use it to quench our thirst.
How does the ISS recycle water? The Environmental Control and Life Support System (ECLSS) is a regenerative life support unit that provides clean air and water to the International Space Station’s crew and laboratory animals, through artificial means. There are three main sources of recyclable water; humidity in the air inside the station, urine, and waste from Extra Vehicular Activities (EVAs).
Image provided by NASA: The Environmental Control and Life Support System (ECLSS)
The ECLSS consists of two key units; the Water Recovery System (WRS) and the Oxygen Generation System (OGS). The recirculating air goes through the Air Revitalization System (ARS) which is dedicated to cleaning the air. This involves removing trace contaminants produced by electronics, plastics and human off-gassing, including carbon dioxide exhaled by the crew during normal respiration. Trace contaminants are removed by flowing cabin air through three separate units including an activated charcoal bed, a catalytic oxidizer and a lithium hydroxide bed. Carbon dioxide is removed using molecular sieves, materials that separate and capture gases based on their size.
Humidity on board the ISS is kept at around 60% RH. The Temperature and Humidity Control (THC) makes sure that the air circulates throughout the station. That way, moisture does not build up anywhere (high humidity spots can grow mold and other living colonies). Humidity is controlled on board the ISS by the heat exchangers that are part of the Active Thermal Control System (ACTS). As air passes through the heat exchangers and is cooled, the water in the air condenses. The water is then collected so it can be sent to the Water Recovery System (WRS).
The CO2 removed from the air, will be sent to the CO2 Reduction System (CRS) where will be reacting with Hydrogen coming from the Oxygen Generation System (OGS), to generate water and methane. The methane is vented into space and the water is sent to the WRS.
At the WRS is where things get interesting for us. Here is the urine and other water waste is processed and the technology used to do so is of interest to us and hopefully to you too.
The WRS has two section; The Urine Processor Assembly (UPA) and the Water Processor Assembly (WPA). And the two waste streams are processed differently. However, at the end they are combined for a final polishing and back to the storage tanks for reuse.
Image provided by NASA
The UPA sends the urine through a process call Vapor Compression Distillation. This is basically a distillation process where the urine is boiled, and the vapor send through a condensation system. End result is a very concentrated urine in one end and clean distilled water on the other. On earth is easy to achieve and we can imagine how it works. However, in space, things are different as there is no gravity. Remember, water does not stay down, and vapor goes up. It is all floating around in a zero-gravity dance. So how do you separate water and vapor? The bright minds at NASA decided to use centrifugal forces to create gravity, strong enough to keep liquid down and let vapor go up.
The rotating distilling unit is a marvel of ingenuity that allows fluid and gases to separate in space. Keep that in mind as it will be helpful further in the recycling process. In the meantime, the concentrated urine (brine) is sent to the Brine Processor Unite. In this unit heat is used to further concentrate the brine and release water vapor. The water vapor goes back to the Air Revitalization Unit and the concentrated urine, now solids, are packed for disposal with the rest of the waste sent back to burn in the atmosphere when the Progress spaceship reenter the atmosphere.
Now that we have the urine taken care of, we can take all the available wastewater and process it for reuse. To keep the articles limited in size, we will follow this process in our next article. See you then!
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