1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Turning water into plasma and back in order to purify it

  1. Sep 14, 2014 #1
    This really isnt a HW problem, but this seemed like the best place to post my question.

    Imagine a modern city's water cycle. Clean water is obtained from a river or from groundwater, and this water is used for drinking, bathing and industrial uses. Afterwards the water is fouled biologically and chemically. Next this very dirty water is sealed in a chamber, and a plasma arc (temp of 25,000° C) inside heats it until all of the water and contaminants turn into plasma (all chemical bonds broken).

    Question: If the plasma is allowed to cool, will the heavy atoms form a solid at the bottom of the chamber?

    Question: Will the ionized Hydrogen and Oxygen atoms immediately turn back into water when cooled, or will they be separate gases?
  2. jcsd
  3. Sep 14, 2014 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    There are cheaper, easier and less energy-intensive ways to purify water than heating it to 25,000 C.
  4. Sep 14, 2014 #3
    I didnt mean to imply that the water would be heated all the way to 25,000 C. The water would only have to be heated until it becomes plasma at 3,000 C or so.

    While Im sure your right about cheaper ways to clean water, thats not the whole picture. Cleaning the water is only one benefit of this process. Another benefit is that the contaminants are destroyed. So for example, suppose that we were considering desalinization to produce clean water. The desalinization process concentrates the brine, and then dumps it back into the ocean. At such a concentrated level the contaminants are toxic to ocean life - even though they came out of the sea to begin with. So the area around the plant becomes a dead zone. Heating the dirty water into plasma eradicates all of the biological and chemical residues. Advanced Plasma Power is a company that uses a plasma arc to eradicate solid waste, their process results in a solid leftover that they term Plasmarock. This material can be used in construction. I dont know if a liquid waste process would also produce Plasmarock, thats my first question above.

    Thats also not the end of the process. IF the cooling plasma results in disassociated hydrogen and oxygen gases, then they can be piped into another chamber and ignited. The explosion can be used to move a magnetic piston head, thereby producing electricity (and clean water, because burning the hydrogen and oxygen will cause them to recombine). IF the cooling plasma recombines the water and hydrogen, then the steam can be used to drive a steam turbine/steam generator, which will also produce electricity. So the overall process would look like this:

    Dirty Water
    Energy (Plasma Arc)

    Pure Water
    Energy (Electricity)

    Note that no wastes or contaminants are released, the Plasmarock can be sold, and the energy produced by the process will lower the overall cost. Finally, my process can use the same water indefinitely, so that the city would never run out of water.

    I am interested in feedback, so please let me know if you think the whole process is feasible or not. Thanks.
    Last edited: Sep 14, 2014
  5. Sep 14, 2014 #4


    User Avatar

    Staff: Mentor

    There is no trivial way to separate the individual atomic species from the plasma in bulk. When the plasma cools you won't be able to control how the atomic soup recombines. Shades of the Miller-Urey experiments!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted