Interestingly you can design a wastewater treatment plant in arizona without a PE license, but there are no exemptions for any type of engineering except that which would be done by a civil or structural engineer.[0] At the same time though, the word "engineer" in isolation is not protected in Arizona the way it is in some other states.[1]

[0] https://codes.findlaw.com/az/title-32-professions-and-occupa...

[1] https://codes.findlaw.com/az/title-32-professions-and-occupa...