If you're doing any kind of mechanical work, a parts washer (and on a smaller scale, an ultrasonic jewelry cleaner) is a handy thing to have. But once you remove your now-grease-free part, you're left with a sloppy sludge of solvents in the tank that can't just be poured down the sink. You've got to dispose of the toxic mess, which is both laborious and ultimately bad for the environment, since the stuff has to go somewhere. For professional shops, it's also a line item on the balance sheet, as they typically have to contract with a hazardous waste company to take the stuff away.
A company called CRC (Corrosion Reaction Consultants) Industries has developed a green parts washer that cleans parts without leaving any chemicals behind. Their Smartwasher uses a process called bioremediation, whereby microbes break the oil and grease down into CO2 and water. You do need to use the company's OzzyJuice Cleaning Fluid as the solvent, but it can be reused again and again; the microbes clean the fluid before it flows back into the tank.
Here's how it works, on a chemical level:
1. Oil contaminants enter the solution as parts are washed.
2. Surfactant in OzzyJuice® solution emulsify the oils.
3. Emulsified oil is eaten by the Ozzy® microbe.
4. Oil is converted into water and carbon dioxide.
Here's what it's like to actually use the system, and I've gotta say the UX looks pretty good:
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The company manufactures different sizes and shapes of Smartwasher, including portable units, to fit into a variety of shop situations.
You can learn more about the Smartwasher system here.