The Printable Mixed Oxidant Generator is in the very early stage of development. There is a great deal of experimentation and research that needs to be performed; however, I put it on Appropedia in the hopes that some interest will be stimulated, and other might help explore this. Commercial models can be found here. Mixed oxidants are powerful oxidizers, and can be used to sterilize water. The oxidants will effectively decompose any organic molecule, which includes virus and bacteria. Full details at Thingiverse available here. The Printable Mixed Oxidant Generator was created at Queen's University by John Van Tuyl as an entry into the 3-D Printable Open Source Appropriate Technology Design Competition.
In this reaction, a saturated solution of aqueous sodium chloride (NaCl) is used as the electrolyte in an electrolytic cell. The reaction is accomplished by running a current through the cell. Two electrodes, the anode (-) and a cathode (+), act to conduct electricity into the electrolyte. Oxidation of ions occurs at the anode, where the ion passes an electron to the anode. Reduction of ions occurs at the cathode, where the ion gains an electron. The anode electrode is coated with a specially selected electro catalyst. This substance is in its oxidized state, or is inert, in order to stop further oxidation of the anode in the reaction. This forces molecules in the solution to oxidize. Hydroxyl molecules, as well as Cl molecules form. The molecules Cl2, HOCl and OCl- have been found to be key oxidants in the disinfection process. The electrolysis of water will also produce .OH, O3, H2O2, and .O2-. When added to water, these oxidants can be used to destroy bacteria, virus, and some organic compounds. In addition to oxidants, some perchlorates will form. This is potentially dangerous; however their formation will be less than the oxidants and will probably not pose a major issue.
Selection of the catalyst is crucial. Most of the anodes that are suggested for this reaction are expensive and rare. The most commonly explored catalysts are Pt, titanium and a transition metal oxide, and boron doped diamond (BDD). Tin oxide was selected as the most appropriate anode. Tin has a high oxygen overpotential, meaning that it hinders the evolution of oxygen at the anode, reducing wasted energy. Tin oxide also shows a good elect catalytic ability towards the production of hydroxyl radicals, .OH, which is a powerful oxidant, and instrumental in the formation of other oxidants. Most importantly, "tin plate" is commonly used in making food containers and is therefore easily accessible.
- The current rough design uses the evolution of hydrogen and oxygen to meter the reaction. A manometer is built into the product in order to measure these gasses. In a normal electrolytic cell, one would expect twice the volume of hydrogen as oxygen to evolve. However, when oxidants are being generated, the ratios will vary. I hope to be able to take advantage of these differences in order to determine when enough oxidants have been formed to effectively sterilize a desired amount of water. The oxidant containing solution is simply poured into the contaminated water; much like bleach can be used to sterilize water. I am experimenting to determine if this is possible.
License[edit | edit source]
This is for anybody who wants to try it, and has a 3D printer available. I encourage you to modify it, and update this page with what you have found.
Instructions[edit | edit source]
- Print on something like a RepRap. Use maximum infill to prevent porosity, which could cause leakage and loss of suction.
- This is a one piece print. Just set it and forget it.
- Cut electrodes out of tin plate to fit into the electrode slot. They can be heated to seal them.
- Pour a saturated brine solution into the holding tank.
- Apply a current across the electrodes. The suitability of the tinplate as an electro catalyst, the amount of current to apply, and the ability to measure the level of oxygen and hydrogen evolved with a high enough resolution are the main issues. Please explore these issues!
References[edit | edit source]
- H. Son; M. Cho; J. Kim; B. Oh; H. Chung; J. Yoon, Enhanced disinfection efficiency of mechanically mixed oxidants with free chlorine, 2005. Water research. 39. p 721-727. .
- Loge, Frank J; Inouye, Trevor; Watts, Richard J, Disinfection of Secondary Effluents Using Tin Oxide Anodes, 2006. Water Environment Research. 78. p 41-48. .