Summary
The authors describe "Electro-Clean", a way to make hypochlorous acid disinfectant by electrolyzing salt water with carbon rods and a 5 volt DC power supply. A 90-minute batch makes about 1.35 to 1.5 liters at roughly 800 to 1000 ppm free chlorine, which is diluted to about 250 ppm for surfaces and adjusted to pH 6 with vinegar. They tested it in India, Mexico, Nigeria and Uganda.
Key points
- The build: a 1.5 liter soda bottle, two carbon rods, a 5 V DC supply and a multimeter. The electrolyte is 30 g per liter of non-iodized salt in tap water. A batch runs 90 minutes at about 5 A.
- Output: 915 to 962 ppm free chlorine in lab batches, and 259 to 1377 ppm across the other countries' setups.
- pH: electrolysis leaves the solution alkaline. After diluting to about 250 ppm, vinegar brings it to pH 6, which took about 28 mL of 5% vinegar per 1.35 liters in the lab test.
- In Mexico and India tests, the 250 ppm solution disinfected surfaces about as well as 1% bleach and 70% ethanol.
- Storage: free chlorine fell by under 5% in 34 days without vinegar, and by 16 to 20% with it.
- Cost: about US$42 to build in the United States. Operating cost was about US$0.15 per liter at 800 ppm. The rods lasted about 90 hours of running, or sixty 1.35 liter batches.
- Chlorine exists mostly as dissolved gas below pH 4, which is why the pH is set after electrolysis.
- Funding: partial support from the Balaton Group and the Rudd Chair funds of one author, and two Mexican technological institutes. The authors report the funders had no role in the study.