Six cleaning methods — the dishwasher, microwave, and washing machine; bleach, ammonia, and vinegar soaks — to see which removed the most bacteria.
The bleach solution killed 99.9 percent of the three bacteria strains from all our test sponges (scrub and regular cellulose), a benchmark based on the EPA's requirement for sanitization of non-food-contact surfaces. Mix 3/4 cup of bleach in one gallon of water, and soak the sponge for five minutes. The microwave and the dishwasher were the next most effective, zapping 99.9 percent of germs from the home-used sponges and from the lab-treated scrub sponges. However, on the lab-treated cellulose sponges, microwaving just missed the mark for E. coli (99.83 percent reduced), and the dishwasher didn't quite get all the salmonella or E. coli (99.88 and 99.86 percent reduced, respectively). Put a sponge into a regular dishwasher load, using the "heated dry" setting. In the microwave, saturate the sponge (we used 1/4 cup of water for scrub sponges and 1/2 cup for cellulose); heat on High for one minute (scrub) or two minutes (cellulose). Keep an eye on it. Clean sponges weekly, and toss shabby ones.
A five-minute soak in full-strength vinegar averaged 99.6 percent bacteria elimination; in full-strength ammonia, 97.0 percent. The washing machine proved least effective, killing on average 93.0 percent of bacteria.
