4

I recently purchased some 55 gallon blue barrels for rainwater harvesting. Upon closer inspection of the barrels, I noticed they previously housed food grade sodium hypochlorite which was used to wash produce. I was searching for food grade barrels but wasn't expecting bleach. Because I will be watering plants and fruit tress with the rainwater, I don't want the water chlorinated which would kill the bacteria I'm trying to promote in the soil. These barrels are empty but I was advised to rinse them when I initially purchased them.

Can I assume that just rinsing with water won't completely get rid of the bleach and that the residual bleach which may be on the walls of the barrel will not decompose or neutralize by itself?

If I were to wash the barrels with water and Hydrogen Peroxide, will this suffice to remove the chlorine?

ringo
  • 24,013
  • 6
  • 87
  • 135
brian
  • 41
  • 3

2 Answers2

5

Several good tap water rinses should probably get rid of any significant remaining amounts of bleach, although it's possible some bleach residues might adsorb to the wall of the barrel and resist these efforts.

Per here and here, if you want to be very sure the residues are removed, dissolve a handful of vitamin C (ascorbic acid) tablets in water and use that to rinse the barrels until all bleach odor is gone. The ascorbic acid will act as a reducing agent and should reduce the bleach levels to next to nothing.

Dmitry is right: as an oxidizer, $\ce{H2O2}$ will probably do little to help.

Community
  • 1
hBy2Py
  • 17,319
  • 3
  • 64
  • 109
  • 1
    Hydrogen peroxide reacts with bleach to yield oxygen gas, so it would also be useful to eliminate the bleach. The problem isn't that it doesn't react, it's that how do you get rid of the excess hydrogen peroxide after you react the bleach away? H2O2 is probably worse for soil than oxidized vitamin C. – Curt F. Jul 23 '15 at 16:52
  • 2
    Sodium thiosulfate is used in aquarium chlorine removal. It's an alternative to ascorbic acid, and cheaper. In the quantities used in aquarium maintenance, it's safe for fish, and certainly for the much hardier bacteria and protists. – DrMoishe Pippik Jul 23 '15 at 23:13
0

What are you afraid of exactly? The quantity of bleach remaining after the rinse is certainly miniscule, and it will exponentially drop each time you refill the barrels with rain water.

If you're really concerned (which IMO you shouldn't be), you can refrain from using the water you collect the first time. Also, the bleach is designed to react with organic compounds (dirt), so rinsing the barrels with dirty water will make the remaining bleach react with it.

Hydrogen Peroxide is an oxydizer just as the bleach, so it will not help.

Dmitry Grigoryev
  • 457
  • 5
  • 18
  • Indeed, when washing glassware, most chemists will rinse repeatedly as you indicate. – Geoff Hutchison Jul 23 '15 at 15:40
  • Hydrogen peroxide reacts with bleach to yield oxygen gas, so it would also be useful to eliminate the bleach. The problem isn't that it doesn't react, it's that how do you get rid of the excess hydrogen peroxide after you react the bleach away? H2O2 is probably worse for soil than oxidized vitamin C. – Curt F. Jul 23 '15 at 16:52
  • 2
    @CurtF. Hydrogen peroxide is a common (minor) side product in oxidation of organics by aerobic organisms, and they learned to deal with small amounts of it rather efficiently. – permeakra Jul 24 '15 at 08:43