Date: Sat, 28 Jul 2001 11:09:20 -0400
Reply-To: 72510.1173@COMPUSERVE.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Helen Fahy <72510.1173@COMPUSERVE.COM>
Subject: Re: Safe way to clean Westy water tank?
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> My water tank is pretty slimy (haven't used in
> awhile) and I'm looking for something to clean
> it with that won't poison me after I refill it.
> Any suggestions?
Actually there is no safe way to do this. If you do not feel comfortable
doing this, then do not.
For this type of disinfection, maintaining the chlorine level at 1000 ppm
for 20-30 minutes will kill everything in the tank, sterilizing it. To get
to this level with our 10 gallon tank and using household bleach
(5.25%)which is 52500 ppm, you need to add approximately 24.5 oz of bleach,
about 3 cups, to the tank and fill the tank.
{Conc of bleach * oz of bleach} + {conc of bleach in fresh water * (oz of
fresh water - oz of bleach)} = {Final conc * total volume}
{52500 ppmCL * (X oz)} + {0 ppm CL * (1280 oz - X oz)} = {1000 ppm CL
* 1280 oz}
Solve for X which is oz of bleach. In this case 24.38 oz of bleach
We run some of this solution through the pump to sterilize the pump and
piping to the sink, a minute or so. Then we drive around for the 20 to 30
minutes. The contact time of the chlorine mixture with all surfaces is
CRITICAL. Do not skimp on this time! It is equally important to flush the
entire system with a large quantity of known clean water, as chlorine is
corrosive and if left in the tank or pump will do damage at these high
concentrations. Do not forget to flush the pump and the piping to the sink.
After many of these treatments you may damage the pump, I do not know if the
pump materials are chlorine resistant. But it is cheap as compared to a
ruined trip and a trip to the hospital.
If you have a lot of green growies, flush them out as best you can.
Chlorine when combined with organic material can make trihalomethanes, which
are known carcinogens. If you can not flush these out, do not worry.
Remember you are not going to drink this stuff. This is just to kill
everything in the tank. You are going to flush the bejeezus out of the tank
with clean water.
Be careful of your eyes and clothing and upholstery when adding the bleach
to the tank. I remove the top of the tank from inside the van to add the
bleach.
BTW 1mg/l is 1 ppm, so 1000 mg/l is 1000 ppm
This is some info on chlorine for disinfecion:
Reactivity of Chlorine Compounds
Chlorine was first discovered to be a disinfectant in 1787 and has been
universally accepted and utilized ever since. The reactivity of chlorine has
been well studied and general guide lines for its use are as follows:
Inorganics: Chlorine, used by itself, requires a concentration of 6 mg/L per
1.0 mg/L of inorganic at a pH of 8.5 -9.0. If used in conjunction with
permanganate this ratio will drop to below 1.0 mg/L per 1.0 mg/L of
inorganic but will require tight instrumentation controls.
Pathogens: At a pH of 4-5, chlorine is effective as a disinfectant when used
at a ratio of 1-3 mg/L per 0.5 mg/L pathogen and requires a residence time
of 45 - 60 minutes (12 time that for Ozone).
Pathogens: A 500 mg/L chlorine concentration will normally be effective
against vegetative bacteria. At this concentration, chlorine has limited
effect against viruses and is poorly effective against bacterial spores and
fungi (adverse effects on body chemistry/metabolism).
Pathogens: a 1000 mg/L chlorine concentration is effective against all
bacteria, viruses and fungi yet requires 25-30 minute residence time
(adverse effects on body chemistry/metabolism).
Organics: practical applications of chlorine, even at 1000 mg/L have little
effect on oxidizing organic material other than generating chlorinated
organics, hence chlorine is not recommended for this use.
Residual: A chlorine residual can be provided only after the demand for
chlorine by inorganic, bacteria and organics has been met.
Chlorine can be effective for oxidizing inorganics and bacteria when pH,
concentration and residence time are allowed for, but the chlorinated
organic by-products are inevitable and only some may be filtered out. For
agriculture applications, the important consideration for utilizing chlorine
compounds is the amount of chlorides that will end up being consumed by an
animal, the impact of the chlorinated organics on the animals' performance
and toxic residues absorbed into the tissues of the animal.. If excess
chlorides are produced, necessary steps should be taken to remove them as a
last step in a water treatment program.
