to allow flow of 2 amp current in water for killing bacteria

[Debashish_kar]

I need a constant 2 amp current to flow in a water sample for killing of some harmful bacteria.
basically I am using a 12 volt voltage converter and wires to flow current.

what are more efficient way of passing current ????
will there be any harmful effect of doing this process??

 

[SLK001]

I'm not sure that 2 amps will kill all the bacteria. You should try something like clorine or ozone to sanitize your water.

 

[RobertFalbo]

I'm not sure that 2 amps will kill all the bacteria. You should try something like clorine or ozone to sanitize your water.

or UV radiation.


With 12 volts, to get 2 Amps, you'll need 6 ohms of resistance.

Pure Water being a bad conductor of electricity, you will need to put your electrodes very close together and have a large surface area.

You could add salt to your water and lower it's resistance.

 

[BradtheRad]

Electricity does not easily flow in plain fresh water. You need to add salt, acid, etc.

It will help if you raise the voltage so that you push more Amperes through the water.

Also consider subjecting the water to static high voltage, although it's questionable that it kills all bacteria.

 

[c_mitra]

I need a constant 2 amp current to flow in a water sample for killing of some harmful bacteria.??

Current in water is carried by ions; it does not kill bacteria. Where did you find such information?

If you pass current in water, there will be electrolysis taking place. Current is carried by electrons in metals and ions in water. The area where the electrode touches water, electrons need to transfer the charge to ions. That is called electrolysis.

There will be certainly some harmful effects because (unless you use platinum or gold as electrodes) the electrodes will get corroded and get into the water as metal ions. That will make the water toxic.

 

[betwixt]

We need more information. Is this a potable water supply to a house/village/city or are you talking about tiny laboratory samples?

Certainly, electrocuting bacteria is a non-starter unless the water is only one or two mL and you have non-corrosive electrodes.

If you are trying to sterilize flowing water, the best option for you is to use UV. You can get ready made low-power UV sterilizers for use in aquariums and ponds that will work from the 24W you have available. A UV tube has a life expectancy of about 12 months so it will need replacing about once a year. Small aquarium types are not idea for drinking water but only because of their plastic rather than stainless steel construction, they are just as effective at killing bacteria.

You other possible option is a chlorinator. Commercial systems use a mix of hydrochloric acid and sodium chlorite to produce chlorine dioxide gas which is then dissolved in the water (it is highly soluble) but you can do it by electrolysis of salt solution. Hydrolysis is far less efficient though. You use common salt dissolved in water and pass a current through it. Gas forms at both electrodes and some of it is chlorine which you then bubble through the water. This method is only used on large scale chlorinators such as swimming pools because it leaves residual chlorine (bad taste/odor) in the water.

Brian.

 

[Externet]

With no doubt, electrical current destroys like 99% of microorganisms in water in less than 1 second at less than 1 Ampere. Unrectified (AC) can be more effective. If isolation is of concern to avoid shocks, a transformer is good to use.

The simplest non-isolated brute force method is

120VAC---------------switch---------------light bulb-------------------contaminated water-------------------neutral

The amount of current goes with the size of the batch; and if for continuous flow use, the size of the pipe/flow has to be taken in account. For poor conductivity water, any cheap salt dosage in small quantity will favor the action. Avoid too much salts as you want the microorganisms to be more conductive than the water itself.

This method is not to produce water for ingestion as ruptured cell walls leak potentially poisonous chemicals from the now-dead cell internals.

Any cheap disposable electrodes work; copper, iron,... just replace them if the time of use corrodes them instead of longer lived expensive precious metals.

 

[c_mitra]

With no doubt, electrical current destroys like 99% of microorganisms in water in less than 1 second at less than 1 Ampere. Unrectified (AC) can be more effective..

I have grave doubt.

 

[RobertFalbo]

If you run 2 amps through a small diameter tube of water. you will get heating. Enough heat and the bacteria will cook to death. AC is going to reduce electrolysis.

If killing the bacteria comes from heating the water, then heat the water indirectly. Try the heater in a coffee maker.



To get some more clarity on this.
you need to talk current density.
Amps /square cm.

Amps alone is not valid. I could put a 100 mile long 1 meter wide plate on the coat of Europe and another on the east coat of America. Run two amps across the Atlantic ocean and not kill a thing.

 

[c_mitra]

If you run 2 amps through a small diameter tube of water. you will get heating. Enough heat and the bacteria will cook to death. AC is going to reduce electrolysis...

Some bacteria are tough; you need to boil the water for 5-10 mins to kill them. Some of them love the heat (found in hot springs). 50-60Hz AC will not reduce (much) electrolysis (the capacitance is not much at this freq).

 

[betwixt]

All of this ignores that only 12V is available (24W max). Given the conductivity of water, assuming it has no additives that would make it essentially useless afterwards, it would be virtually impossible to pass 2A constant current at 12V unless the electrodes are very large and almost touching.

Brian.

 

[c_mitra]

All of this ignores that only 12V is available (24W max). Given the conductivity of water, assuming it has no additives that would make it essentially useless afterwards, it would be virtually impossible to pass 2A constant current at 12V unless the electrodes are very large and almost touching..

Exactly. Pure water has 10^6 Ohm.cm specific resistance and two electrodes (1sq cm each) must be placed (few microns apart...) to pass 2A current...

Tap water (it depends) is about 100-1000 times more conductive (often reported as TDS). But still it does not help much...

 

[KlausST]

Hi,

With no doubt, electrical current destroys like 99% of microorganisms in water in less than 1 second at less than 1 Ampere.

I doubt this.

Microorganismas are very small. With small volume. You need to introduce enough energy in the volume of the microorganism to distroy it.

Therefore the ammount of water between the electrodes willl have a lot of influence on effectivity.

***
Another thought:
What is killing the microorganisms?
The current through the microorganisms? If so, then making the water more conductive by adding salt makes the water more conductive, but not the microorganisms. --> this means less current through the microorganisms.

It´s like a lot of parallel resistors. Let´s say 100 pieces of 10k resistors, and one fo them is the microorganism with lets say 1k.
Now lowering the resistance of the 10k to 2k....with a constant current of x Amperes ... result in less ampere in the 1k of the microorganism.

Klaus

 

[dick_freebird]

Things like free oxygen from electrolytic cracking
might be the active principle (same, more or less,
as ozonation or hydrogen peroxide).

But throwing a lot of current may also mean throwing
a lot of electrode material, if it's not inert (like graphite).
That could contaminate the sample. If it's supposed to
be potable afterwards you would want to do an assay
with this in mind after an "over the top" treatment.

I would recommend the UV approach. UV LEDs for this
are becoming available, UV bulbs are cheap (ish) and
will decline in price as LEDs take over, no chance of
introducing other "stuff" into the water and so on.

 

[c_mitra]

I would recommend the UV approach. UV LEDs for this are becoming available, UV bulbs are cheap (ish) and will decline in price as LEDs take over, no chance of introducing other "stuff" into the water and so on.

UV is absorbed by the microorganism, the DNA gets damaged and the organism dies (fails to reproduce).

Unless the UV gets absorbed by the bacteria, it will have no effect. We need lots of UV (perhaps about 100W lamp for a 1L/min) so that we have about 100 photons /bacteria to cause damage (90% killing rate)

UV LEDs are expensive.

UV Hg lamps are expensive too (choke and starter) and are not popular because of Hg. It will take time for the UV LEDs will come down in price to be useful for water treatment.

 

[betwixt]

We need lots of UV (perhaps about 100W lamp for a 1L/min)

Commercial sterilizers are relatively inexpensive and use Hg tubes. They can be wired like conventional fluorescent tubes with a starter and choke but most use electronic ballast these days. I have several here but even the small 40W one can irradiate 20L/min. The tube sits inside a quartz flask (a giant test tube!) to keep it dry and that sits inside a stainless steel tube where the water flows around the flask. The advantage of the steel tube is it has a mirror like internal surface that reflects back any lost UV light. Only a few days ago there was a contamination scare here, mains water was found to be contaminated with e-Coli but samples taken after the sterilizer were fine.

I'm sure with a little ingenuity one working from 12V can be found or built.

Brian.

 

[Externet]

Fellows: Either the original poster or someone else closed this; either he does not care any more or got his answer and does not care about acknowledging our effort and time if I understand the following :

 

[Externet]

But posting is still enabled. ¿?
Can some EDAboard manager explain ? I cannot. Perhaps am misinterpreting the above attachment...

 

[Debashish_kar]

With no doubt, electrical current destroys like 99% of microorganisms in water in less than 1 second at less than 1 Ampere. Unrectified (AC) can be more effective. If isolation is of concern to avoid shocks, a transformer is good to use.

The simplest non-isolated brute force method is

120VAC---------------switch---------------light bulb-------------------contaminated water-------------------neutral

The amount of current goes with the size of the batch; and if for continuous flow use, the size of the pipe/flow has to be taken in account. For poor conductivity water, any cheap salt dosage in small quantity will favor the action. Avoid too much salts as you want the microorganisms to be more conductive than the water itself.

This method is not to produce water for ingestion as ruptured cell walls leak potentially poisonous chemicals from the now-dead cell internals.

Any cheap disposable electrodes work; copper, iron,... just replace them if the time of use corrodes them instead of longer lived expensive precious metals.

how is it possible practically !!!!......using ac may be harmful!!! . what can we do instead to get 1amp of current

can I have more details

 

[FvM]

There's no indication that "current flow" itself has sterilizing effects. The known effects of "electrolyzed water" (see e.g. https://en.wikipedia.org/wiki/Electrolysed_water) are related to electrolytic formation of compounds like chlorine or hypochlorous acid when DC current passes water with sufficient salt content.

The problem is that you also find many pseudo scientific publications about electrical water treatment in the internet. It may be difficult in some cases to assess it.