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Water disinfection: looking beyond chlorine

  • Water disinfection: looking beyond chlorine

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Ever since the discovery of microscopic life, man has always been weary of bacteria in water.

And rightfully so.

Microorganisms in water are associated with a number of severe to deadly infections such as cholera, dysentry and typhoid.

Since many water microrganisms succumb at a temperature of around 80 degrees celcius, boiling has been employed in water disinfection in many low income households.

However, boiling water might compete with other domestic needs for fuel such as cooking.

It is for this reason that alternative water disinfection methods are essential and in this regard, chlorine rarely disappoints.

Residual chlorine

Chlorination of water is not only a sure way of getting rid of a spectrum of microorganisms but also impedes their build up.

This is because chlorine lingers in water long after being introduced into it…

An added advantage referred to as ‘residual chlorine‘.

Picture a water treatment plant which suspects a certain threshold of microorganisms in municipal water.

Common sense would dictate introducing just sufficient chlorine to wipe out all the bacteria but this isn’t usually the case.

Instead, a water treatment expert would introduce a dosage slightly higher than the threshold value for the excess chlorine to be left lingering in the water.

This would tackle any germs that could gain entry through pipe leakages.

This is the principle behind residual chlorine…

A reserve armoury ready to tackle any extra microbial threat to our water.

Because chlorine exists as a radical (or electron scavenging species) in water, it rapidly degrades bacterial coatings rendering them harmless.

But this disinfection tactic is not just confined to chlorine.

Solar disinfection

Ever been thirsty and out of drinking options?

Ever been forced to rely on drinking water from suspect sources because you are out on a journey or just can’t access treated water?

Well, just collect the ‘suspect’ water in a transparent plastic container after filtering off the the suspended solids then allow it to sit in the sunlight for a while.

Over time, the bacterial load in the water might be reduced to a level that is safe for drinking.

Sunlight contains ultraviolet rays which have the ability to ‘split’ water momentarily forming radical species much in the same way chlorine behaves.

These radical species interact with bacteria destroying them and rendering them harmless.

But a word of caution…

Ensure that the water is in a transparent bottle for sunlight to penetrate…

Also try using reasonably safe water such as rain or river water (from a source far from industrial activity).

Using sewage for this purpose might be very risky because of its high level of contanimants and microbial load.

This same principle is used in UV disinfection where specialized lights optimized to target microrganisms are passed through water in more sophisticated water treatment plants.

UV disinfection might also be accelerated by the use of UV active metallic oxides such as those of titanium.

In this case, these oxides are ‘activated’ to kill bacteria on contact thereby improving filter efficiency.

But besides titanium, another precious metal has been tested and tried efficiently in water disinfection applications.


Silver teems with many surface electrons making it an excellent conductor of heat and electricity.

But these same electrons could be used to target bacteria by destroying their coating upon contact.

Though metallic silver might work just as well, it’s high costs are very prohibitive.

Also, it might not be as efficient enough to completely remove all microbes from water because of inadequate surface area for contact.

But what happens when the block of silver is reduced into many nanometre sized particles?

The increase in surface area to volume ratio guarantees more efficiency in disinfection due to bacterial contact.

Silver nanoparticles offer a couple of advantages compared to other water disinfection techniques:

First, they are minute in size requiring a very little amount of silver.

Secondly, they could be incorporated into traditional water ceramic filters guaranteeing disinfection as filtration of suspended solids is taking place.

Lastly, they can easily be manufactured from a minute amount of silver salts (available in lab tech shops) by reacting them with plant extracts.

However, a major disadvantage with nanosilver in water treatment is its lack of residual disinfection after initial bacterial removal.

In conclusion

Though chlorination holds many useful advantages in water disinfection, there is need for more R&D on alternative water treatment strategies.

Microorganisms must be stopped from polluting our drinking water.

We have an opportunity to act on behalf of ourselves but most importantly our children.

Originally posted on John Mmbaga's blog

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