Possibility of using a UVC LED to disinfect water?

[RaGun]

Hey everyone,

I recently came across UVC leds and was wondering if they could be used to disinfect water in a simple way.

If I got a bucket with 5 litres of water in it, stuck a 50mW radiant flux UVC led (like this) on the lid and run it for 1 minute would that be enough time and power to disinfect all the water? Would there be any difference in effectiveness if the interior surface of the bucket was reflective so the light would reflect more?

Thanks for reading.

 

[BillTre]

That should work, given the proper dose of UV.
If you try this, you should ensure to protect yourself (and especially your eyes) from UV exposure.

Would there be any difference in effectiveness if the interior surface of the bucket was reflective so the light would reflect more?

That would increase the effectiveness of the UV because the UV intensity would be increased by reflecting unabsorbed UV.

There are many products available that do this.
I am familiar UV illumination devices in recirculating aquaculture water systems, where they are used for disease control.

The dose for enough UV for these devices to achieve killing of organisms is based on:

• the intenssity and wavelength of UV produced
• the exposure time of the water in the device being exposed to the UV (volume of illuminated water/rate of flow)
• the clarity of the water
• the suspectability of the particular organism to the wavelengths of UV being produced

The same parameters could be applied to a bucket of non-moving water.
See the effectiveness section in this wikipedia entry.

 

[RaGun]

given the proper dose of UV.

This is the important question for me.

UV dose µWs/cm² = UV intensity µW/cm² x Exposure time (seconds)

The LED site mentions the radiant output of 50mW but doesn't mention the area so I'm not sure what to put in the UV intensity section of the above equation.

Would it be the internal area of the container?
A 18cm diameter, 20cm height container can hold 5 litres and it's area is 1384cm².

So would it be (50000µW / 1384) x 60 seconds = a UV dose of 2167µWs/cm²
This particular equation is for a 1 meter distance so intensity on a 5 litre container that is only 20cm high should be much higher. This also doesn't take into account the light reflecting internally in a shiny container.

If my working out is correct this is already getting close to the minimum dose to reduce cryptosporidium by 90% but I can't find the amount for giardia and virus deactivation dosages.

 

[BillTre]

You are entering into an engineering project with a bit of complexity.

The intensity will be determined by the efficiency of the electrical current producing the light from your light source. This will vary depending on the details of what you are using. With a manufactured product (such as an aquacultural UV sterilizing unit) using a designated light source, you can get the information from the manufacturer. You might be able to get this information for the LED you have from its manufacturer.

Alternatively you could measure the UV output directly which would also take into account the amount of reflected light your container could provide. Otherwise you could try to figure that out or assume it does not happen and end up with a higher UV dose, which would improve safety for human consumption.

A very important consideration in effectiveness of dose is the water clarity. For this reason, in water recirculation systems, particle filtration is always placed upstream of the UV. If your water is not clear, you should filter it first.

Also if you are putting the UV through any glass, you should use quartz glass which passes UV more effectively than other kinds of (affordable) glass. This is another factor that the engineers build into the effectiveness calculations of particular manufactured products.

An additional factor is the age of the light source. Traditional UV fluorescent tube age over a period of months and end up with a reduced UV output. For fluorescent bulbs, this information is provided by the bulb manufacturer and is taken into account by only using the bulbs for a certain time period and sizing the UV dose for the aged output of the bulb. Does this apply to LEDs? I don't know, but it would not surprise me if LED output reduces with long term use.

edit:
Here is a pdf with doses for some of the organisms you mentioned.
It is my understanding that Giardia can removed by filtration by campers (or boiling).
If I were doing this for water for human consumption, I would use a higher than 90% inactivation rate in determining my UV dose.

 

[Laroxe]

Its described in detail on wikipedia, if I'm allowed to use such language. Its the short wavelength UV light that is most effective (UV-C), in clean relatively shallow water, sunlight will often do the job but any solid organic mater needs to be removed so filtration always comes first. There are filters that remove most micro-organisms but these often require significant pressure to force the water through.
https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradiation