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Treating water with UV lamp

 
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clv101
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PostPosted: Sun Sep 04, 2016 11:01 am    Post subject: Treating water with UV lamp Reply with quote

Does anyone have any experience running a UV lamp to treat rainwater or water from a well or borehole? A system to treat a 21 litre per minute flow rate consumes 30W.

The kicker is that the lamp is meant to be on 24/7, so consumes 0.72 kWh a day - around 10p of grid electricity but a substantial chunk of winter photovoltaic output from an off-grid system.

Are there any UV treatment solutions that don't operate 24/7? It would be nice if the lamp were only used when the water was flowing!
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adam2
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PostPosted: Sun Sep 04, 2016 11:30 am    Post subject: Reply with quote

Units certainly used to be available, and you might find a secondhand or surplus item.

They were used in the restaurant or buffet cars of the older trains to purify water used for food preparation.
The restaurant/buffet water tank was filled from a drinking drinking water supply, but to guard against subsequent contamination, UV treatment was applied at the point of use.

24 volt DC operation and used an 8 watt lamp.

I think that I still have a supply of the replacement lamps, but no complete units.
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Last edited by adam2 on Sat Sep 10, 2016 8:35 pm; edited 2 times in total
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Little John



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PostPosted: Sun Sep 04, 2016 11:34 am    Post subject: Reply with quote

What about pump-purification on an as-and-when-consumed basis?
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Little John



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PostPosted: Sun Sep 04, 2016 11:37 am    Post subject: Reply with quote

https://www.engineeringforchange.org/ten-low-cost-ways-to-treat-water/
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clv101
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PostPosted: Sun Sep 04, 2016 11:50 am    Post subject: Reply with quote

Little John wrote:
What about pump-purification on an as-and-when-consumed basis?


Yeah. This kind of system seems to avoid the 24/7 power requirement:
http://www.silverlineuk.co.uk/categories/reverse-osmosis-pump-system-36
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adam2
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PostPosted: Sun Sep 04, 2016 12:16 pm    Post subject: Reply with quote

Be aware that reverse osmosis water purification requires significant energy, usually electricity, to force the water through the filter.
Some types need no pump, but these require a relatively high water pressure such as mains water.

Hand operated reverse osmosis water "makers" exist but they need a lot of effort to produce a limited volume of water. Only suitable for use in life rafts or other survival situations and not for regular household use.

Also be aware that reverse osmosis water treatment needs expensive and very high technology replacement parts on a regular basis.

UV water treatment needs only replacement lamps, these are affordable and store indefinitely.
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adam2
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PostPosted: Sat Sep 10, 2016 8:50 pm    Post subject: Reply with quote

With the rapidly falling cost of PV modules, it might be worth simply accepting the continuous 30 watt consumption of the UV light and installing extra PV capacity for this purpose.

In UK winter conditions we get about one hour of "peak sun equivalent" a day.
So to replace the continuous 30 watts used, an additional 720 watts of PV capacity is needed, or perhaps a bit more due to battery losses.
800W of PV can be purchased for about 400.

Do you have any detailed technical data on the system design ? Depending on the design and intended use, it MIGHT be acceptable to turn the UV lamp off at night in the winter.
Presuming that no water is to be used at night except for flushing WC. Fill a clean jug with a few liters of water during the day, in case drinking water is wanted in the night.

Or perhaps accept discontinuing UV water treatment when electricity is short, and chlorinate the water instead.

More info needed.
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clv101
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PostPosted: Sat Sep 10, 2016 9:16 pm    Post subject: Reply with quote

Yes, I agree with the 'high technology' of osmosis pumps. I think UV is the answer and as you say the PV capacity isn't a show stopper even for a 30W lamp.

I'm currently thinking the answer might lie in a lower power lamp of around 8W, limiting the flow rate to something more modest like 4 litres per minute and maintaining a sterile ~50l header tank downstream of the lamp.
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adam2
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PostPosted: Tue Apr 03, 2018 9:13 pm    Post subject: Reply with quote

I have some spare 8 watt UV germicidal lamps, POA, but no complete units.
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BritDownUnder



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PostPosted: Wed Apr 04, 2018 8:58 am    Post subject: Reply with quote

I don't have any experience of these but in Australia these systems are commonplace as very many houses have their own water supply or an unfiltered water supply - in other words the council/supplier says 'here is the water , but drink it at your own risk'. You can see a few horror stories on the internet about the standard of water in some outback communities.

For example a 10 watt 6 litre per minute system for A$270.
It even has a system to control the lamp if it gets too hot if you want to pay A$140 more.

A idea of the cost of replacement bulbs.
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fuzzy



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PostPosted: Wed Apr 04, 2018 10:44 am    Post subject: Reply with quote

Why not just use curved mirrors to concentrate sunlight on the water? You could aways have a sliding cover to reduce light in summer, though I would be suprised if it was possible to have too much light.
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adam2
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PostPosted: Wed Apr 04, 2018 11:00 am    Post subject: Reply with quote

Possibly a worthwhile improvisation in an emergency, but not at all suitable for regular household use.
We get days with no sun, in winter hours of potential sunlight are very short.
What is needed whilst times are normal, and perhaps also during the long emergency, is a simple and preferably automatic system that uses a lamp of known output and lifetime, and that reliably treats water by means of a known flow rate.

The only consumable is lamps, the 8 watt ones at least are affordable enough for a lifetime could be stockpiled.
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