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UV Disinfection for a Cottage |
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Written by Mike
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Grant from Scarborough Writes:
Thinking of buying a system for the cottage. Have you ever heard of Rainfresh? I can get a good deal on Prod. # 62-1006-4 at Cantire through my buddy.
Anyways, when considering a UV for the cottage with infrequent use, what are the things I should be mindful of when purchasing?
I know the ballast seems to be a big issue with all manufacturers, and may be it is better to go with a proven brand like Sterilite. The other problem is the the UV dose info is absent on the Cantire website.
Rainfresh is a cheapy cheap system. Usually those systems give you a dosage of 30 mg/cm2 at the beginning of lamp life and at near perfect UVT. Your lake water will have nowhere near perfect UVT and it won't be long before your lamp outputs stabilize and start dropping.
Most ballasts are similar for just about every U.V. system. They do not like being turned on and off frequently, but it's ok on a regular basis I.E. turning the system off when leaving the cottage and turning it back on when using the cottage again. Just make sure that you give the unit sufficient time to warm up, say an hour, before using the water.
The other thing you may want to consider, if the lake water is hard, is to leave a tap trickling when you plan to not use the system for more than a few hours. This will help prevent scale build-up, which you will have NO idea is happening because that system does not have any alarm features.
Because the system is not monitored and the dosage will be spotty, my recommendation would be to use this system for washing, showering and toilet flushing only, and to a safe bottled water supply with you for drinking and cooking.
Hope that helps.
Thanks for the below email. I have copied your other email, and some of my family members to let them know what I am planning.
I looked at the Rainfresh website, and they claim 40 mg/cm2. Interesting comment on what you think the dose will be. Could they be using cheap lamps? I gather the way the ballast is set up would also affect the lamp output. Any idea where I could get more info on this company?
I measured my water quality at the cottage from June - October last year. Here is a synopsis of the results for raw lake water:
-pH: 7.0 ± 0.2
-Hardness: 35 - 50 mg/L CaCO3
-Conductivity: 78.64 microsiemens
-TDS: 50.96 mg/L
-ORP: 154 mV
-UVT: 79.7 %
-Turbidity: 0.76 NTU
-Iron: 0 mg/L
So there is some stuff in the water, but I do not think it is unreasonable to treat. Colour is also an issue, though I did not have the tools to measure it. The water quality tends to be the same in the summer despite the temps being higher and activity in the lake by the cottagers. In September turbidity was a little bit higher than average (0.9), while in October it was lower (0.5).
My plan is to have pre-filtration with two (2) 10" cartridge filters. First will be a 20 micron, followed by a 5 micron GAC filter, and then the UV.
One idea I am playing with is to plumb a garden timer into the system. The purpose of this is three fold:
-provide a water connection to service the property (i.e. Spray boat down, wash windows, water flowers, etc.), which we do not have at present;
-while we are away from the cottage for long stretches, dump the static water in the filters and UV to prevent fouling;
-in conjunction with the last comment, cycle the pump on/off to prevent corrosion build-up in the cast iron pump head.
The timer would be set for once a day, and drain water from the system for 1-2 minutes when the cottage is not being used. It would not be used when the cottage is occupied.
Thus, the water system would be safe whoever used it next. My preference would be that the UV makes the water safe enough to drink, but perhaps we could use one of those tap filters or an under the sink RO system just in case. Ideally, we will not have to pre-boil water for cooking or cleaning dishes.
I am seriously about doing this because we have Anara now, and do not want her to get sick from any possible exposure. For example, if we bath her while up there.
Any experience or expertise you can offer is appreciated.
The only way that you can be sure to have a primary disinfection system that works for drinking water is to have a primary disinfection system that guarantee's a minimum dosage of 40 mg/cm2 and alarms and shuts off if it doesn't. This means having a system that has a flow restrictor and can monitor both the lamp output and UVT to get the three things needed to calculate dose:
-flow (inferred maximum by flow restrictor) -Lamp energy output -UVT
This means you'll want to go with a system that has an NSF 55 class A rating (or similar third party specifications). We're talking either U.V. Pure or that Steralite system.
You have very low hardness which is typical for surface water and that is a good thing. Your UVT is also low which is typical for shallow lakes as well. Your GAC filter will probably (but may not) raise the UVT - A Hallett upstream is good down to a UVT of 75% (I don't know the specs on the Steralite). You could also buy an upstream 10-50 - only 10 GPM max but it's good for a UVT down to 50%.
If I were you, I would look at purchasing the Hallett Upstream. It is not NSF 55a but built to the same specs and third party validated (saves significant money). It has a built in temperature based purge valve which would keep water moving when you are not using the system. It will also tell you exactly what your lamp outputs and UVT are right on the screen, which will help you determine when your GAC filter is starting to lose effectiveness and needs to be changed (or perhaps spring or falltime lake turnover too!).
I assume that you have run raw water through your plumbing for years - U.V. does not provide for secondary disinfection so I would shock your plumbing with chlorine before using it to kill any biofilm that may have formed on the inside surfaces of the plumbing. As chlorine is only a surface disinfectant, I would look at shocking your plumbing on a regular basis (perhaps once a month) in the absence of regular bacti testing that involves indicator organisms like background and Heterotrophic plate counts.
I think a proper dosage is very important in your case. Surface water can contain giardia and crypto cysts. Your filters will not remove cysts (you need a 1 micron absolute for that). Coliform bacteria is easily killed by a small U.V. dose, but crypto needs a higher one. You probably don't want Anara splashing around in water that may contain cysts (look up the North Battleford, SK Incident).
Yea I know, I'm expensive.
Let me know if you have any other questions.
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