Experiment in Filtering Tap Water

[Planeden]

. . . waste water is cleaner than the source tap water. . .

Yeah, I used RO for years before I made that connection. Assuming a RO/DI is useing a TFC membrane (CFC is before the carbon instead of after, less common configuration) supply water goes through the sediment filter which pulls stuff out then goes through the carbon filter which pulls more stuff out so when it goes to the RO membrane a lot of stuff has been removed, chlorine being one example (but note ammonia is not removed even by the RO membrane and DI resin).

to borrow and expression from victoly "WHHOOOSH". .

interesting. i would have thought they would have some of the water go through the filters and then have a bypass for other water that will be your waste water.

but i am going to go check my filtered water for amonia. i don't care if it has ammonia in it, because my tank is cycled and amonia gets eaten by some of the poop bugs pretty fast. so, its just a curiousity. i never really knew why people were so concerned about putting amonia into the tank during topoffs and water changes when your fish do it every day. i'm not going to dump a bottle of it in there, but really, the small amounts in our water are clearly munched fast enough.

[Planeden]

. . . i just thought some people with smaller systems may be interested in an alternative to driving to pick up water or installing a large system. using victoly's 3:1 ratio, and a typical cost of $200 for an RODI system compared to $40 for mine, it seems like it'll be at least a year before i will start losing money. . .

I hesitate to say how long it's been since I looked at the cost/benefit equation but it was an easy choice for me to go with RO. After reading this thread I am really curious though how well a DIY carbon and DI filter made with home supply parts would do with a house that has a water softner installed, it's something I never looked at. Considering the ease of getting DI and carbon cartridges online in bulk it could have a pretty favorable long term maintenance cost if the DI cartirdges last a lot longer when used in conjuction with a standard whole house water softner.

i think for most people, anyone if you go long term enough (assuming nothing ever breaks and you just replace media), eventually the RODI systems will pay for themselves.

i'm curious what the cost is because this filter system is more expensive, especially long term. and i'm posting this because the main point i got in discussing this filter was cost, followed by it's not as good, followed by "shut up and just do RODI". cost was the smallest factor in my decision. everything in this hobby is a luxery, i expect it to cost money, so i just altered my water based on my budget of what i'm willing to spend on it.

my main concerns were space/installation and waste water. for people living in apartments where the space and their ability to modify (and short term living conditions) are a factor, this could be an alternative. for people that can't use and care about the waste water, this is also an alternative. i'm not trying to convince anyone to give up RODI in favor of this. y'all are all grown, you do what you want .

note: i know many people have various ways to use the waste water. i've heard a lot of them. most of them just end up in make work for me. i don't water my yard currently, so using waste water to water something i don't water is still waste water. the washing machine, ice maker, toilets, and toothbrushes use a set amount of water, so getting the waste water to those appliances that are already plumbed, doesn't save water, it just adds labor. blah blah blah.

[victoly]

. . . waste water is cleaner than the source tap water. . .

Yeah, I used RO for years before I made that connection. Assuming a RO/DI is useing a TFC membrane (CFC is before the carbon instead of after, less common configuration) supply water goes through the sediment filter which pulls stuff out then goes through the carbon filter which pulls more stuff out so when it goes to the RO membrane a lot of stuff has been removed, chlorine being one example (but note ammonia is not removed even by the RO membrane and DI resin).

You say the bit about ammonia quite a bit, and unless there is something I am misunderstanding, ammonia has a net negative charge which makes it amenable to be removed by DI resin.

"The extent of removal by the RO membrane depends on pH. At pH 7.5 or lower, reverse osmosis will remove ammonia from 1.4 ppm-Cl monochloramine to less than 0.1 ppm ammonia. The DI resin then removes any residual ammonia to levels unimportant to an aquarist."

http://www.reefkeeping.com/issues/2003-11/rhf/feature/

[Timfish]

. . . You say the bit about ammonia quite a bit, and unless there is something I am misunderstanding, ammonia has a net negative charge which makes it amenable to be removed by DI resin. . .

You're quite right, DI will remove the ammonia that's missed by the RO filter. I was curious and I've made that mistake 7 times over the last several years, I'm surprised no one has caught it before.

. . . "The extent of removal by the RO membrane depends on pH. At pH 7.5 or lower,

reverse osmosis will remove ammonia from 1.4 ppm-Cl monochloramine to less than 0.1 ppm ammonia. The DI resin then removes any residual ammonia to levels unimportant to an aquarist."

http://www.reefkeeping.com/issues/2003-11/rhf/feature/

That may very well be. But I would be very surprised if anyone's tap water around here is anywhere close to 7.5 pH, mines above 8.8. Irregardless though of the supply's pH there are measurable amounts of ammonia in our RO. I tested three different RO's today using API. One from the Meridian development on 45 & 1826 was .25ppm. Bee Caves near the New World Theater was .5 ppm. My own from north central Austin tested 0.0 ppm which surprised me as I have seen it as high as 1.0 ppm ammonia.

[victoly]

So to add to your discussion of ammonia in tap, the way that chloramine is introduced into treated water is that a mixture of chlorine and ammonia gasses are mixed with the water. If they don't get that ratio correct, you can end up with excess ammonia. Depending on a few variables (how far from the water treatment plant, which water treatment plant, etc) you could very well get different ammonia concentrations depending on that mixture on any given day.

[Timfish]

Good example of an "Ideal reading" that doesn't always happen in the real world.

[Timfish]

Update?

[Planeden]

Not much to update, really. I've made 36 gal on filter 1 and 55 gal on filter 2. Just finished 20 gal of making water and the last bit was at TDS = 1 ppm. Since the filters get tired as they make water, I will probably get longer filter life if I made less at a time. I think next time I pull the filters out I'll be back to 0 TDS, but probably have to replace at least filter 1, and possibly filter 2 depending on how closely I watch the TDS out of filter 1.

At this point, my best guess is that I'll get about 50 gal out of filter 1 and 100 gal out of filter 2. So, three filters for each 100 gal. At roughly $20 a filter, that's $0.60 per gal. This is an early guess, but it's more expensive than I expected. I would have expected filter 2 to last at least 200 gal. At my current usage rate, this is $5.00 a month.

I find I'm in a cunundrum. Since I'm posting this, I'm wondering if I need to be trying to maximize my results by being very careful, or using it like I intend to to just get results for myself. If I can splice in a valve between the two filters I can check the TDS coming from there easily enough and maximize filter 2 life. Also, I can figure out how many gallons I can make at once before the filters need a break.

[Timfish]

If you used regular filter housings you should be able to find DI cartridges a lot cheaper than the ones you are getting which have both carbon and DI resin in a single unit. I would be looking at setting up three units in sequence. 1st one with a generic 5 micron carbon cartridge and the second two with DI. An interesting comparison would be to try 2 carbon and one DI.

[Planeden]

If you used regular filter housings you should be able to find DI cartridges a lot cheaper than the ones you are getting which have both carbon and DI resin in a single unit. I would be looking at setting up three units in sequence. 1st one with a generic 5 micron carbon cartridge and the second two with DI. An interesting comparison would be to try 2 carbon and one DI.

where were you when i was setting this one up . that is interesting. the filters i have are about 2 DI units to 1 carbon units. i'm not sure if they use that ratio because the carbon effectively lasts twice as long or how they came up with it. the flow rate prescribed for these is 2 cups/minute as ideal. i'm not sure if changing the volume of the canisters would affect the flow rate or not.

it would be an interesting experiment. and probably a good way to decrease costs. i don't make enough water though to run a multi-setup experiment. perhaps when i run out of my current filters. i would think that one could set it up buying a 3 stage RODI unit leaving off the RO membranes and filling the canisters with the deseired media. of course, this is me, who knows little to nothing about how RODI filters are set up. i just know they have 3+ canisters and a bunch of tubes. . of course, i may be able to just push the media out of my canisters and refill with bulk media.

from what i understand, i think it came from neon reefer, RCA does not use the RO unit to make their water, but just run it through the DI resin. perhaps they would be a good source to talk to about proportions of carbon to DI and flow rates. but, if they can sell it for $0.20 / gallon, it would seem that the cost is lower than mine. unless it is just a money losing service they provide to people knowing they will usually buy other stuff while they are there.

[Planeden]

I just finished another batch. Filter 1 went out at 50 gal. Filter 2 is still going ok at 90. Before this is over I plan to splice in valve between the two filters so i can check TDS into filter 2 more easily (frequently) and maybe increase the life.