Carbon Filter for Mighty-Mite RO/DI Unit

[skh]

I've been using a mighty-mite RO/DI system for the past 3 years and I really like it. The only thing is that the in-line carbon filter for "taste and odor reduction" keeps getting clogged after about 10 months of use even though all the other filters chug along with no problems.

 

So, is the carbon filter necessary? My tap water is only at ~20 TDS straight out of the tap and I have a sediment pre-filter before the RO membrane and the DI right after. Is it fine to run this as a 3-stage system without the initial carbon stage? I'm only using the water for the tank, I'm not drinking it.

[Phixion]

If the carbon statge is BETWEEN the sediment and membrane, then YES you need it! Sediment filters won't catch 100% of when the carbon filter usually finishes off. ANY particles that get to the membrane will quickly clog it and require you to prematurely need to get a new one. FAR more expensive than just replacing the carbon filter yearly. Figure $12 for a carbon filter verses $50 for a membrane...

[disaster999]

weird how the sediment filter isnt catching everything before it goes to the carbon. how many micron cotton filter are you using in the sediment filter?

[AZDesertRat]

You should be changing your filters at 6 month intervals.

The carbon needs to be after the prefilter and before the RO membrane. It is there to adsorb chlorine so it does not damage the membrane.\

I suspect you are using low end prefilters in high micron ratiings that are allowing particulates to pass through and clog the pores in the carbon rendering it useless.

This may have already lead to membrane damage, a TDS meter will tell you the whole story. Take TDS readings from tap water, RO only water and final RO/DI water to see how the systems is working. If the RO only is say 10% of the tap water TDS then the membrane is probably in need of replacement and is relying on the DI to do the job it should be performing.

Use low micron prefilters and carbons, 1 micron or less, and you will get better membrane performance and better overall system life. If sediment or particulates are a problem then you may want a pleated 0.2 micron prefilter which has 10x the surface area for better treatment, less pressure drop and longer life. It will also alow the carbon to do as it is intended and adsorb chlorine in its billions of tiny pores since they won't be clogged.

[skh]

Thanks everyone for the replies. The carbon filter was setup as the first stage, before the sediment filter, and this is is how it came to me from Air, Water, Ice. In other words, Tap --> Carbon --> Sediment --> RO --> DI. I don't know offhand the micron rating for the sediment filter but I'll check when I get home today. I'll also try to do the TDS measurements -- both tap water and right after the RO membrane -- and report back.

 

Anyway, the point about needing to remove chlorine prior to the RO stage seems like a good one -- I'll get a new filter ASAP. I've run about 5 gallons through using only the sediment filter --> RO --> DI, but I'll hold off using it again until I get the new filters.

[AZDesertRat]

Configure it with sediment-carbon block-membrane-DI in that order. If the carbon is granular instead of a block it is often wise to have a sediment filter after the carbon to trap carbon dust or fines as it degrades but this exposes the carbon to sediment, particulates and colloidal materials that will very quickly foul the billions of tiny pores that adsorb the chlorine and VOCs. I would make sure its a carbon block and put the prefilter in front personally so it protects the carbon from fouling, plsu carbon blocks last easily 10x longer than granular products, on the order or 300 (60 RO/DI and 240 waste)total gallons vs 3,000 (600 RO/DI and 2400 waste) total gallons per filter.

[skh]

Configure it with sediment-carbon block-membrane-DI in that order. If the carbon is granular instead of a block it is often wise to have a sediment filter after the carbon to trap carbon dust or fines as it degrades but this exposes the carbon to sediment, particulates and colloidal materials that will very quickly foul the billions of tiny pores that adsorb the chlorine and VOCs. I would make sure its a carbon block and put the prefilter in front personally so it protects the carbon from fouling, plsu carbon blocks last easily 10x longer than granular products, on the order or 300 (60 RO/DI and 240 waste)total gallons vs 3,000 (600 RO/DI and 2400 waste) total gallons per filter.

 

Okay, thanks. Here's the description of the filters used in the system. It looks like it's a GAC carbon filter, not a carbon block.

 

(1) In-line quick connect 5 micron coconut shell granular activated carbon (GAC)

Dimension: 10" x 2"

(2) 10", 5 Micron In line sediment filter.

 

Link: http://www.airwaterice.com/category/18.individual_filters/

[AZDesertRat]

Find a carbon block if you can. I'm sure someone has them available in the inline style like you need. If not you really should have two sediment filters for best carbon and membrane life, one before the GAC to protect it and one after to protect the membrane.

I found an inline carbon block filter here:

http://www.spectrapure.com/St_replac_p2.htm

It should give you longer life and not produce carbon dust like the GAC will so can be placed after a sediment prefilter and not need a post carbon sediment filter.

[skh]

Find a carbon block if you can. I'm sure someone has them available in the inline style like you need. If not you really should have two sediment filters for best carbon and membrane life, one before the GAC to protect it and one after to protect the membrane.

I found an inline carbon block filter here:

http://www.spectrapure.com/St_replac_p2.htm

It should give you longer life and not produce carbon dust like the GAC will so can be placed after a sediment prefilter and not need a post carbon sediment filter.

 

Thanks for the help ADR. One last question - if my municipal water system uses chloramine rather than chlorine, is it sufficient to use GAC or a carbon block, or do I really need to use catalytic carbon instead? I've had this system running for three years and am not aware that I've had any ammonia problems before and would like to avoid having to add an extra vertical filter housing to the system.

 

Edit: Here's an interesting discussion of chloramines in an RC thread that suggests that at least chloramines may not harm TFC RO membranes.

http://www.reefcentral.com/forums/showthread.php?t=200056

 

Edit #2: Also found this 2003 article about removing chloramines in reefkeeping magazine.

http://www.reefkeeping.com/issues/2003-11/...ature/index.php

 

Edit #3: The reefkeeping article suggests that a GAC or carbon block filter may be adequate to remove chloramines, but that the performance degrades significantly when the system pressure drops due to the carbon filter clogging (which is responsible for removing the chlorine in the chloramine compound), and that at this point chloramine is likely getting through in too large quantities even if the TDS is still reading 0.

[AZDesertRat]

A single carbon block is sufficient as long as it is preceded by a good low micron prefilter so it does not become fouled. Spectrapure uses a single 0.5 micron carbon block on all their premium systems and their research has shown this to be sufficient. I trust them more than about any other when it comes to RO/DI as they have been doing it for 25 years and the owner is a biochemist himself. The do more in house research and development than all the others combined and then some.

For chloramines what is most important is good DI resin to remove the ammonia portion not the carbon as many believe. Any carbon wil be effective at least for a time so thats why the good prefilter comes into play, the better the prefilter and carbon the longer both the carbon and the membrane last.

 

Notice in the articles you pointed out Charles and Spectrapure authored one and Randy Holmes Farley who is a big end user of Spectrapure products as am I authored the other. You will probably still find a lot of my threads on RO/DI still too as I was a member of Team RC and a resident expert before they decided they didn't like me any more when I pointed out one of their Sponsors was making false claims they could not back up with evidence. I guess the amlighty dolar won out and they banned me, I look at it as a loss for them personally plus I am much happier here and other forums which are less censored or restricted as far as free speech.

[skh]

A single carbon block is sufficient as long as it is preceded by a good low micron prefilter so it does not become fouled. Spectrapure uses a single 0.5 micron carbon block on all their premium systems and their research has shown this to be sufficient. I trust them more than about any other when it comes to RO/DI as they have been doing it for 25 years and the owner is a biochemist himself. The do more in house research and development than all the others combined and then some.

For chloramines what is most important is good DI resin to remove the ammonia portion not the carbon as many believe. Any carbon wil be effective at least for a time so thats why the good prefilter comes into play, the better the prefilter and carbon the longer both the carbon and the membrane last.

 

Notice in the articles you pointed out Charles and Spectrapure authored one and Randy Holmes Farley who is a big end user of Spectrapure products as am I authored the other. You will probably still find a lot of my threads on RO/DI still too as I was a member of Team RC and a resident expert before they decided they didn't like me any more when I pointed out one of their Sponsors was making false claims they could not back up with evidence. I guess the amlighty dolar won out and they banned me, I look at it as a loss for them personally plus I am much happier here and other forums which are less censored or restricted as far as free speech.

 

Cool, thanks again. Yes, I came across your posts on RC shortly after posting this. Sorry about the fallout at RC but very glad to have you here on NR.

[skh]

Well, my new filters just arrived and I've hooked them up. I took some TDS readings to see how things were faring and I found some surprising results.

 

Tap: 125 ppm

After sediment and GAC filters: 176 ppm

After RO membrane: 69 ppm

After DI: 0 ppm

 

I was shocked by the three first readings. The 125 ppm out of the tap is way higher than the usual ~30 ppm I've measured in the past and I assume that's because we're in the rainy season here and the runoff has increased turbidity and dissolved solids. The 176 ppm reading after the sediment and GAC is also very surprising but I assume that has to do with the breakdown of the chloramine. The 69 ppm after the membrane is also way higher than I had thought it would be. Although it's disappointing to get such high readings from the RO membrane, it works well enough during most of the year when the tap water is only about 30 ppm.

[Scott Riemer]

For all you've invested in the system, just a thought, but you could have a full size Spectrapure system. Seems like you're going to quickly exhaust your DI.

[skh]

For all you've invested in the system, just a thought, but you could have a full size Spectrapure system. Seems like you're going to quickly exhaust your DI.

 

True. But I've gotten 2 1/2 years out of this setup with just two carbon cartridge changes, which I'm pretty happy with. A Spectrapure system would probably be more economical in the long run but my water needs -- 5-7 gallons per week -- are low enough that I don't feel too bad about not spending more money up front for a nicer system.

[AZDesertRat]

Prefilters and carbons do absolutely nothing for TDS, in fact granular products add TDS as you just found out. A carbon block will no tadd TDS but it won't reduce it either, not any significant amount anyway. They are there solely to protect the RO membrane which in your case looks like has failed. You are at 45% rejection and it should be 96-98% rejection. You need to retest everything minus the TDS after the carbon as it tells you nothing. If its still high after the membrane it needs replacing.