Catalytic carbon not removing iron

Users who are viewing this thread

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
So my iron woes continue. Last week I plumbed in a new 1.5 cuft catalytic carbon system to remove oxidized (ferric) iron. So my system now looks like this:

Well ---> Soda ash injection ---> peroxide injection ---> contact tank ---> Katalox Light filter ---> catalytic carbon filter ---> softener

I made monitoring ports after each step using boiler drain valves, and I have been monitoring the water closely. I'm especially concerned about the quality of the water as it enters the softener, as I don't want to foul the softener resin. Unfortunately, at the moment, the water going into the softener is pretty bad. It still has over 5 ppm of iron, pretty much all of which seems to be ferric. The water is the color of tea.

So why isn't my new catalytic carbon filter removing the ferric iron? I thought cat. carbon was the media of choice after peroxide injection? I bought it because the water coming out of the KL was horrible. Unfortunately, it is STILL horrible even after coming through my new cat. carbon filter!

I used clear plastic tubing for the backwash drain line, so I can see the condition of the backwash water, and it looks relatively clear... further indicating that the filter isn't doing much of anything because very little rust is going to drain. The size of the filter is compatible with our flow rates, so I don't think sizing is the problem. It seems to me there are two possible reasons:

1) I was wrong, and cat. carbon is NOT the best media for removing oxidized iron. If this is true, then what is the best media for this?
2) The unit isn't working properly. It has a Fleck 5600SXT head, which looks straightforward and seems to be operating fine, as far as I can tell. The only thing I can think is that the riser tube isn't seated properly in the head, but I did check for this when I put it together and it seemed to be snug, as far as I can tell...

Frustrated...

... If anyone has any suggestions, I'd sure appreciate it!
 

Reach4

Well-Known Member
Messages
38,797
Reaction score
4,412
Points
113
Location
IL
Man, you have quite the system.

I think the tests test for ferrous iron. Filtering ferric iron is more mechanical than catalytic,pretty much any filter should filter ferric iron (rust) particles. So I think you have remaining ferrous iron. To give more remaining oxygen to the water that the catalytic carbon deals with, I think I would try cranking up the peroxide.

I think your KL filter takes the water from 20 ppm iron to 5 ppm.
 

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
Hi Reach4 - I always value your input!

I think it is definitely ferric because I can observe what happens when I turn the stenner pump for the peroxide on and off. With the peroxide pump off, the water coming out of the carbon filter will be only slightly orange in color. With the peroxide pump on, the water coming out of the carbon filter will be darker orange. In either case, the amount is over 5 ppm, which I know because I have been testing it with an iron test kit. The kit tests for total combined iron, both 'ous and 'ic.

It appears that with the peroxide pump OFF, the KL media doesn't have enough oxidizing power to convert all the ferrous iron to ferric.

With the peroxide pump ON, all of the ferrous iron is converted to ferric, but then the KL media and carbon aren't able to mechanically filter it all.

Talk about being between a rock and a hard place. In my case, both the rock and the hard place are made of iron, LOL!

I just wish I knew why the carbon filter isn't removing much ferric iron. I thought catalytic carbon was supposed to be good at that?
 

Reach4

Well-Known Member
Messages
38,797
Reaction score
4,412
Points
113
Location
IL
I just wish I knew why the carbon filter isn't removing much ferric iron. I thought catalytic carbon was supposed to be good at that?
I had not heard that catalytic carbon was especially good at removing particles compared to other media. I did think that any backwashing filter would take out such solids if the particles were big enough. I was thinking that the ferric iron that the catalytic action produce would be big enough to filter out easily. I may have been mistaken on that.

If you tap off your orange water into a glass, how long does for much orange to settle out? If much drops soon, I would be thinking of a Lakos TwistIIclean followed by a 4.5x20 Big Blue. If not much drops out, I would be thinking of 2 or 3 Big Blues, with maybe the first having no element.
 
Last edited:

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
It begins to settle out immediately, but really requires several hours for any serious settling to occur. If I leave a bucket of water overnight, it's pretty clear by the following morning. I actually do have a 20" cartridge filter that is very similar to the Big Blue. I didn't think I'd ever need it again with the new backwashing tanks. But maybe I should plumb it back in and get a few fresh cartridges. Of course, I remember how much that thing reduces the flow, but maybe it should go back into service at least temporarily until I figure out a better solution.

I guess I got the idea that catalytic carbon would filter ferric iron from looking what filter media is used by companies that sell commercial peroxide systems. For instance, the Fusion OXi-Gen system from US Water Systems is a peroxide injector and catalytic carbon tank. Although (and I had forgotten this until I just looked now), that kit also includes a cartridge filter! They refer to it as a "pre-filter," which would indicate to me that it is designed to go before the AC, and not after, as I would have assumed it would go.

So I guess I'll put the 20" cartridge filter back in service and see what happens. The only upside to all of this is that my plumbing skills are improving - I'm getting pretty good at sweating copper pipe! ;)
 

Reach4

Well-Known Member
Messages
38,797
Reaction score
4,412
Points
113
Location
IL
That is interesting.

If you filled glasses of water from each sample drain, I wonder which would have the most stuff to settle.
 

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
Yeah, that might be an interesting experiment. If I can find 3 mason jars I'll give it a try. I don't want to use kitchen glasses because once the rust settles it is hard to remove, even from glass surfaces. The wife will yell if I destroy 3 glasses. ;-)

One thing is for sure, it's bad at all stages, until the very end, when the softener finally gets the water in decent shape (although we're still getting about 1 ppm even after the softener). Right after shocking it with the soda ash and peroxide, it's REALLY bad. Amazingly bad, in fact. Then, after going through the KL filter, it gets substantially better, though still cloudy with rust. Then after the AC filter, there is barely any change at all.

What's really funny is to see the color of the backwash water in the clear plastic drain line for the KL. I'll have to take a picture. It is so dark brown that it looks like chocolate. Not milk chocolate either - we're talkin' high grade 90% imported gourmet cocoa!
 

Reach4

Well-Known Member
Messages
38,797
Reaction score
4,412
Points
113
Location
IL
eah, that might be an interesting experiment. If I can find 3 mason jars I'll give it a try. I don't want to use kitchen glasses because once the rust settles it is hard to remove, even from glass surfaces.
Check with friends who are feeding a toddler baby food for glass jars.
 

ditttohead

Water systems designer, R&D
Messages
6,088
Reaction score
455
Points
83
Location
Ontario California
Just a thought. While GAC can be used for ferric iron reduction, it is not what it is intended for. GAC has no real specification for sediment reduction which is what ferric iron really is. If the iron has not turned to ferric completely before it hits the GAC, it will pass through the GAC. A larger contact tank would be recommended or you could even remove a little GAC and add some Clinptilolite which acts as a 3-5 micron sediment filter. Without proper and adequate contact time your results will vary.
What size is your contact tank? A simple static inline mixer after your chemical injection may also be of some benefit.
 

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
Thanks Dittohead - the contact tank is actually an old 2 cuft calcite neutralizer, which I emptied all the calcite out of. Then it goes on to the pressure tank, which is a nominal 40 gallons, but I'm not sure what it is in reality because of the bladder/air. Regarding the clinptilolite, any preference between Filter Ag and Chemsorb? Or are they pretty much the same thing? And would I have to change any settings on the Fleck 5600SXT head? There is a hand-written sticker on the drain line which says 5 gpm, which I assume is what it's set to backwash at for carbon. But the clinptilolite is heavier, right? And would need greater backwash flow?
 

ditttohead

Water systems designer, R&D
Messages
6,088
Reaction score
455
Points
83
Location
Ontario California
The 2 cu. ft tank would be approximately 20 gallons, the 40 gallon pressure tank would not really count toward contact time since it shares the same inlet/outlet, very little contact time would be calculated. There are companies that make smaller contact tanks that simulate larger tanks, nothing beats an actual large contact tank. As you can see from the test, water needs time to oxidize out the iron completely. Or you can try completely overdosing with chlorine injection, not really a good solution.

A larger contact tank, a static mixer, and you should see much better results.

DSCF3697.JPG
 

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
Interesting - so I did a simple test... I poured a glass of raw water and then squirted some peroxide into it. The effect was immediate - the color of the water changed instantly from clear to orange. Wouldn't this indicate that contact time is sufficient? I do think I remember reading that peroxide reacts with iron more quickly than does chlorine, so maybe contact time is a bigger issue when injecting chlorine?
 

ditttohead

Water systems designer, R&D
Messages
6,088
Reaction score
455
Points
83
Location
Ontario California
Contact time and quantity... Squirting some peroxide into a jar would be a huge amount. You certainly would not want to drink it. Consider that a gallon of bleach has approximately 65,000 ppm, you typically want a residual of 1 ppm, so a gallon of standard household dilution bleach could treat 65,000 gallons of water that was iron free. In order for smaller amounts of oxidants to work, you need contact time, or smaller contact tanks and overdose. This is one reason the pellet systems work so well, they typically massively overdose. But since carbon tanks have such a huge capacity for chlorine reduction, it is easily reduced back down to safe levels.
 

diggity

Member
Messages
71
Reaction score
0
Points
6
Location
Central MA
Ahh OK, gotcha, thanks. Makes sense.
I didn't have the time to make any big changes to the system last night, but I did increase the feed rate for the peroxide. I'll check it later after everyone has taken showers and enough water has flushed through the system and see if that helped.

Thanks!
 

Mikey

Aspiring Old Fart, EE, computer & networking geek
Messages
3,024
Reaction score
17
Points
38
Location
Hansville, Washington
The more contact time, the more iron reduction, and the more likely the ferric residue will precipitate out. Also, the typical system injects the chlorine after the pressure tank, while the pump is running, so it's highly concentrated and poorly mixed by the time it reaches the contact tank. With a 125 gallon contact tank, I still filter out a lot of ferric iron with a spun filter before going into the carbon tank. I'm planning on adding a purpose-built "swirly" retention tank (http://www.apwinc.com/retention_tank.html) before the pressure tank and injecting the chlorine prior to the swirly tank, while retaining the large tank downstream, in hopes of achieving better mixing and more complete precipitation.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks