Carbon Filter Fact/Fiction Questions

[daveedka]

I beg to differ on that point...I have worked in a groundwater remediation plant that treats 2 MGD (million gallons/day)for more than 10 years, I and I have personally seen GAC desorb organic compounds into an effluent stream, and I've seen it happen multiple times, I also conducted a pilot program where a mixed media filter with carbon as the final polishing media desorbed volatilte organics...the common factor in all of these cases was carbon that had been used beyond it's service life...I have the GC/MS reports to prove it...these cases, although rare, are common enough for it to be a concern...

So you are saying that in these cases you know for a fact that all of the organics in question had actually been Adsorbed, And there was no other source, And the Organics were then released from the Carbon? How is this determined (Weight is the only thing I can think of) Also how is this controlled so that you know the results are accurate?
absorbed material will be released, adsorbed material will not. Carbon that has reached the point of saturation may still mechanically filter materials to some small extent, and the later release them Via Wash out but the Adsorbed material will remain there until removed via some process such as you describe in the latter part of your post. The process to remove the adsorbed material largely depends on the material needing to be removed.

I would really like to see the studies that led to your conclusions, especially the controls, methods, and processes used to make those determinations. I heven't yet found anything that shows adsorbed material can be released from Carbon in Fish tank conditions, But if there is something with good science behind It I'd certainly like to see it. Every experiment I've seen to Date (I do this for a hobby not a living so I haven't read it all) supporting the idea that adsorbed materials will release back out. Has had far to many variables to allow for any Kind of accurate conclusion. On the other hand, the experiments that have shown it will not be released are almost always properly documented, contriolled, and can be reproduced
Dave

 

[liv2padl]

every research paper i've read on this "desorption" of organics by carbon say that only under conditions of extreme pH and/or can this happen. such extremes would immediately result in a total fish kill.

i've never seen/read any research that suggests carbon can desorb organic compounds under aquarium conditions. i'd like very much to see such research and if Mantas can list a few papers in this regard i'd be grateful.

 

[Mantas]

It is pretty much common knowledge in the environmental remediation industry that carbon will desorb. I'm just trying to tell you guy's something I've seen happen first hand. I've been Plant Manager at a contaminated groundwater treatment plant for ten years. We have a New York State certified laboratory on site using gas cromatography and mass spectrometer analysis analyzing our water under the EPA 601/602 and 624 test protocols. Our calibration is checked through a state certified duplication program which is mirrored through an in-house EPA 625 test protocol and external independent audits and NYSDEC and EPA audits and spot checks.
The most recent incident in question occurred in April 2004 when a routine, daily set of samples tested above the MDL (method detection limit) for the compound cis-1,2dicloroethane (.9 ug/l or more commonly ppb(parts per billion)) which is a degradation product of trichloethane and tetrachloroethylene which are common groudwater contaminants in many parts of the country. These form a DNAPL (Dense Non Aqueous Phase Liquid solution which can lay at the bottom of an aquifer until removed(by pumping, air sparging etc.) or until it infiltrates through a pourous susurface layer into a deeper aquifer. The sample described above was taken as a daily (grab) sample at the plant effluent sample tap and when analyzed revealed a cis level of 1.4ppb (.5ppb above the allowable level on my NY SPDE's (State Pollution Discharge Elimination forms). We analyzed a duplicate sample and came to the same result. At that time a full set of PC (Process Control) samples was ordered by the NYSDEC Officer that is in charge of my SPDE's region in NY (Region 1). We then analyzed the samples and found that the contamination and the effluent from carbon filter unit 1 (CFE-1). This sample revealed a cis level of 2.2 ug/l the CFM-1 (carbon filter middle) and CFI-1(carbon filter inlet) samples had an undectable cis level. The MDL being .2ug/l.
The carbon in question was at roughly the end of it's ASL(anticipated service life) so we did a carbon change (this involves the pumping of 36000 pounds of GAC into a tanker, deconning both vessels and then filling them with 18000 pounds of GAC apiece. After backwashing fines and tanking pre-service inlet and out samples the units were placed back on line at which time the comtaminants were no longer present.
Per New York State Environmental Law I am require to report any daily sample above our permit limit or out of permit parameters for more than 100 organic compounds, volatile organic compunds and simple water quality results (pH(monitored continuosly on chart recoreder), iron and manganese, temperature(monitored continuosly on chart recorder), turbidity, alkalinity, etc...On the permit reporting form there is an explanation section for any violation of the permit. With the attached lab results I submitted the following explanation, Carbon Desorption, thats it. Under action taken I offered the following remedy, Carbon Changed. End of story. In other words it is so common im my industry no further explanation is needed. As far as any papers etc. related to the topic, take the NJDEP Industrial Wastewater Treatment License Course where the topic is covered quite thoroughly.

 

[Mantas]

I just read my last post and I see that it may be taken as I'm trying to be a know it all and show someone else up. I apologize if it appears that way and I don't want to degrade into a shouting match like so many of these threads seem to degrade into. There is room for discussion on any topic and I have learned alot from various members for years before I ever decided to stick my toe in the water and post myself. The only point I was trying to get across, without sounding smarmy or condescending, is that if carbon desorption is possible in the instances that I've seen it happen, it may be possible in an aquarium environment. Granted the instances I've seen it happen are under difficult conditions and it happened specifically with VOC's (volatile organic compounds), they are still organic compounds that have done it. All I was really trying to do was let the guy who started the thread know to change his carbon on a semi frequent basis rather than let it go until one day it leads to a problem, no more no less.

 

[joylynn]

I actually am finding this thread refreshing and am quite happy I got an intelligent discussion going, rather than the name-calling matches that have been going on here lately I have learned a great deal about carbon and its uses, and downfalls as part of this conversation and I appreciate the experience behind the discussion that is going on. Mantas, I didn't take it as you coming off as a know-it-all at all, just explaining something that is commonplace to you but that the rest of us have virtually no first-hand experience with. Thanks for all the discussion!

 

[daveedka]

Mantas, I'm certainly not offended, But from all of the information you are giving, I cannot see how one could distingiush between the carbon reaching it's saturation point, and tha carbon actually releasing materials that it already adsorbed. I can certainly see organics getting through the carbon and triggering your tests, But I am Guessing there were still organics in the water going into that carbon, So how do we seperate Desorption from Saturation.
MY questions were sincere and my Desire to see some science behind it is sincere.
Casual observations and industry assumptions have been going on for years and Mean nothing to me. The reason I asked for science is because I have never seen any That support the common Claims. Just because everyone says it, doesn't make it true. People have been saying things in this hobby for years that aren't true, and They can all find books/ and probably training manuals somewhere that back up their Claims. Good science still refutes certain Claims. Any govenrment facility or organization (EPA) is rife with mis-information and rediculous claims. The EPA in particular is well know for being so far frrom reality they couldn't find it with a globe and a private jet. I have had to deal with them more than once in my industry, and if they have any Qulified scientists working for them they keep them well hidden.

I have heard this claim all my life and like many I believed it. I saw a very knowledgeable Hobbyist Stand up to this claim a few years ago and I started researching it. As of Yet no one has ever shown me one Bit of information that shows AC can desorb materials under normal fishtank conditions. The myth still stands and people still make the claims, but I've yet to see any proof.
I really would still like to see something of the sort. I'm very sincere when I say that.

dave

 

[liv2padl]

mantas ... great discussion and appreciated. from what you describe, it 'sounds' like carbon reaching its saturation point (no sites remaining upon which adsorption can take place) and thus 'allowing' DOC's to pass through the carbon without being adsorbed. if there's a means for this to be determined, it would really help to further this discussion.