Activated Carbon - Contact Times

[ivanhoe374]

I am currently looking at a project of treating 140m3/hr through activated carbon for colour removal. The water source is dam water which currently passes through 100micron screen filters.

I have done some bench scale trials and a 4-6 minute contact time "seems" to work, however i would imagine that a visual inspection cannot determine exactly how well it has worked.

What i am after is some reference to suggested AC contact times for various contaminants...i would imagine that the slight colour in this water is the usual humic/fulvic acids present in surface water.

 

[sbush]

I don’t have any data on recommended carbon contact times; however, I can offer a few tips. Don’t put too much stock in the bench scale results. Bench scale testing should only be a guide to whether an in situ pilot study might be warranted. Your carbon selection might work in a bench scale but fail in a pilot test. Some major U. S. cities like Cincinnati have installed large-scale carbon systems for treating their water supply, but I don’t think color removal is the primary purpose. There are probably more color reduction systems in use in the State of Florida than any where else. In Florida, most of the large-scale municipal treatment systems for color reduction use either: macroporous anion exchange resin, ozone oxidation, or lime-soda softening (reverse osmosis, ultrafiltration and nanofiltration also remove color, but can require more frequent cleaning and maintenance as a result) . Even in large demineralization plants where activated carbon is routinely used as pretreatment, when organic matter such as mentioned above is present, then special organic reduction techniques are typically employed because carbon alone is not as effective on large molecular weight color bodies. If you continue to pursue the use of carbon for your application, I recommend that you look into using a wood or peat-based carbon. This is one of the most macroporous carbons. As a result, it is more effective than coal or coconut shell carbons at removing large color bodies. Norit was once a major supplier of wood or peat-based carbon, and may still be. Norit might also be able to supply the contact time data you are looking for. If you contact them, be sure to inquire about carbon regeneration and/or carbon replacement requirements, as these might need to be performed on a regular basis. Because of it’s highly porous nature, wood or peat-based carbon is also one of the most fragile.

There is no substitute for analytical testing; however, visual inspection of samples in a white styrofoam cup in good lighting is quite effective too.

Be sure to incorporate testing for disinfection by-products too.

S. Bush

http://www.water-eg.com

 

[ivanhoe374]

Yeah it is the disinfection byproducts that i am worried about. Even if i remove all of the colour i would imagine that there would still be some dissolved organics that could form these by products when we disinfect?

I have sent the samples off for lab testing (colour) i was going to get them done for TOC however there is a 2 week waiting time.

Not sure how long a THM test takes?