Previous in Forum: Use of Re-circulation Valve in Condensate Line   Next in Forum: What Books Are Vital for a New M.E.?
Close
Close
Close
6 comments
Associate

Join Date: Jun 2008
Location: Malaysia
Posts: 27

Thickness of Activated Carbon Layers, Fine/Coarse Sand

07/18/2011 4:55 AM

Hi all,

What factor determines the thickness of each layer of activated carbon, fine and coarse sand in a multimedia filter? Any specific formula? I plan to replace all material inside multimedia filter for better function of multimedia filter after premature failure of thin film RO membrane whereby organic foulants passed through the multimedia filters and get stuck inside the membrane unit thus affecting the flow rate.

Thanks

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
5
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30413
Good Answers: 819
#1

Re: Mechanical Engineering

07/18/2011 5:49 AM

In a sand filter, the critical parameter is forward pressure drop, as this determines the backwash point. The area of the filter determines the downflow speed. The backwash frequency is then dependent on the dirt loading, and is a function of allowable pressure drop. Particle size is not as important as bed depth, as the filtration mechanism is that of a labyrinth where the dirt particle sticks to the sand particle, reducing the effective pore size and providing more places at which a similarly-sized dirt particle may impinge.

Carbon filters don't need so much attention as the upstream sand filter, as the activity within this vessel is catalytic and in the aqueous phase. Occasionally, carbon filters will get dirty, so it is more a case of backwashing on time rather than on forward pressure drop.

It would be unusual to combine these two media in a single vessel, as they do different jobs and have different backwash frequency requirements.

Organic foulants on a downstream RO membrane suggests four things:

  • Review the operation of the carbon filter for performance against original design.
  • Review the chemical dosing regime to ensure the correct agents and dose rates, as these are intended to carry organic foulants out of the system in the reject stream.
  • Review the recovery percentage within the RO membrane. If the membrane is being driven to recover in excess of design parameters, then trouble with foulants and membrane life may be expected.
  • Review the chemical cleaning regime for the RO membrane and assess whether this is being carried out at the design frequency or otherwise, for future reference.
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 5)
Guru
United States - Member - USA! Hobbies - Musician - Sound Man Engineering Fields - Mechanical Engineering - More than a Hobby Technical Fields - Technical Writing - New Member

Join Date: Oct 2008
Location: City of Roses.
Posts: 2056
Good Answers: 99
#2
In reply to #1

Re: Mechanical Engineering

07/18/2011 7:26 PM

Dang,

If I didn't know any better I'd say you really know what your talking about .

Good answer!

__________________
Don't believe everything you read on the Internet!
Register to Reply
Power-User

Join Date: Jun 2008
Posts: 356
Good Answers: 13
#3
In reply to #1

Re: Mechanical Engineering

07/19/2011 1:09 AM

Your answer is very comprehensive and excellent. You may probably tell us the issues involved in using molded activated carbon filter in stead of sand & carbon powder layers.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 30413
Good Answers: 819
#4
In reply to #3

Re: Mechanical Engineering

07/19/2011 5:40 AM
  1. They have a different buoyancy, which will screw-up any attempt to backwash them should they be together in the same vessel.
  2. Dirty carbon doesn't work.
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Power-User

Join Date: Jun 2008
Posts: 356
Good Answers: 13
#5
In reply to #4

Re: Mechanical Engineering

07/19/2011 6:24 AM

Thanks!

Register to Reply
Guru
Hobbies - DIY Welding - New Member Hobbies - Target Shooting - New Member Engineering Fields - Civil Engineering - New Member United States - Member - New Member

Join Date: May 2009
Location: Red Hook, New York (Mid-Hudson River Valley)
Posts: 4364
Good Answers: 177
#6

Re: Thickness of Activated Carbon Layers, Fine/Coarse Sand

07/19/2011 11:53 AM

PW, excellent post! You get a GA from me.

I just want to add one thing to help out the OP:

I'm assuming that you're employing the filter to remove unwanted constituents from water. Usually, to determine optimum raw water feed rate a well as minimally accepted filter area and media depth one must conduct "bench" trials and review the the test results to find the most economical and effective removals.

I for one would not utilize sand and AC together in the same filter vessel as it would tend to stir-up and mix together the two media types, thereby negating any backwash operations where you will find that you end up with even dirtier filter and filtrate.

In my experience, the only acceptable use of AC and sand in the same filter vessel would be in the slow sand water filtration process, where you do not employ backwashing to clean the media......the AC layer would be buried several inches down below the uppermost sand layer and utilized to remove or reduce the amount of THM precursors (namely suspended and soluble organics) from the raw water prior to final chlorination. Cleaning of the filter is typically done by scrapping the upper limits of the top layer of sand, which is in essence a biologically active zone called Schmutzdecke.

__________________
"Veni, Vidi, Vici"; hendiatris attributed to Gaius Julius Caesar, 47 B.C.
Register to Reply
Register to Reply 6 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

CaptMoosie (1); krishnan.ng (2); PWSlack (2); RVZ717 (1)

Previous in Forum: Use of Re-circulation Valve in Condensate Line   Next in Forum: What Books Are Vital for a New M.E.?

Advertisement