• You are viewing the forum as a Guest, please login (you can use your Facebook, Twitter, Google or Microsoft account to login) or register using this link: Log in or Sign Up
  • You can now follow UKAPS on Instagram.

Flow rate.

Jaceree

Member
Joined
10 Jan 2021
Messages
105
Location
Wales
What do you think is the optimal LPH or GPH for bacteria to its job properly? Ive heard others talk of over filtration, and under filtration, but i suspect a slower flow through the media is better which gives the bacteria enough time to do its job. If the water is passing through the media quickly how does it have time to do its job? Or am i looking at it wrong?
 

dw1305

Expert
UKAPS Team
Joined
7 Apr 2008
Messages
11,844
Location
nr Bath
Hi all,
but i suspect a slower flow through the media is better which gives the bacteria enough time to do its job. If the water is passing through the media quickly how does it have time to do its job? Or am i looking at it wrong?
No, "dwell time" isn't really relevant. It might have some relevance if you have a wet and dry trickle filter <"or HMF">, where oxygen isn't a finite resource and <"simultaneous nitrification and denitrification can occur safely">.

The "slow flow" scenarios are:
  • If the water is flowing too quickly bacteria are unable to grab hold of the ammonia as it passes by.
  • Rapid flow removes the biofilm from the filter media and it never builds up a thick enough layer, so that
  • simultaneous nitrification and denitrification can occur.
But the whole premise is based upon conjectures that can <"easily be refuted">. This is sewage treatment during the <"Activated Sludge"> process. If a picture is worth a thousand words it is this one. I give you "oxygen" as the only thing that really matter.

ivated_sludge_tank_-_geograph-org-uk_-_1481906-jpg.jpg

Photo by John Rostron, CC BY-SA 2.0, <File:Beckton STP, Activated Sludge Tank - geograph.org.uk - 1481906.jpg>

Raw sewage has a Biochemical Oxygen Demand (BOD) <"of about 400 mg/L"> and water (at 20oC) can hold about 10mg/L dissolved oxygen, but you still treat sewage aerobically if you get enough oxygen into it.

cheers Darrel
 

John q

Member
Joined
6 Jan 2021
Messages
301
Location
Lancashire
Well I was going to say look at the likes of a fluval fx6 which has a flow rate of 3500 l/ph and that doesn’t seem to hamper bacterial growth...

Then I noticed darrels explanation and decided my example was sumwhat lacking.
 

dw1305

Expert
UKAPS Team
Joined
7 Apr 2008
Messages
11,844
Location
nr Bath
Hi all,
Well I was going to say look at the likes of a fluval fx6 which has a flow rate of 3500 l/ph and that doesn’t seem to hamper bacterial growth...Then I noticed darrels explanation and decided my example was sumwhat lacking.
I've been lucky/unlucky to have visited quite a few sewage treatment works and they are quite impressive, although often in ways that make you wonder if a little more spending on modernisation and infrastructure might be a good idea.

It was actually working with waste water that set me thinking a lot more about aquarium filtration. As well as activated sludge treatment, traditional <"Rotating Arm Clinker Beds"> are aerobic wet and dry filters and Constructed Wetlands are just <" vegetable filters"> with plant/microbe biofiltration.

In all these cases the solids are separated out, usually by sedimentation and screens, and then the ammonia rich liquid waste is kept aerated until nitrification is completed.

So my question was "why should aquarium filtration be any different?"

cheers Darrel
 

Jaceree

Member
Thread starter
Joined
10 Jan 2021
Messages
105
Location
Wales
So denitrification happens instantly?

Its hard to wrap my head around that. That any ammonia present is dealt with instantly when it contacts the media. Could ammonia pass through the media in a diluted form then gets diluted each time it circulates through the media? Im making a pigs ear of this eh haha.
 

dw1305

Expert
UKAPS Team
Joined
7 Apr 2008
Messages
11,844
Location
nr Bath
Hi all,
So denitrification happens instantly?
No, it doesn't, but I'm not that <"interested in denitrification"> (the anaerobic conversion of nitrate (NO3-) to N2 gas). I actually actively don't want it to occur <"in the filter">. I'm going to use plants to mop up the NO3- and I'm going to ensure that I always have enough oxygen <"to complete the oxidation of ammonia (NH3) to nitrite ( NO2-) and nitrate (NO3-)">.

I'll give you an analogy, this one is particularly for Paulo (@LondonDragon) and also because I use this forum as a <"form of therapy">.
You are invited, at short notice, to a meeting by your IT services. There is only one agenda item, it is "how do you drink a glass of water?"
Right at the start of the meeting you say "I've drunk water, you pick the glass up and swallow the water", and they say "you aren't here to offer any input, you are purely a box ticking exercise" and "We have already identified the most effective process for drinking water, it is to splash it out of the glass with a spoon and then catch the droplets in your mouth".
The meeting starts, but the only discussion is about the optimal shape for glass and spoon.
Substitute drinking water for "Nitrification". glass for "Canister Filter", spoon for "Biohome, Matrix etc" and plant/microbe biofiltration for "Pick it up and Drink it" and that is where I think we are.
Could ammonia pass through the media in a diluted form then gets diluted each time it circulates through the media?
Yes, that is exactly what is happening in the "Activated Sludge" image, the flocs of microbes are being constantly bathed in ammonia and oxygen. As long as there is enough oxygen nitrification continues.

cheers Darrel
 
Last edited:

John q

Member
Joined
6 Jan 2021
Messages
301
Location
Lancashire
Totally off topic but that example reminds me of a team building exercise where we built a torch and half of the parts were knackered.
 

Similar threads

Top