# Flow rate.



## Jaseon (4 Mar 2021)

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?


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## dw1305 (4 Mar 2021)

Hi all,


Jaceree said:


> 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.





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


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## John q (4 Mar 2021)

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.


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## jaypeecee (4 Mar 2021)

Jaceree said:


> What do you think is the optimal LPH or GPH for bacteria to its job properly?


Hi @Jaceree 

In external canister filters or internal filters/sponge filters, this is something you don't need to be concerned about.

JPC


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## dw1305 (4 Mar 2021)

Hi all, 


John q said:


> 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


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## Jaseon (4 Mar 2021)

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.


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## dw1305 (5 Mar 2021)

Hi all,


Jaceree said:


> 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.


Jaceree said:


> 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


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## dcurzon (5 Mar 2021)

This is a very good synapsis of IT meetings I have to attend :/


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## dw1305 (5 Mar 2021)

Hi all, 


dcurzon said:


> This is a very good synapsis of IT meetings I have to attend :/


I may have chosen IT for a reason, but it could just as easily have been HR............

cheers Darrel


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## John q (5 Mar 2021)

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.


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