Filtration rates, flow, and other questions

No Tom,

It must not be slow, please read what I read. At times I wonder why I write at all if this is the reaction.....

Kind regards,

Dirk

 

Hang in there Prof., you are very much appreciated! I will go back and read again.

 

Hi @Neville
Also going to try building sump system over easter weekend. Gonna use old undergravel filter plates instead of perspex and 32mm pipe from Andrag. Posted in the diy section.
Regards
Washief

 

haha, Prof,

I can see now why you get so frustrated. I re read all your posts and it makes sense to me again. It is all this 'big bore' stuff that got stuck in my head, making me think slower is better, forgetting the first principles of flow rate vs. volume of filter material. My apologies! To try and make up for it, I will quote all the important arguments in my next post, to make it easier for those that come after me, so they just get them again.

Forgiven?

 

Hi. Is 40mm pvc ok for overflow on 4ft tank? And for filter media floss ontop ceramic rings thn lastly bio balls, and is it necessary to add carbon aswell?

 

40 mm PVC is ok for your 1.2 m tank. The carbon that you buy in the LFS store is useless with three days and you should not waste your time with this stuff, it serves no purpose.

Remember bioballs are not such a high surface medium nor is it really good for bacteria because it they are made of plastic. Porous ceramic rings are much better.

Kind regards,

Dirk

 

Hi Tom,

When you put that summary together, I hope you are going to get the facts right. It will be a test for you, if you don't pass........

Kind regards,

Dirk

 

hehe....

No, it is not a summary, and not intended to be. Everyone will still have to read the whole thread. I am just attempting, by quoting parts of some of your posts, to refresh in the readers mind what he read in the beginning and not get side tracked like I did.

The reader must try and think separately about flow rate in terms of tank volume turnover vs. flow rate in the sump. I would put it like this. Prof, rap me on the knucles if im wrong.
The water comes into the sump at a fast rate, the diameter opens up over a large filter medium in the sump and everything 'slows down', only to leave again at a fast rate.

Here goes!

 

Hi Tom,

Ok, this is a nice way of summing up, but sometimes dangerous if one does not know the context in which I have written my comments.

However, your comment about flow rate is not quite correct, the water does not come in at a fast rate, goes over the filter slowly and leaves at a fast rate. The water still comes in at 1.5 times the tank volume per hour in other words also slowly (remember there were comments about flow rates of five times the volume of the tank per hour), but because the filter capacity is high and the flow rate over the filter is lower, it is highly efficient at converting ammonia and nitrite to nitrate. You are almost there....!

Kind regards,

Dirk

 

Darn, I forgot to add to the post, that the reader can click on the arrows, next to the name of the person being quoted, to view that post. That is why I did it in this format.

 

Cool idea! I have a stack of those in storage... woohoo!

@Tom.K, nice summary dude! Yes, I read this whole thread recently but would have to re-read it to summarise it like that. Good job!

 

@Neville
Thanks mate!

 

I eventually got the formula that I was looking for. Well, it ain't a formula, but a calculator, even easier to play with. It demonstrate what I was trying to say and could not put in words. The word I lacked, is velocity. It comes in at a higher velocity, the velocity slows down in the filter and then it gets pumped out at a higher velocity again.

For example:
The water may come in and leave the filter at 600lt per hour. That is the flow rate throughout the filter. Say the diameter of the inlet and outlet of the filter is 40mm and the diameter of the filter is 400mm. Then the incoming and exiting velocity is 13.263 cm per sec, whereas the velocity in the filter is 0.13 cm per second. Substantial slower in the filter!

So that brings me back to my initial question. What is the optimal velocity in the filter, for the bacteria to perform optimally. Surely there is a too slow and a too fast, expressed as cm per sec?

The link to the calculator:
http://www.1728.com/flowrate.htm

(I will be waiting in the corner... :wondering

 

Hi Tom,

Well done, I think that you have got it! Velocity though the filter is what I mean yes. What the optimal velocity is, is determined by one thing and by one thing only, and that is the amount of oxygen that the water is carrying. If the flow rate (let us call it velocity) was low and the oxygen levels in the water also low, then you would not be achieving your goal, i.e. good biological filtration. If on the other hand the velocity was the same and the oxygen levels much higher, then you may achieve your goal of good biological filtration.

Now all things are not so simple. Water has a maximum oxygen carrying capacity but this is critically dependent on temperature. If your temp is high, then the oxygen carrying capacity of the water just simply is lower and then your filter just may not make it, whilst if the temp was lower then it might be ok.

In my slow flow trickle filter, the water that enters filter comes from my pump and just before that all the outlets of the tanks flow into a sump with a 30 cm drop, in other words a mini waterfall during which the water gets aerated strongly and I think this does the trick.

Kind regards,

Dirk

 

Thanks Prof.

 

Hi Prof

How about a pic or drawing of your trickle filter please if you dont mind sharing your design

 

Go to page 7, post 63 for a pic...

 

#63
No, that is the drawing of the sump.
Tiger bard is refering to Prof's trickle filter, which is something else. As I understand it, it is huge an does anaerobic filtering?

 

@Tom.K

Yes, I am refering to the trickle filter.

 

@Tiger barb
I would love to see it as well. Glad you asked.