Media per Fish ratio - when NO GB's and NO Particlates

MartinC

Stuart Chignell wrote:

With toes

Stu that got a snort of laughter from me at my desk resulting in a few puzzled looks from coworkers.

I miss those toes! :wink:

Colum Black-Byron

Gunagulla wrote:

hmmmmm, is that formula for the max feed rate if you remove essentially all solids? Seems like it gives a rather low rate, unless it is per hour, rather than per day!

My old system (with NO solids removal), according to that formula, can only process just under 200g of 45% trout feed per day IF I removed the solids... but clearly it can process more than that without removing solids, so what's going on?

The formula suggests my new system, where I do remove most of the solids, can only process 130g of feed per day, but it appears to be capable of more than twice that so far. It has 3m^3 of a mix of coarse and fine gravel, conseratively SSA=300m^2/m^3, and I've been feeding in the range of 200-400g/day lately...which is probably fairly close to its limit at this stage for the existing bacterial population, as NO2 has been in the ~0.25ppm range a bit, falling if I feed less, and getting to near 0.5 a few times when I feed more. I might have to put some high SSA material in the ST- chopped corrugated 25mm HDPE is what I have in mind, as I increase feeding rates.

With the nitrification rate, I think it also has a bit to do with suspension rates, so how long the water is in contact with the nitrification media. With the GB's, it's got longer time with the gb's, so more time for the bacteria to do it's thing. Where as a moving bio filter, the water moves through the filter quicker (depending on design and so forth.).

Well that's my take anyway. It could be easily wrong. I'm still waiting to see any sort of nitrates in my system. One day. Maybe.

BuiDoi

Gunagulla wrote:

hmmmmm, is that formula for the max feed rate if you remove essentially all solids? Seems like it gives a rather low rate, unless it is per hour, rather than per day!

My old system (with NO solids removal), according to that formula, can only process just under 200g of 45% trout feed per day IF I removed the solids... but clearly it can process more than that without removing solids, so what's going on?.

THANKS GG.. if you, my favorite mathematician can't work it out then it saves me giving up reds for three days.. :notworthy:

..
.Peter
.

Stuart Chignell

I'm no up to double checking Timmons at the mo.

Charlie

The formula is for DWC from memory, I'm not at home at the moment but it was in my RAS notes as well.

Stuart Chignell

I've just gone back to Timmons.

Formula is:

Vmedia=(1.0-Is) x ( RTAN / VTR )

Where:

:funny1:

Vmedia= Volume of media required (m3).
:funny1:

Is = equals the proportion of nitrification occurring outside of biofilter. Ultra consevartive value I=0 but values of 0.5 have been observed in systems. 0.3 is a common design value.
:funny1:

VTR = Volumetric tan processing rate = ATR x Av

Where:

:funny1:

ATR = Area tan processing rate generally assumed to be 300mg/m2.
:funny1:

Av =Surface area of media per cubic meter (m2/m3).

:funny1:

RTAN = Rate of TAN production = MPc/100 x .092 / t

Where:

:funny1:

M = mass of food fed during a time period (mg/t).
:funny1:

Pc = Protein content percentage.
:funny1:

t = time period.

Stuart Chignell

Assume we are designing a biofilter for an IBC stocked at 25kg/m3 and fed at a rate of 3% of biomass feeding with feed of 40% protein content.

750g of food per day and we are using gravel as a media (300m2/m3).

VTR = ATR x A

ATR = 300mg/m2
A = 300m2/m3

VTR = 90,000mg/m3

RTAN= MPc/100x0.092/t

M=750g=750,000mg
Pc=40
t=1 day.

RTAN=750,000 x 40 / 100 x 0.092
=27,600mg/day

Vmedia=(1-Is) x (RTAN / VTR)
Is = 0.3

V= (1-0.3) x (27,600 / 90,000)
= 0.215m3
= 215L of media required for biofiltration.

From this you can see why biofiltration is never a limiting factor in systems that include GBs that process solids but also why biofilters are not essential for systems that only have NFT or DWC plant growing components.

You can also appreciate why IBC systems with only one GB from a cut down IBC can do just fine for a year or so because they have more than enough volume for nitrification even with the solids left in. Once the bed fills up with solids because there is not enough room to process them the system crashes and a new voice is added to the choir saying the GBs don't work.

Stuart Chignell

Clear as mud or at least as clear as settled fish solids? :dontknow:

MartinC

Thanks Stu, but what is "tan"? :dontknow:

Stuart Chignell

Total nitrogen as ammonium and ammonia.

MartinC

Ah yes. Thanks. I remember it now - I couldn't get sin, cos and tan out of my head.

Stuart Chignell

A note on the time period.

I mentioned earlier that while the it is often the case that t=1 day this assumes that the feed is fed evenly over a 24hr period since this is often not the case it can be a good idea to do the calculations using a smaller value for t.

For example t=0.5 days if the fish are fed during the day as in day light. If you are going to do that you also have to use a different value for ATR. ATR should really be given in mg/m2/t so if you have the time period you should also halve the value for ATR.

BuiDoi

...
Tan..... as in sun tan. :oops:

no.. Sin/cos/tan type tan. :headbang:

OK.. so we have a closed Loop RAS.. NO GBs...
You worked out the formula and the required filtering.. :support:

We remove the particulates, and end with clear and clean water, and that media did it's job, and the only left over is Nitrates.. and these slowly build..

How do you remove the remaining nitrates, short of actually doing water changing..
..
.

Stuart Chignell

Yeah I know you can do your own calcs with whatever media you use to work out the number of liters you will need.

I used gravel as an example because it makes the calc more relevant for everyone else.

I haven't done much with di-nitrification components because everything I've worked towards is to intergrate the nitrates into some sort of plant production.

Having said that irrigating the water to a dirt grown crop is a perfectly valid way to use them but it does need a fair bit of water.

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Media per Fish ratio - when NO GB's and NO Particlates

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