Hybrid biological filtration for mixed systems?

[Kobus Jooste]

As any good accidental discovery had developed in the past, my thoughts on this topic grew out of "unfinished business" and accidental observation.  I always wanted to add a sump to the system, as I had too little fish tank volume to run all the beds in flood and drain mode.  I have raised beds thus had unused space underneath (the groups pic is of my system being described here).  I shoved a sump made from a 200 liter plastic bin underneath a bed, and coupled it to the IBC roughly at the 700 liter line with two 75 mm fittings.  Water can flow in and out freely as the system floods and drains.  The intention was to allow some of the beds to drain directly into the sump, but I got busy with other stuff.  Suddenly the IBC cleared up beautifully, and it dawned on me that I inadvertantly added a clarifier and not a sump.  Fines were floating up and into the sump, and settles in stead of flowing out again.  Now I have two options - siphon the fines out once a month and figure out if it goes back or gets tossed, or add media to the sump and turn it into a biological filter.  There are pros and cons to both options - one is more work and as we see from many raft operators, they are turning their net tanks into media beds to get better performance.  I cannot plant this sump up, thus it will become a sink for nutrients, where biological processes will flux some of it back to the water column.  This process works for wetlands, and I'm wondering what it will do to my little set-up. 

[Kobus Jooste]

The more I think about it, the more I think that for linited space applications, some form of biological filtration slotted in underneath beds could be a useful way of being able to squeeze a little more fish and plants into a small space.  If we break aquaponics back down to the basics, we convert fish waste into nutrients for plants using media beds or various filter stages.  Now we all like the idea of media filled beds because we like to have less work, and we do not have to clean these regularly.  Now what if we were able to have some nitrification sites in the system that are perhaps not well lit enough to support plants, but by the nature of their design, these sites nitrify without going anaerobic?  What we would have is more nutrients available to plants, and more bacterial surface area to deal with fish waste.  Now let us splice in another thought.  In aquaculture waste language we have settleable solids, suspended solids and dissolved nutrients.  The plants can deal with the third, the media beds grab hold of the first, but the middle customer is tricky.  They like to settle out in clarifiers or other slow-moving environments that we typically do not supply in aquaponic systems without filtration. 

 

So what am I tinkering with?  How about feeding water from the fish tank into settling tanks.  Set the inflow and outflow high enough that it gets "clear" water flowing in and out, which allows only the fines to settle out in time.  Now you have two options.  Toss in some detritus feeders or, if you are in a country where those are not available, toss in floating type biological filter media.  I think there are three possible outcomes - I do not want to think about the negative ones yet:

• You increase your water volume by using "greenhouse voids"
• You settle out the fines that sneak through your media in any case, fouling the fish tank water
• Because we are working with relatively small water volume, constantly replaced by water movement, I do not think we have a risk of the filter body going anaerobic under moderate loading, thus the sites should have the potential to flux nutrients back into the water column.

I would obviously have to keep my eye on DO levels and make sure that the filters do not become clogged up, but I'm sure that this could be a viable method of upping your water volume in a confined space.  In my case, I am stretching a 1000 liter tank, run at around 800 in the past, to a system with around 1200 liters of water in it (fish only have access to 900 of those).  I increase my media surface area, and I find a way to deal with fine particles in the water, thus loading the new filters very slowly.

[Harold Sukhbir]

Hi Kobus,

Recently added a raft to my Ap system and converted a 6" pipe abt 4ft long mounted it horizontally with a 10 deg angle,slotted a channel, inserted with netting, to act as a net filter.It worked fine for abt 2 days until it almost overflowed. I now have an appreciation of how much solids our beds do have to process! Taking this much solids out of the system is simply unacceptable.I'm now designing a swirl filter to be be the main solids remover, which brings me to TC's suggestion of a remote digestion unit(with added aeration) fitted into the AP loop.There is an advantage here of processing close to maximum solids allowing more nutrient to become available for the system.The fines I'll have to live with as I'm low density on fish it will probably not be too large a problem, you said it yourself, your sump/clarifier cleared up an entire IBC.(Thank you for the idea) I think that a swirl filter is better than a net filter for me because the solids can remain in aerated water for longer processing time and its not as cumbersome and messy as the net filter. I think a properly sized and designed swirl is as good as any clarifier.

[Kobus Jooste]

That swirl will work I'm sure.  I have got a lot of gravel going for the IBC, but was still surprised to see how much fines settled out when I set up the first balancing tank.  It will take a very long time to foul, so I will watch it for now to see what I am going to do. 

Harold Sukhbir said:

Hi Kobus,

Recently added a raft to my Ap system and converted a 6" pipe abt 4ft long mounted it horizontally with a 10 deg angle,slotted a channel, inserted with netting, to act as a net filter.It worked fine for abt 2 days until it almost overflowed. I now have an appreciation of how much solids our beds do have to process! Taking this much solids out of the system is simply unacceptable.I'm now designing a swirl filter to be be the main solids remover, which brings me to TC's suggestion of a remote digestion unit(with added aeration) fitted into the AP loop.There is an advantage here of processing close to maximum solids allowing more nutrient to become available for the system.The fines I'll have to live with as I'm low density on fish it will probably not be too large a problem, you said it yourself, your sump/clarifier cleared up an entire IBC.(Thank you for the idea) I think that a swirl filter is better than a net filter for me because the solids can remain in aerated water for longer processing time and its not as cumbersome and messy as the net filter. I think a properly sized and designed swirl is as good as any clarifier.

[Harold Sukhbir]

Found a design for swirl filter and explanation on manufacture if anyone's interested.

 

http://www.michigankoi.com/Filter-Systems/Vortex-Settling-Chambers-...

 

[Harold Sukhbir]

Hi Kobus,

You said:

Now what if we were able to have some nitrification sites in the system that are perhaps not well lit enough to support plants, but by the nature of their design, these sites nitrify without going anaerobic?

 

I think that It's a great idea.If they are small and placed in satellite positions within the system after a solids filtration point they will enhance the biological processing capability and improve overall water quality and speed up system maturity, so happy fast growing fish and plants!

Of course as you said we'll have to overcome our idea of relying on this standard of media beds as our only means of biological processing.The long term benefits will far outweigh the initial cost as well. Ap appeals to new people by it's simplicity but as a dedicated practitioner i have to always be on the lookout for ways and means of improving my system. Here's a link for filter designs.

 

http://www.biofilters.com/LONGPATH3.htm

 

 

[Kobus Jooste]

Thanks for the bio-filter summary - it is nice and simple compared to some of the aquaculture stuff I have.  I think you made two goood points.  First off, I do not think the average AP enthusiast is looking towards creating as much trouble for themselves as a complex hybrid unit can become.  That said, I think that for me, the opportunity is exactly what I have been looking for.  My system's intended goal is to try and squeeze as much as possible out of a small space.  With raised beds, I have a stack of opportunity to add nitrification sites.  In the end, this may allow me to put the rules of thumb into perspective by having far more nitrification surface area, not by overloading the planted media beds. It will also serve a second purpose - I am trying to "clean up" my water fed to the NFT sections of the greenhouse, as a single pass through the gravel still allows fines through and after a few months, I have gunky roots.  So I am thinking media bed for coarse filtering, a few hundred liters of settling tank / media filled structures underneath the beds to suck the fines out of the picture, and then a second pump giving the NFT good clean nutrient rich water.

 

The second issue is to reach the conclusion that not all the nitrification and mineralization sites in a media based AP system need to be plant beds.  While we moved to media beds to simplify the system, returning some of the components to the media bed system could perhaps allow for 10% more fish or 20% more plants in the same area.

Harold Sukhbir said:

Hi Kobus,

You said:

Now what if we were able to have some nitrification sites in the system that are perhaps not well lit enough to support plants, but by the nature of their design, these sites nitrify without going anaerobic?

 

I think that It's a great idea.If they are small and placed in satellite positions within the system after a solids filtration point they will enhance the biological processing capability and improve overall water quality and speed up system maturity, so happy fast growing fish and plants!

Of course as you said we'll have to overcome our idea of relying on this standard of media beds as our only means of biological processing.The long term benefits will far outweigh the initial cost as well. Ap appeals to new people by it's simplicity but as a dedicated practitioner i have to always be on the lookout for ways and means of improving my system. Here's a link for filter designs.

 

 

[Harold Sukhbir]

Kobus said:

"perhaps allow for 10% more fish or 20% more plants in the same area".

 

If we total the bio mass of fines in a system it could probably rival the weight of solids in our AP systems. If these "sites" are regulated to process only fines that 10-20% ratio could be way more. Part of the maturity in a system is it's ability to convert ammonia as quickly as possible, while this process takes time to "evolve" our media beds, additional dedicated nitrification sites will surely accelerate this process, where the rule of thumb for maturity is approx. 1 year this can be reduced to probably 6 months?

[Kobus Jooste]

I'm not sure about whether we will be able to push the maturing speed of a hybrid system up, but it could be interesting - the nitirification process will have to mature in the fines units too though.  Also, I do not want to load my small system with too many fish because I want to be able to continue using cascade aeration.  having tons of nitrification sites will chew oxygen!  I want to stick to 40 - 50 fish in the IBR tank, and see how much plants I can ultimately sustain.  I'm going to have two "balancing tank / nitrification sites" to begin with.  Together, these will be around 200 - 250 liters of water in constant communication with the main tank (should stay aerobic) but linked in such a way that the solids stay behind in the tanks where they will get trapped on biofilter media.  What one can also do is pump out of these fines filters with small bilge pumps if you can create a "clean" compartment for the pump, thus forcing further water exchange if passive flow is not enough

Harold Sukhbir said:

Kobus said:

"perhaps allow for 10% more fish or 20% more plants in the same area".

 

If we total the bio mass of fines in a system it could probably rival the weight of solids in our AP systems. If these "sites" are regulated to process only fines that 10-20% ratio could be way more. Part of the maturity in a system is it's ability to convert ammonia as quickly as possible, while this process takes time to "evolve" our media beds, additional dedicated nitrification sites will surely accelerate this process, where the rule of thumb for maturity is approx. 1 year this can be reduced to probably 6 months?

[Harold Sukhbir]

I see. At least with additional small pumps, if water is moved around as with the initial pump, you'll get more flow rate and aeration of what's already existing.

[Kobus Jooste]

Having given it a bit of thought, I thought I will take the balancing sump / clarifier concept a bit further.  I really wanted to pump clean water out of this section of the system, in order to have NFT that is not all clogged up.  This water stream could also eventually be used in a seed germitation tray should I get that far.  I will try to compartmentalize the sump with some polystyrene sections and floating media in two of three sections, and a open last section housing the pump.  That should allow me to get to a clear water scenario as well as a good mineralization site.  The floating media is cheap (I make it myself out of rolled-up onion bag netting.  I buy it in bulk, cut 1 meter sections and roll it into a ball.  This gives a large unit with good surface area that can also be removed easily and cleaned if they get clogged.)

[Harold Sukhbir]

Are you creating "Pockets" arranged in series and terminating at the pump? Will this slow the water currents so solids "fallout" may occur? And I'm still trying to grasp the part about role of the floating media.By the way, adding the swirl has improved the water quality and i suspect enhances the over performance of plants. I think you are right about the effects of additional nitrification sites besides our beds. Since I've added the swirl my horizontal net tank can go for 5-6 days without cleaning, and solids can remain for longer periods, so more mineralization time.

[Harold Sukhbir]

Call me crazy, and i guess you're rubbing off on me KOBUS!, but i added some 1/2 lb fish to my system about 5 days ago.I want to push the envelope(or in this case the entire post box) and see what happens. There is now 24 Tilapia, I'd say.... averaging about 1/2 lbs, total weight about 12 lbs, in my CHIFT of 40 gallons. I know this is way too much for my system but with the added swirl and horizontal net tube, guess I'm either getting brave or foolish(won't know which one just yet). The fish seem their usual happy selves so far. I'll monitor as they grow and will cull some if i notice any water or fish problems. So we're looking at approx 1.5 gal per lb for 1 lb/fish grow-out.Any input?


Harold Sukhbir said:

Are you creating "Pockets" arranged in series and terminating at the pump? Will this slow the water currents so solids "fallout" may occur? And I'm still trying to grasp the part about role of the floating media.By the way, adding the swirl has improved the water quality and i suspect enhances the over performance of plants. I think you are right about the effects of additional nitrification sites besides our beds. Since I've added the swirl my horizontal net tank can go for 5-6 days without cleaning, and solids can remain for longer periods, so more mineralization time.