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]

Yeah - lighting is a bugger.  I'm not able to use two of my beds fully right now because the passion fruit is shading everything.  At some point, it will be out of the greenhouse and along the back wall - then I'll restrict its growth inside.  Now, it is a bother though.  That and the pH issue has seriously messed with my desire to grow some lettuce.

Harold Sukhbir said:

Hi Nate/Kobus,

I had installed a 6" x 5' long pipe, pre-raft, with a open slot along the top positioned at approx. 20 Deg angle filled with fine nylon mesh balls (connected on a string for washing your back in the shower) and the learning curve was almost instant. I then switched to the swirl for pre- raft filtering, which arrested approx 80% fines. In an attempt to filter more efficiently i went ahead and stuck some coarse nylon shade material into the swirl which brings it to about 95% fines. Since the mesh size is much larger than what i was using previously it will need cleaning less frequently, time will tell.

Kobus: Light issues, I'm now becoming aware of what,how and where i plant something.This AP seems to want to always continue to teach me something new everyday!

[TCLynx]

Well, if you need some low light plants, I know of a couple that are doing well with quite a lot of shade.  Aloe and watercress come to mind right away.  In an overly wet bed the water cress would be a good choice and the Aloe likes the beds not to flood over the gravel.

[Averan]

So stoked to have found this conversation!  Although it seems to have gone dormant....how are everyone's tests working out now?

Personally, I've been tinkering with a new system design that consists of 3 modules: 2 media beds and 1 raft/tank.  I have a steep hillside and plan to put the hybrid raft bed / fish tank in the middle.  The upper media bed will be flood/drain and oscillate with the lowest media bed which doubles as the sump.  A pump in the sump will push water up into the middle raft/fish bed with a constant flow and split off to feed the upper media bed.  With a 2:1 ratio of media to raft/fish tank I hope that it will completely handle all solids.  The media beds will be stocked full of worms of course.

In my current little micro system, I've got about a 1:1 ratio of fish tank to media bed and have not noticed any buildup that would worry me.  Granted, my fish tank is actually 3 tanks, one overflowing into the next down to the sump.  It is actually a CHOP2 setup with crayfish, mosquito fish and other misc little invertebrates living in the tanks to consume and convert excess wastes.

With my new design (which is much larger, 30'x20') I'm hoping to increase usable grow space by turning the sump into a media bed.

I guess I'm not asking any questions here, just wanting to join in on the fun with others looking to innovate with hybrid designs and biological solutions to maximizing efficiency and output.  :D

[Kobus Jooste]

Hi Averan

 

My system is currently overwintering fish less, but the tinkering with extra sumps is ongoing.  I have a "clean" sump from which water is directed into NFT and a sand bed, while the "dirty" sump is currently just used to add about 200 liters of water volume and perhaps a bit of biological filtration / mineralization.  I decided not to clean it all summer long and did not have any problems with water quality.

Averan said:

So stoked to have found this conversation!  Although it seems to have gone dormant....how are everyone's tests working out now?

Personally, I've been tinkering with a new system design that consists of 3 modules: 2 media beds and 1 raft/tank.  I have a steep hillside and plan to put the hybrid raft bed / fish tank in the middle.  The upper media bed will be flood/drain and oscillate with the lowest media bed which doubles as the sump.  A pump in the sump will push water up into the middle raft/fish bed with a constant flow and split off to feed the upper media bed.  With a 2:1 ratio of media to raft/fish tank I hope that it will completely handle all solids.  The media beds will be stocked full of worms of course.

In my current little micro system, I've got about a 1:1 ratio of fish tank to media bed and have not noticed any buildup that would worry me.  Granted, my fish tank is actually 3 tanks, one overflowing into the next down to the sump.  It is actually a CHOP2 setup with crayfish, mosquito fish and other misc little invertebrates living in the tanks to consume and convert excess wastes.

With my new design (which is much larger, 30'x20') I'm hoping to increase usable grow space by turning the sump into a media bed.

I guess I'm not asking any questions here, just wanting to join in on the fun with others looking to innovate with hybrid designs and biological solutions to maximizing efficiency and output.  :D

[Averan]

What is the purpose of pumping 'clean' water into the sandbed?  Is it also a grow bed full of plants?

I'm thinking of letting the water from my second media bed (twice filtered) drain into NFT tubes before returning back into the sump.  Now I am starting to worry about there not being enough nutrition in the water feeding the second bed (the one at the top of the hill).  I was thinking originally to put worm-feeding tubes in that bed, giving them kitchen scraps to provide a second source of nutrients.  Fortunately, I can work my way up to that if I find that all of the nutrients are getting used in the raft and media sump.

Your current setup sounds a lot like my micro system!  I totally dig the idea of inserting these 'ponds' into unused spaces as extra habitats for all the beneficial natural processes to occur.  I've thought about doing something along these lines but stocking those tanks with crayfish as an extra item to sell to a local Cajun restaurant.  Alternatively, perhaps these could be used as fish hatcheries?  This is what excites me about an approach modeled after nature....nature abhors a vacuum and life loves to fill in the niches!

[Kobus Jooste]

Sending the clean water to the sand is a cautious first step to see how well sand acts as a medium for root crops.  I do not want to run water containing too much solids into it at first.  Remember with a smallish AP system (this is in part also in response to your concern about flowing one bed into another) the nutrients become "balanced" in the water supply and unless you have a super dense first bed, the second should also be getting enough nutrients - this worked in my first system.  Water first went through gravel beds and then to DWC.  No problems.  The "clean" water thus contains all the nutrients in the system released into the water column, and thus the root crops, and the horizontal 4 inch strawberry pipe, can get nutrient water without getting clogged by solids, which only goes to the gravel beds and the dirty sump.

 

I can unfortunately not grow any inverts here because of environmental laws.  We do not have anything edible in freshwater configuration and are not really allowed to import without a mountain of permits and impact assessments.

Averan said:

What is the purpose of pumping 'clean' water into the sandbed?  Is it also a grow bed full of plants?

I'm thinking of letting the water from my second media bed (twice filtered) drain into NFT tubes before returning back into the sump.  Now I am starting to worry about there not being enough nutrition in the water feeding the second bed (the one at the top of the hill).  I was thinking originally to put worm-feeding tubes in that bed, giving them kitchen scraps to provide a second source of nutrients.  Fortunately, I can work my way up to that if I find that all of the nutrients are getting used in the raft and media sump.

Your current setup sounds a lot like my micro system!  I totally dig the idea of inserting these 'ponds' into unused spaces as extra habitats for all the beneficial natural processes to occur.  I've thought about doing something along these lines but stocking those tanks with crayfish as an extra item to sell to a local Cajun restaurant.  Alternatively, perhaps these could be used as fish hatcheries?  This is what excites me about an approach modeled after nature....nature abhors a vacuum and life loves to fill in the niches!

[Harold Sukhbir]

Hi Averan,

You won't have an issue with nutrient as long as you abide with the rules of thumb ratios for fish. As Kobus says, nutrient is transported by the water everywhere in the recirculating system. The latent nutrient in fish waste solids kept in the media are released to the water over time(mineralized) and these will offer themselves up to the system water for the entire AP. So in effect it really is of no consequence what the position is of each component as long as it remains in the loop.

[Averan]

True, if you have enough nutrients to spread evenly through the system.....but on a minimal stocking density I wonder if you might see some nutrient gradients from the inlet decreasing towards the outlet?  This may even be a method of monitoring system maturity; the younger it is the more we'll see gradients in plant size in a media bed.

For your media beds, do you distribute inflow through a grid or simply have it dump in at one end from a single pipe opening?  What are everyone's thoughts on using distribution grids vs single inlets?

[Harold Sukhbir]

 

"I wonder if you might see some nutrient gradients from the inlet decreasing towards the outlet?"

If your AP is given less nutrient(feed) then as you divert from the rules of thumb for fish ratios you won't be able to sustain the plant ration required by the standard. As long as you adhere to the ratios there won't be a case of deficiency.

 

 

"What are everyone's thoughts on using distribution grids vs single inlet"

I'm using both, to me there is no noticeable difference.

[Averan]

I'm using both, to me there is no noticeable difference.

Great!  I'll go with the cheaper and more simple option then.  ;)

[Kobus Jooste]

Averan - in terms of nutrient defficiencies, I'm not sure if you will pick up a gradient.  More likely you will see the most sensitive plant (or the one with the highest nutrient demand) keel over while the tougher ones are still going.

[TCLynx]

Yes, I think that is a very likely situation, where the more sensitive or greedy plants with show signs of deficiency first.  For instance tomato plants will looks their lower leaves to nitrogen deficiency (since nitrogen is mobile in the plants) even while there is nitrogen present in a system.  To an extent it could be that tomato plants sometime just grow too fast for nutrient transport within the plant to keep up. 

And on this same point I have definitely seen certain sensitive plants show signs of Iron Deficiency long before other plants.  Oregano and Nasturtium seem to show Iron Deficiency very early.

 

On this subject I've seen some insisting that running a raft or constant flood system will provide more constant nutrients and therefore help the plants get all they need even when availability is low and that in flood and drain the plants will suffer more from deficiencies.  However my experiences don't necessarily support those claims so the situation is far more complex.  I've seen people Have problems with iron deficiency in a raft but not in their media beds while it's all part of the same system with the same pH.

 

I will venture that you are unlikely to see plants suffering from Lack of nutrients at the end of a line since the nutrients are in solution.  However so people have seen plants suffer at say the end of a long line of NFT or the far end of a raft.  It is more likely that something other than lack of nutrients is actually causing the issue.  For instance in a long line of NFT the water can heat up and become depleted of oxygen which will cause the plants to suffer.  Something similar may happen in a raft bed if insufficient flow or aeration is provided.