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]

Over under flow like in a settling filter, and the floating media will add as an extra trap for fines.  I want to be able to pump out the terminal end of the sump into clear NFT, but if I do not slow the water down enough, I will get the fines back into the flow.  I want the pump action to suck the fines into the sump, and then see how long water quality in there remains good.  I'm also going to convert what is currently a raft bed into a fourth flood-and-drain bed and add the plant volume I lost from the raft arrangement into vertical towers, fed from the sump.

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.

[TCLynx]

Hum, very interesting...

 

I'm actually thinking I need to add a bit of a settling tank to catch some of the excess solids as my water goes from an overflow into a few constant flow beds.  Where there is constant flow into media I tend to notice a lot of sliming up and water running over gravel which limits which plants will like growing near the inlets.  I'm wondering if adding a settling tank will help much or if it will simply cause me more work. :)

 

[Kobus Jooste]

Time will tell :).  I started adding small capacity tanks under the beds in order to get my water volume up, and then all these little discoveries came along.  Started me looking at the old trickle filters I still use in aquariums.  They can go for years, but if you do have to clean them, the rough media made it a terrible job.  Thus I want to try soft floating media that I can pull out easily and clean should it ever become an issue.

TCLynx said:

Hum, very interesting...

 

I'm actually thinking I need to add a bit of a settling tank to catch some of the excess solids as my water goes from an overflow into a few constant flow beds.  Where there is constant flow into media I tend to notice a lot of sliming up and water running over gravel which limits which plants will like growing near the inlets.  I'm wondering if adding a settling tank will help much or if it will simply cause me more work.

 

[TCLynx]

well not soft but I've seen people use plastic drink bottle caps as floating media before.  I have it in a couple of bins myself.  Perhaps keeping them in a mesh bag would make something easy to pull out and rinse.

 

I've read in a few very different set ups where people have mentioned having clairifier tanks that they never clean out and I'm starting to wonder if those tanks might actually be providing a benefit to the systems even if they are not being used for "solids removal" I mean all tank walls provide surface areas for bacteria and small amounts of solids being mineralized are a great thing as long as anaerobic situations don't arise.

 

Now in a situation with media, I think one either needs to keep a fairly good flow going through the tank all the time or supplemental aeration might be needed to avoid anaerobic situations.  I've got a few bins with media that are constant flood and only have minimal flow but the water drains from them into a sump tank with supplemental aeration and when pumped is introduced to the fish tank by spray bar so I feel fairly safe that any gasses built up can be outgassed before being introduced to the fish.

[Kobus Jooste]

The "Soft" media is a ball of onion bag netting.  I have made them before and they work very well.  The sump I have is about 150 liters, and I intend pulling water out the one end to NFT and allow water to flow in from the tank to the sump passively.  In such a small water volume, I am hoping that things stay safe. 

TCLynx said:

well not soft but I've seen people use plastic drink bottle caps as floating media before.  I have it in a couple of bins myself.  Perhaps keeping them in a mesh bag would make something easy to pull out and rinse.

 

I've read in a few very different set ups where people have mentioned having clairifier tanks that they never clean out and I'm starting to wonder if those tanks might actually be providing a benefit to the systems even if they are not being used for "solids removal" I mean all tank walls provide surface areas for bacteria and small amounts of solids being mineralized are a great thing as long as anaerobic situations don't arise.

 

Now in a situation with media, I think one either needs to keep a fairly good flow going through the tank all the time or supplemental aeration might be needed to avoid anaerobic situations.  I've got a few bins with media that are constant flood and only have minimal flow but the water drains from them into a sump tank with supplemental aeration and when pumped is introduced to the fish tank by spray bar so I feel fairly safe that any gasses built up can be outgassed before being introduced to the fish.

[Harold Sukhbir]

I too have noticed slime build up TCLynx on the in and out pipes of my constant flow drip bed, but next door the flood and drain doesn't have these symptoms. I also agree that the more complex add-ons(clarifier,net filter,swirl filter,etc) in the system it can create better stability.After my recent add-ons and increased fish load, I've also went ahead and supplemented aeration. I also added a second pump in the new sump to create more flow. Now as i stand there is 200 gallons of water compared with 40-45 in FT. What has always puzzled me is I'm yet to read any ammonia, nitrites or nitrates, but everything has always grown well.

[Kobus Jooste]

Well, I'm still tinkering and two tests out of three have been successful.  First, the fines float into the sump / filter by itsself.  Second, the water movement is enough to balance the water chemistry between the sump and the fish tank.  I upped the pH in the sump and tested the next day, and the system had balanced.  All I need to do now is check if I can pick up DO differences in a trial set-up. 

[Harold Sukhbir]

Any DO differences so far?

[Kobus Jooste]

I have backed off from installing the second pump because I want to re-plumb quite a large section of my beds.  I am having light issues as a result of plants getting big in some of the beds which are making me take a long look at the lay-out.  Will report back as soon as something is known.

[Nate Storey]

I"m using a honeycomb matrix with around 2" diameter channels in my settlement tank and it's perfect.  I've found that with smaller sized media, there's a lot of biofouling and an anaerobic/DO issues.  Every 6 months I'll siphon out the bottom, separate solids and cycle all of my settled solids into my worm bins.  I use the castings from my worm bins to plant all of my seedlings, so everything is closed, and there isn't any waste.  It seems to work quite well for me.  Kobus, I would watch your onion bag media.  I think it will work  in the short term and foul in the long term.  You might try something with a less dense structure?  I wish I could get you some of this honecomb media.  I don't even know where it came from though. . . One of those "I got it from a guy who got it from a guy..." kind of deals.

[Kobus Jooste]

Nate - thanks for the info.  The idea with the open sump and the onion bags is in part to be able to get to it rapidly and clean it if needed, but also that it is supposed to only trap the fines that are floating in my system, and not act as a "first stage" filter medium for all my stuff.  That said - I am still cautious of the risk and will keep an eye on things.  The sump can easily be isolated from the fish tank, serviced and activated again if need be.  I anticipate a 6 - month service cycle too.

 

We used the onion bags in small pond filters years ago, so I have seen them gunk up pretty badly before.  What I do not know, is how long it will take to do the same on a dose of fines.  In a way, I'm hoping to be able to leave the sump untouched as long as possible, as I see a trade off in terms of DO lost because of BOD and mineralization VS nutrients gained from the sump mineralization process.

Nate Storey said:

I"m using a honeycomb matrix with around 2" diameter channels in my settlement tank and it's perfect.  I've found that with smaller sized media, there's a lot of biofouling and an anaerobic/DO issues.  Every 6 months I'll siphon out the bottom, separate solids and cycle all of my settled solids into my worm bins.  I use the castings from my worm bins to plant all of my seedlings, so everything is closed, and there isn't any waste.  It seems to work quite well for me.  Kobus, I would watch your onion bag media.  I think it will work  in the short term and foul in the long term.  You might try something with a less dense structure?  I wish I could get you some of this honecomb media.  I don't even know where it came from though. . . One of those "I got it from a guy who got it from a guy..." kind of deals.

[Harold Sukhbir]

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!