arachdog

Novel and cost effective bio-filter media.

73 posts in this topic

I thought I'd open the floor for suggestions for bio-filter media. I'm constucting a large bio-filter (800L) so I need to find something cheap. But I also want it to be easy to maintain so I will only consider suggestions that will be free flowing and clog resistant. I know Gary uses oyster shells which I haven't ruled out, but I think they will be too heavy for a filter this size. Also I'm not that plussed about their surface area. I was thinking perhaps shredded plastic from a recycler but I've not seen it in person so I really dont know how free flowing it will be. Bio-balls would be nice but at the cheapest I can find them it would cost over $1200 to fill.

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Spiderpup:

Buy a cheap paper shredder (Office works = $ 50) and shred used plasic milk bottles. Not only are they food safe, but they are light weight, easy to replace, cheap and there are lots of them around. Take off lids and labels, open out flat and shred to your hearts content.

Cheers IanK. :D

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Interesting idea BB. Although there a lot of them 'around' actually getting my hands on 800L worth might be quite a bit harder. Also what do you think the chances are of a cheap paper shredder surviving to shred the full 800L are ? Other than those points It doesn't sound like a bad idea.

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Hmm now I'm thinking maybe mussel shells. Still quite heavy but I think they would have a fair bit more surface area than oyster shells. I'm still a little bit worried that the shells won't be able to handle their own weight and will crush down too much and clog. The best density is 500g/l apparently so that means the bottom layer of mussel shells will have to support 400kg over about 0.2m^2.

Reference:

http://www.freepatentsonline.com/EP1383591.html

Somebody has patented a mussel shell bio-filter for removal of VOC from a gas stream. Made me laugh how they talked about how environmentally responsible they were because their 'invention' uses up a waste product. But in reality their patent over such a ridiculously simple idea is actually going to limit widespread use in this application for at least 20 years. It doesn't cover use in aquaculture thankfully.

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Hi Ian,

Yes, I thought it was a novel idea, too......a bit like PVC ribbon but actually food-grade plastic.

Arachdog.....

I've tried polystyrene beads - very light and relatively cheap - inclined to clog a bit. It might be an option for your 800 litre bio-filter (would cost less than $200 to fill) - but I'd suggest you a mechanical filter to remove solid wastes first - use a rotary swing arm to ensure even distribution of water

I've also used manufactured plastic media (Kaldnes K1) - great surface area - clog-resistant - not as light as polystyrene beads but much lighter than oyster shells and far more expensive.

Gary

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Hey 'dog,

How big is your system going to be if you're planning to use an 800 litre trickle filter?

Gary

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Not that big, 1500L to start with. I realize 800L is probably well over-sized especially if I used bio-balls, but I'm planning on pushing the limits in terms of stocking density so I don't want a lack of bio-filtration holding me back. Down the track, when I've found the oxygen limit, I might experiment with removing media while closely monitoring the ammonia and nitrites to find out exactly how over sized it is.

Mechanical filtration will be my untried and untested home made 10um rotating screen filter which if it functions as designed, should keep the bio-filter pretty clean. To ensure even coverage in the bio-filter I was actually leaning more towards a distribution plate than a spray bar. You might be able to sway me though. What do you see as the main benefits of the spray bar?

I'm not keen on the expanded polystyrene beads. Apart from clogging I believe they are quite prone to channeling. The last thing I want is unreliability.

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thought you might like to See my bio filter for my pond i use around 1000 40MM dia bio balls in a large stone pot the pot has a pond pump attached to pump pond water out and over the sides as a water feature i have shaped the inside of the pot into a cone shape at the base where the pump outlet lies as a result the bio balls are kept suspended in the rising column of overflowing water i like these bio balls as they have about the same buoyancy as the water and don't need much to keep them moving regards bart

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Cheers Bart. Looks good. Keeping the bio-balls moving is a good idea as it should keep them free of excessive bio-film. So how many litres did 1000 X 40mm bio-balls end up filling?

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Hi 'dog,

Have you ever made any attempt to quantify the amount of bio-filtration your getting out of your oysters shells Gary ?

Not exactly....but what I can say is that I have supported 44 jade perch (at an average weight of 550gms).....in 700 litres of water......using two 65 litre trickling bio-filters filled with oyster shells.

I used filter foam to trap solids and I was draining spent particulates from the base of the bio-filters once per week.

Under this regime, I actually found the development of bio-film to be more of an issue than ammonia levels. I resolved this by blowing air through the pipework in the system at the same time that I serviced the bio-filters each week.

I am currently supporting 20 plate-size Barramundi using the same set up.....and a 235 litre flood and drain bio-filter filled with clay pebbles. Given the water quality needs of Barramundi, this is not ideal but it's the best I've got until I get one of my new fish tanks operating.

The only way to accurately determine how much bio-filtration that you need, given all of the variables (volume of water, fish biomass, fish species, feed protein levels, ambient temperature, feeding rate, etc) is to test the water and add bio-filtration until you achieve a balance.

To ensure even coverage in the bio-filter I was actually leaning more towards a distribution plate than a spray bar. You might be able to sway me though. What do you see as the main benefits of the spray bar?

I actually use water distributors (plastic bowls that sit in the top of the plastic drum bio-filters - with holes drilled in their bases) but deflector plates would probably be better over a larger area. Both of these have the advantage (over spray bars) in that there are no moving parts to gunk up.

Gary

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Not exactly....but what I can say is that I have supported 44 jade perch (at an average weight of 550gms).....in 700 litres of water......using two 65 litre trickling bio-filters filled with oyster shells.

OK cheers Gary. I know there's a lot of factors to consider but its nice to get some more ball-park information. It helps me to confirm my suspicions that my bio-filter is way over-sized even with oyster shells its probably 4 times bigger than needed, which is what I was hoping.

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Have you considered using 200 litre plastic drums as bio-filters rather than your 800 litre container (which may be handy for other AP purposes)? The drums will hold oyster shells easily enough.....they're cheap and you can start off with a couple and add more if your testing confirms the need.

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Have you considered using 200 litre plastic drums as bio-filters rather than your 800 litre container (which may be handy for other AP purposes)? The drums will hold oyster shells easily enough.....they're cheap and you can start off with a couple and add more if your testing confirms the need.

The tank is actually 1000L but I plan on using 200L as a sump. However it's quite tall and narrow 700mm at the top narrowing to 620mm at the bottom. For me thats too narrow to grow fish to plate size. I'm not saying it can't be done, I just don't think its fair on the fish. It could be used as a fingerling tank but its really to tall so a lot of the volume at the bottom would be wasted. So all that it is really suitable for is a bio-filter.

I am think about getting some barrels going though for early grading purposes and down the track quarantine tanks.

Oh and the btw this is going to be a pure aquaculture venture. Although I love the idea of aquaponics. This particular system is going to be somewhat of a small scale pre-commercial trial, and I believe aquaculture has the potential to offer greater returns per man hour invested, and per square meter of land used. Both of which I am very short on.

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Oh for cripes sake Arachdog. Just build three connected RBC's like this one and be done with it. ;)

removal effeciencies:

RBC 74-83%

Trickling 23-51

greenhouse.jpg

From: Small Scale Aquaculture - Steven VanGorder

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Perhaps, one day Cecil :) I do like RBC, but its worth noting that its difficult to get those efficiencies to translate into system wide efficiencies. To do that you need to use the freedom the RBC has given you to reduce your pumping costs. The ultimate way is to do that is to use purpose built low head pumps, but that means every other component in you system also needs to be low head. There's probably also some savings to be had just by using a smaller standard pump to service those other components (particle filters, growbeds), but not as much.

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OK here's another bio-filter media for you all to consider. Tire Derived Rubber Particles (TDRP). If you believe this study:

http://www.google.com.au/url?sa=t&source=web&ct=res&cd=3&ved=0CBYQFjAC&url=http%3A%2F%2Fwww.environmental-expert.com%2FFiles%255C5306%255Carticles%255C11538%255C257.pdf&rct=j&q=rubber+crumb+biofilter&ei=_AewS5j2D9CIkAXUvrmRDQ&usg=AFQjCNFYeVE20wkuVENWQm8EIF3eTFVlgw

Then it has good nitrification ability and doesn't leach anything toxic. Although I'm not entirely sure of the validity of their toxicity test with regards to aquaculture\aquaponics.

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Hi Arachdog,

Sounds interesting. I'm like you, however, in that I would like to see more evidence of the non-toxicity claims before I committed to use of the media.

I've come across some very ordinary compounds in tyres.....like tyre sealants......and that's before we begin to analyse what's in the tyre material itself.

My mind's open.....but I'd want to see some independent analysis.

Gary

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Yeah some more data would definitely be good. As far as I know this was an independent test but it wasn't very thorough. They only soaked the rubber for a very short time, and then only tested it with two organisms. Then obviously they did no testing whatsoever on weather or not the organisms were accumulating toxins that may not harm themselves, but make them toxic to eat.

I don't think anyone would argue that tires don't contain some undesirables, its more a question of whether or not they actually leach out in significant quantities either contaminating or harming the fish, or stay locked up within the rubber, doing no harm whatsoever. Only one way to find out for sure really...

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OK........but let us know if you start to feel sick......or grow some extra bits.

Gary

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OK, TDRP is out. Not because I was too concerned about sprouting extra bits. But a more pragmatic concern, even though they make you pay to take the tires away, once they've run it through a shredder and pulled the bits of metal out, they still charge $1/kg in anything less than a ton. It would still cost me $500 to fill my filter with, lets be honest, a far from perfect media. As a side note it sounds like there is probably good money to be had ripping up the matting at childrens playgrounds. They are practically paved with gold.

Which brings me to my next suggestion. Recycled shredded HDPE. Should work well as either a trickle filter or a moving bed filter. $850/T which although I don't know exactly how well it packs, should be at least 2000L of media. 42c/L ain't bad, sure beats kaldnes at $4/L. Surface area is going be very hard to work out since its all irregular shapes but I'll give it a go when I've seen it in person.

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OK all sorted. I went to go buy some shredded HDPE but came back with something far better. I believe I've read about someone else using them but can't remember where.

Soda bottle lids! They are made of some sought of PE not sure if its HD or not but they seem to have pretty much neutral buoyancy. They look absolutely perfect to me, practically little kaldnes wheels.

~30,000 lids

~600L

~100kg

~260m^2/m^3 (very conservative estimate, lots of stuff going on inside the cap that I didn't count)

One carton of beer.

Half the SA of kaldnes but 24 times cheaper, works for me.

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Hi Arachdog,

I like the sound of both shredded HDPE and plastic bottle caps.

Light (compared to my current favourite - oyster shell media), very cheap and inert.

The only concerns I have would be the particle size for shredded HDPE (very small media will clog in a bio-filter) and the potential of the bottle caps to retain solids and water creating anaerobic zones which deplete oxygen (rather than add it as trickling bio-filters are meant to do).

Of course, you could resolve that issue by drilling holes in the flat section of the caps......all 600 litres of them.;)

Gary

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Haha, no I won't be drilling holes in all the lids. 5 seconds a lid = 40+ hours of mind numbing tedium, I don't think so. But I agree they don't make great trickle filter media with their propensity to pool water. So I'm going with the moving bed instead, where I think they will work brilliantly. The allure of a maintenance free bio-filter was starting to sway me anyway but the media I have dictates the choice now.

The shredded HDPE I saw didn't thrill me at all. It was made from poorly rinsed chemical drums, including possibly DDT and other 'historical' chemicals, and it still had all the labels on.

So as you can imagine I was very relieved when I found the virgin, food grade, sodacaps.

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