How do I remove suspended solid from my system?

[arthoz]

I could let solid particles to settle into sludge inside the clarifier and regularly removed them but how do I capture suspended solid? Does a clarifier is also effective to capture suspended solid? Or should I install other type of filter like fine netting (or bird netting like they use in virgin island university)?

Would allowing water to flow through a duckweed tank could also capture suspended solid or does it only work like a clarifier and collects only sedimenting solids?

I know solids is bad but how bad could suspended solid be? Anyone got a good suggestion for this problem or am I just worrying too much?

[arachdog]

A clarifier will catch some of them. The really fine particles are actually very, very, difficult to remove. A diatomatious earth filter will get most of them but operating one of those is expensive and impractical. The only commonly used method that will catch some of the ultra fines is a protein skimmer, but they can also be difficult to get working in lightly stocked freshwater. A batch settling tank, or a flow through one with a very, very, long retention time ( ie.very big in relation to your flow) would also work.

But you probably are worrying too much, there are a plenty of systems working fine without any ultrafine particle removal strategy. But your right to think that in an ideal world it would be better if they weren't there. They do contribute to you BOD and also irritate the fishes gills. But the reality is, most systems just put up with them.

[GaryD]

Hi Arthoz,

There are three types of solids in an aquaculture/aquaponics system......sedimentary, suspended and dissolved.

The sedimentary solids will settle out once the water velocity drops enough. UVI talks about a 20 minute retention time for the solids to settle out in a clarifier or sedimentation tank.

The suspended solids are trapped by adhesion.......they stick to the bio-film that forms on the media in a mineralisation tank........usually nylon bird netting, manufactured plastic media or similar. Other more expensive removal strategies include bubble bead filters, Nexus Easy Pod, fluidised bed sand filters, etc.

The dissolved solids (which are the only ones that should remain in the system) become ammonia, then nitrite and eventually nitrate........and this happens in a bio-filter.

Gary

[arthoz]

Thanks for all the help. I was planning on going commercial in a few years and I was a bit worried about suspended solid in a large system.

I've visited a friend's canvas fish tank a month ago and it seems that his fishes are doing fine in muddy water with some water lily or something floating on the water to deal with ammonia issue though it's no where near to aquaponics (they had never even heard of aquaponics so I was being polite not to mention it). He had stocked around 6000-9000 catfish in four 10X4 feet (just an estimation of the dimension, had a fuzzy memory on this) canvas tank at 3 feet deep water. The only problem he had was from fish skin disease caused by rainwater from a recent storm and death when the bigger catfish are pecking at the smaller one. But all in all the loss was quite minimal and expected.

The only worry I got is for tilapia. They are very sensitive to water quality and even their taste could be affected by it. I think I've read in someone's blog the concept of "small is beautiful" or something. Does placing large number of fish in several smaller systems to be safer and more manageable in terms of water quality and disease management than hoarding them all in a single large system? Or is it just unnecessary and redundant?

I guess Gary's advise on bird nylon netting would be a cost effective solution. Besides, in long term, expensive and complicated device might be hard and costly to maintain or replace. I would be using rural workers and they might accidentally damage sensitive equipment.

I had a species of pegaga planted in my growbed and their growth is quite surprising. The roots had grown so much that it pushed up the medium basket out of the tank. The point here, I think those roots must have have acted similar to the nylon netting that Gary mentioned because the water is crystal clear except after feeding time when they get a bit murky. I only needed to trim the roots once in a while and suck out the sediment with a pump.

Kangkong roots works the same in my observation. I had slice a chunk of the roots on one occasion after it had clogged the system and the thing looked just like a block of sponge when left out to dry. Someone threw it away before I could test it as a growbed media.

[GaryD]

Hi Arthoz,



I think I've read in someone's blog the concept of "small is beautiful" or something. Does placing large number of fish in several smaller systems to be safer and more manageable in terms of water quality and disease management than hoarding them all in a single large system? Or is it just unnecessary and redundant?


You've probably heard me make the observation about using several smaller tanks to offset risk......although it's probably much easier to manage water quality within given parameters in a larger tank.

Nylon bird netting is effective low cost media for use in a mineralisation tank......particularly if the tank design allows for easy cleaning.

Gary

[arthoz]

You've probably heard me make the observation about using several smaller tanks to offset risk......although it's probably much easier to manage water quality within given parameters in a larger tank.


Could you elaborate on this and give some example? I think I'm a little confused. Does it mean that it is easier to maintain suitable nutrient and dissolved oxygen level and remove solid from the system or does it mean that it'll take less time and effort to manage water quality?

[arachdog]

The only worry I got is for tilapia. They are very sensitive to water quality and even their taste could be affected by it. I think I've read in someone's blog the concept of "small is beautiful" or something. Does placing large number of fish in several smaller systems to be safer and more manageable in terms of water quality and disease management than hoarding them all in a single large system? Or is it just unnecessary and redundant?

I'm not sure where you read that Tilapia were sensistive to water quality. As far as I know they are one of the world's hardiest fish. Not to say that water quality isn't important but you margin for error is far greater with Tilapia than many other fish.

The only risk factor that is mitigated by having many smaller tanks is disease. But to take advantage of that benefit requires strict quarantine procedures. ie. No equipment can be shared between tanks, workers must wash their hands with anti-bacterial soap in between working on every tank, foot baths ect.
If you don't do that then the chances are any disease that does appear will likely spread across the whole operation anyway. Water quality is always easier to maintain in a bigger tank, because conditions will change more slowly.



I guess Gary's advise on bird nylon netting would be a cost effective solution. Besides, in long term, expensive and complicated device might be hard and costly to maintain or replace. I would be using rural workers and they might accidentally damage sensitive equipment.


Yeah I dont know, maybe. To my way of thinking the bio-filter is the last place you want your suspended solids to end up. If you go that route you will certainly need to do partial cleanouts on a very regular basis.

[GaryD]

Hi Arachdog,

The only risk factor that is mitigated by having many smaller tanks is disease.
The far more immediate threat is equipment failure or serious leak or burst. Serious disease outbreaks are relatively rare around aquaponics systems.....probably for the same reasons that disease outbreaks are less common on free range poultry, pig and cattle farms than in the intensive operations.


Could you elaborate on this and give some example? I think I'm a little confused. Does it mean that it is easier to maintain suitable nutrient and dissolved oxygen level and remove solid from the system or does it mean that it'll take less time and effort to manage water quality?
Spreading your fish across several small systems offers some protection against such catastrophic failure.....in that you only lose some fish rather than all of them.

Having several small tanks also offers other advantages......you can keep different species and age groups. This advantage is probably more relevant to micro-farmers.

The downside of small systems is that everything happens much faster.....for better or for worse.

The benefit of larger tanks is that they are, by virtue of their larger water mass, more stable in terms of temperature. It will also take longer for a problem to manifest itself......and for a cure to take effect.

If you connect several small tanks, you achieve consistency of nutrient level (which is why most commercial systems also have more than one tank)......and you also access the temperature stability that usually applies to larger single tank systems.


To my way of thinking the bio-filter is the last place you want your suspended solids to end up. If you go that route you will certainly need to do partial cleanouts on a very regular basis.
My reference to nylon bird netting relates not the bio-filter but rather to the mineralisation tank - which is designed to trap suspended solids.

Gary

[arthoz]

I'm sorry for jumping to conclusion, Arach. It's not what I read about tilapia being sensitive but from what I and many people have experienced here at home. Probably the situation might vary regarding to location. Recently here in Temerloh we have been experiencing shortage of tilapia since a lot of tilapia fingerlings reared in cage in the river died due to something in the water (All of them actually and they've stopped stocking tilapia for a while). I heard it was a parasite or something related to the weather, not really clear on that.

Anyway, I wasn't referring to their mortality rate. Sorry if I made people confused. The thing I was trying to explain is that their "taste" when you cook them is "sensitive to water quality". People here could tell where you've reared the fish and what you've feed them by merely tasting them and this relates directly to the price those fishes would fetch. It is also a grave concern to restaurants and hotels that serve fish.

We've had a lot of problems with people trying a lot of tricks to mask the taste of the fish like putting them in a river cage for a month or so to clear their system or something. I think there's some government or maybe religious regulation concerning fish rearing and feeding which I'm not familiar with. It doesn't only happened to tilapia but also with patin, catfish, etc. A big issue that could either rake in a lot of profit or ruin your business altogether.

[GaryD]

Hi Arthoz,

It's generally recommended that all freshwater fish should be purged before processing.

While not everyone can detect (or even cares about) "off flavours" in fish, it's one of those situations where you have everything to gain, and nothing to lose, by purging.

All it requires is that you put the fish into a tank of fresh water and withhold feed.......for 4 - 7 days (depending on the species).

Gary

[arthoz]

Thanks for the info on purging the fish. We've had a lot of myth regarding to fish purging mostly due to trial and error method. I guess fish purging haven't become much of a scientific method where locals have a lot of their own traditional ways...:p