Greenwater Aquaculture

[GaryD]

Hi,

Ravnis mentioned greenwater aquaculture on another thread and thought that it was worth discussing in its own thread.

I have trialed growing fish in a greenwater culture with the algea growing to be the means of nitrification. It has worked well, but growbeds will not function with the thick solid mass that the agae forms.

I have set up a series of tubs that let the algae settle out of the water and pump it back into the tank. While I can't directly hook up grow beds to this system, I have found two good uses so far. One is that my ducks go wild for the algae and the red midge fly larvae(blood worms?) that grow in it. The other is I throw it on my small trial wicking worm bed and the growth is good. I have a watermelon plant that has vines that are ~10ft long and has produced 3 medium sized water melons. The worms either eat the algae or the bacteria growing on the algae. The only main issue I have had has been aphids, ants, and grasshoppers.

The ph of the water runs around 8 and will raise back to that in a matter of hours even when acid is added to bring it down.

You can read an article on greenwater aquaculture by a UVI researcher John Martin......here.

Vivienne Hallman, a Brisbane scientist relied on greenwater nitrification when, several years ago, she raised silver perch in tanks that had no bio-filtration. You can read about her efforts.......here. Her work is important to local micro-farmers because it confirms that greenwater culture is viable (albeit at much lower stocking densities) for some Australian species.

I think that Jim Fah's AutoPot Aquaponics system also uses algae for nitrification.

Greenwater culture is an appropriate technology idea that certainly deserves a closer look.

Gary

[Ravnis]

The advantage of greenwater is its low cost of startup. My cost for my 6000 gallon system was less than $500, including water and fishfood, compared to $3000 dollars for for 1200 gallon aquaponic setup of which I built the grow beds and did all the plumbing. It should be able to grow 1000 lbs of fish easy if I spend a more on a high quality air pump and air stones.

While I feel the aquaponic setup is more productive when it comes to growing plants, the greenwater is ideal for someone starting out or on a budget and wanting to grow a large amount of fish with a low startup cost.

The article by John Martin was where I got the basic idea of how to get started with this project.

[GaryD]

Hi Ravnis,

Those are important figures for people who may be looking to do something about integrated backyard food production (Microponics) but have limited money.

Can you describe your greenwater system in greater detail? Any photos?

Gary

[Ravnis]

I'll try to figure out how to work the camera and upload some pictures tomorrow.
The system is basically a 15 ft diameter swimming pool with air stones. I have put an exit pipe for the water to flow into a tub with a standpipe and drains into a tub below. This then goes into another tub filled with lava rocks . A powerhead with black washer hose connected to it drains back into the pool.

I also have a swimming pool pump and filter. I really dont use the filter and run it mostly on recirculate. The pool needs the extra water circulation at night and on very cloudy days, as the aglae then consumes dissolved oxygen instead of supplying it. Thus the need for a better air supply for higher stocking density. I run the big pump for a couple of hours between midnight and 2 am. I do it manually cause I am up at that time, but could do it on a timer.

I am raising tilapia, but with enough araeation and solids settling buckets, I could run this with other fish, as pointed out by Vivienne Hallman's effort of growing silver perch. The ideal fish would be one that eats algae, and can handle low dissolved oxygen levels. Tilapia is one, but I am sure there are others, I just don't know which ones yet. A fish that could gulp surface air and consumes algae would be great as long as it had a good taste.

The great thing about this is the sustainability. They will grow without feeding, albeit a lot slower. I've read about 25% of the growth rate of fed fish, but if you are looking to not have a feed cost... this will work.

[Ravnis]

It's been too hot for me to do much weeding lately, so excuse the weeds. As can be seen from these pics. THe setup is very simple and inexpensive to both setup and operate.

The big downside is the water used for wicking beds has to be replaced. I use about 10 gallons a week in the one wicking bed.


http://flic.kr/p/8AF7Rz

http://flic.kr/p/8AF6HP

http://flic.kr/p/8AF7yH

http://flic.kr/p/8AF7kp

http://flic.kr/p/8AJaXE

http://flic.kr/p/8AF63k

[GaryD]

Hi,

I love the idea of using algae for nitrification.....and for the other integrations that it offers.

By harvesting the algae, you take the nutrients out of solution (in exactly the same way that vegetables remove nitrates in a conventional aquaponics system) and, in so doing, you pave the way for more integrations including using the algae for fertiliser (as Ravnis has suggested) or as food for other micro-livestock like chickens, quail....and worms.

Algae can even be pressed to remove the oil for use as a fuel.

Gary

[grassroots]

I also wish to try a more self-maintaining system, without too many inputs(pumps & bought food). Thanks Gary for the link to Viviennes' site. It has given me inspiration to push ahead with this idea. I have two spare tanks(1000L & 900L), which I can fill up and see how it goes. When I can get back down to Childers I'll get some more fish. I think five fish in each should do it, what do you think?

[GaryD]

Hi Ravnis,

Thanks for the photos......they what you're doing a whole heap easier to understand. What do you use to harvest the algae?

In reading John Martin's article (in the Aquaponics Journal), I note that they use a clarifier to capture the sludge. I'm not yet clear on whether this includes the harvesting of the algae.

I've read on another site where they use a fabric net to gather up the algae. In other places, they've used a centrifuge for harvesting.

Grassroots.....I'm unclear as to what species would be appropriate.....or how to go about it. Vivienne's experience suggested that silver perch would be OK but, outside of that, it's a matter of experimentation.

Gary

[Ravnis]

For now, I use my two hands and literally scoop it out into a bucket and then give it to the ducks. It clumps together into a semi-solid mass.

When I first came across aquaponics, I was actually looking into making biodeisel. There was a blurb about "bioponics" and I put the biodiesel project aside. I had read about the problem of keeping an algae culture going. This might be a way to get meat and fuel at the same time. I sure haven't had any problem with growing algae this summer, but winter may be a different story.

The tubs, are my clarifier. The reason for the standpipe is to let the heavier clumps settle. I tried using it as a growbed with worms to keep it draining at first, but they could not keep up with the algae growth and it would stop up. I think it's similar to plant matter, they eat the microbial growth on the plant rather than the plant itself. The same seems to go for the algae as well.

Grassroots, A word of caution about this is that oxygen levels drop when when its not bright and sunny, so a way to provide extra air is needed. This could be a pump splashing water or an air pump.

[grassroots]

Hi Ravinis, I would have thought that when the sun is out there would be less oxygen(like in a algae bloom)?
Could you please explain why this is or point me in the direction of where I could find this information, Thanks