GaryD

Greenwater Aquaculture

322 posts in this topic

I keep coming back to this concept from an energy point of view. Going back over all the greenwater documents I can find, I am seeing some promising things for a low energy system.

Let's look at an example 8000L system

pump 1200 LPH (5 watt airlift)

turns over tank volume every 7 hours (several times more than the UVI systems)

400L clarifier - 2X 200L drums, remove sludge daily

4 airstones with 5 watt air pump

final stocking rate - 10kg/m3 (possibly up to 15 kg/m3)

number of fish - 160 grown to 500g, 80kg harvest

solar system - 40 watts, with battery enough for 5 cloudy days - $400

So, now you are looking at 160kg of fish a year or running a continuous system with an average stocking of 10kg/m3, which should produce even more (above 200kg/yr). All for 10 watts. This seems really efficient in terms of energy.

Does anyone else have thoughts on the energy side of this?

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It's way more energy efficient than an aquaponics system, but you lose the plant growth in the system, so overall efficiency is lower. The solids that are removed can be added to a different type of growing system though, but this would involve manual labor inputs. Basically you trade electrical energy for mechanical energy typically provided by humans.

Another requirement is a growing area that does not get too cold as heating would defeat the purpose of a low energy system.

It is a cheaper way to get started in growing fish as fish food is optional if growing a fish that eats algae.

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do those numbers look something similar to your system, Ravnis? Do you have 4 air pumps for your 6,000 gallons?

What other fish might be suitable, beyond Tilapia?

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I'm sorry I don't have any hard numbers. When I moved them indoors I had ~300 lbs of fish in the 5000 - 6000 gallons of pool. I was using 2 air pumps that are rated at 5 watts and 9 liters/ minute. I had also given 50 lbs of fish to a friend to start his system with. The air pumps were not sufficient and I should have used 4 at least.

Are you wanting to grow veggies too? If so you are better off with the aquaponic system you had laid out.

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well, I have lots of wicking beds, so I was thinking of pulling water off a system for them. I am more interested in spending the energy to grow fish, cause I can grow plants without any electricity already.

The aeration part is the wild card, here. Even UVI doesn't mention what was required in their test setups. They mention the amount of airstones, but not the airflow or wattage of their blowers. So, it is difficult to estimate what is possible.

Did you have a lot of baby tilapia born in the system? Will you be doing something similar in the future?

Ok, so based on what you said, maybe cut the volume in half for the 10 watts. So, like 4000L with the 2 air pumps. That'd be about 80 fish in 1000 gallons. That's around 80kg per year for 10 watts. Not too bad. If you did a continuous harvest method, you could probably harvest up to 150 kg a year.

I think that's going to be more efficient than the RAS or AP setup. Focusing the energy on aeration, rather than pumping, helps on the energy side of things. This has a lower stocking rate than an AP or RAS (for the same energy level), but it has 3 times the water volume for the same energy, so you end up with more fish.

I wonder if an RBC like Cecil's could be used to help with aeration: http://www.aquaponicshq.com/forums/showthread.php/1428-Small-Scale-Sytem-I-put-together

It seems like you get extra aeration with that for the same water flow, but the algae might be an issue with it.

What I really need to do is setup a greenwater system and a RAS, and run both on 10 watts, and see where the limits of each system is.

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one thing you might consider is start with a greenwater system as spawning in one is kind of "set and forget" no real effort needed, just a place for them to spawn in like clay pots or something. Then if your not satisfied , use the ras or aquaponic system as a growout system. I wound up doing the greenwater system as I had very little money to make a second system and the swimming pool was not being used at the time.

Yes, I will be setting up a greenwater system or hybrid system if I figure out how to keep the solids from the algae from clogging up the growbeds. I think the scrub brush setup holds promise.

I did get tomatoes off the hybrid setup last year , but the performance was mediocre.

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were your settling tanks not working well enough? maybe a swirl clarifier?

The UVI document talks about retention time in the clarifier. It is like 50 minutes, so the water is moving slow enough for solids to settle out. Your pump might be too big!

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The clarifier only settles out some of the algae, the dead cells. The living cells float and will stay in the system. My make shift clarifier was undersized and I was attempting to run a flood and drain system, which did work, but needs more testing and improvement. I started having problems with build up about the 6 th month, worms helped but did not totally solve the problem for me. My rocks were probably too small diameter and needed to be bigger.

I think its worth looking into further due to the possiblity of greatly reducing dependence on commercial feed.

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yes, I think it looks very doable from an energy standpoint. I can see it outperforming RAS systems, even at 1/3 the stocking rate.

We're you experienced algae growth in the flood and drain beds, or mostly solids buildup?

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What is your nutrient source?

I did some experimenting with greenwater systems a few years back and they tend to stop being productive without a nutrient source.

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yes, I think it looks very doable from an energy standpoint. I can see it outperforming RAS systems, even at 1/3 the stocking rate.

We're you experienced algae growth in the flood and drain beds, or mostly solids buildup?

solids buildup. My understanding of solids removal was minimal when I cobbled this setup together. I learned from it and it gets better with every system redesign.

EG. I did use commercial feed in my setup, but was getting feed conversion rates that were way higher than reported in aquaculture material I had read. Example 300 lb of tilapia from 1 50 lb bag of feed. Of course they were eating mosquitos, and other bugs that entered the tank, as well as bloodworm larvae. I have no current method to quantify those inputs.

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What is your nutrient source?

I did some experimenting with greenwater systems a few years back and they tend to stop being productive without a nutrient source.

Most of the greenwater systems still feed commercial feeds, but they see a FCR of 1 or lower. I guess you could add additional nutrients in the form of compost or animal manures, if you didn't want to use feed. Rabbit manure might work, and I imagine duck manure would do well.

But, I think it is easier to feed the fish. There might be a stocking density minimum to keep the algae bloom going.

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This one?

http://procs.gcfi.org/pdf/gcfi_51-25.pdf

31,000 liter tank

1400 liter clarifier - emptied twice a day

13 air stones

37.5 watt air pump

26 fish/ 1000 liters

32% protien feed

24 weeks

End total biomass 13.4kg/m3

Feed conversion 1.41

Daily water exchange 0.23%

Flow rate 1300 liters per hour

Any other species that will work in these systems?

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One of the virgin Island reports clarias species being a possible. I have no idea if they are allowed in your area. They are air breathing fish catfish so would tolerate low 02 levels if they had too.

It occurs to me that one difference I may have experienced but others may not be able to duplicate is the extreme Texas weather. I was getting water temperature of 92-100 F. Which i believe is 33c-37C. Algae growth is considerably higher at this temperature than say 70-80F that would be more typical in virgin islands. It would actually form a thick mat on the surface that I wound up scooping off due to being afraid it might interfere with gas exchange.

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yeah, that's one.

13 air stones

37.5 watt air pump

Was that the wattage of the air pump, or is that the water pump? Did you see any figures for air flow?

And I assume their clarifier is just a bit cone shape tank, right?

So, they reach a 13 kg/m3 biomass with 1.2 watts of aeration per 1,000 L. That's pretty impressive.

I think some carp would do well. You want algae eaters that don't mind pea soup.

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It is very good provided space is not an issue. I doubt the aeration was doing more than working the air lift pump to move the water about. They are good fun to play with, especially with fish that handle the green water. Our little trial here showed the fish in the green water grew faster than those in the clean water. Keep an eye on the ph fluctuations and the early morning oxygen deficiency.

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well, they do have more aeration than the air lift. Aeration in the tank is to keep everything in suspension, stirred up. From the photos I saw, they had air stones around the tank to keep things moving. The airlift is only moving 1200lph for a 31m3 tank, so it's not using that much energy.

It seems like a more efficient use of energy to me. According to my calculations, I could run a 4000L system on 10 watts, maybe even 5 watts. Stocking at 10kg/m3, our standing biomass would be 40 kg, which should be able to produce at least 120kg of fish a year. All from 10 watts (maybe less). I don't think I can reach those levels with the LEAP system.

It all boils down to kg of fish per watt. With RAS, I think I'm looking at maybe 60kg a year with 10 watts.

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The aeration and power consumption is a little confusing. In the diagram they show an airlift pump 1/20hp but there is also a vertical lift pump in the fish tank. I think they are like an asparator.

I think they will have been hitting an oxygen ceiling around 3 in the AM when the algea is chewing through the oxygen.

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yeah, it was confusing for me, too. I don't see air flow rates or power for air pumps, just the vertical lift.

Still, Ravnis had 130 kg going in 19m3 with 10 watts of air.

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I think they will have been hitting an oxygen ceiling around 3 in the AM when the algea is chewing through the oxygen.

very close, I noticed the tilapia floating at the surface with there gills at the surface like they were trying to breath air. This generally happened between 1 am and 2 am. I work the swing shift so generally would watch the system till 4 am. Before the air pumps were added I could stop this behavior by running the pool pump for an hour or two and this would carry them though the night. The pool pump drew 9 amps at 110 volt so ~1000 watts for an hour. Not exactly solar friendly.

This was what prompted me to add the air pumps. I had 4 outlets on them and used one on an experimental air lift I made out of 3/4" pvc pipe and floated it on top of the water by putting it in one of the childs play mats that float. When the air pumps were added they would do the gasping at 4 am. I squeaked by with this because sunrise at that time of the year was only an hour or 2 away. Thus why I say I should have doubled the air pumps, maybe even trippled.

If you go:

pond raising with light stocking as non intensive - lowest stocking density per unit of area

pond raising with lots of blowers as semi intensive - 2nd lowest stocking density per unit of area

recirculating aquaculture as intensive highest stocking density per unit of area

I rank greenwater below RAS system, but above semi intensive.

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the thing is, it really amount to kg per watt.

If I can stock 10kg/m3 with 10 watts of pump+aeration in greenwater, and that will run 4m3, then I have a biomass of 40kg.

If I can stock at 20kg/m3 with 10 watts in RAS, but that will only run 1 m3, then I have a biomass of 20kg.

I thinking running a few air pumps all night at the same stocking density that you had will work. Another issue is temperature, and as you have said, your temps were around 35C (which requires more aeration) at times.

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Your biggest risk with green water is the midnight to sunrise. Generally greenwater will not require aeration during the day because the algea produces oxygen while the sun hits the water.

If you can run timers or daylight sensors to switch pumps on and off you might have a chance. But running solar becomes a storage issue. Shame it was not around the other way.

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well, part of the solar system includes batteries for at least 5 days of cloudy weather. So, I think running stuff over night will be fine (everything has been sized to run 24/7).

But, if we might not require as much aeration during the day, we could turn off some of the air, and just run it at night, saving some power, there.

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Algea is an interesting creature when playing with it in tanks. We recently build a 20 tonne recirc. system and it runs liquid oxygen. Algea caused no end of trouble even though the water was not green. The oxgyen was set around 80% saturation and at night because it was an oxgyen sytem, the oxygen only got down to 70% but then during the day as soon as day broke, the saturation would fly up over 130%. This starts to cause management issues and loads of stress for both the farmer and the fish.

The ideal situation in my opinion for you would be to monitor the oxygen levels and have the air or pumps turn on at a set level and turn off at a set level. That way you could let the algea do the work during the day and backup systems only when needed.

Or

Set up bigger or multiples of the same air pump that can be manually brought online as needed or switched with a mechanical timer . This would take a little trial to find the "sweet spot" in the consumption : production.

Or

The same scenario using multiple air pumps with sunlight sensors for switching. I think this would be easier to manage, especially for those ordinary cloudy days.

I think you are better to at least double the ammount of air pump you think you need and connect them when you build it. Nothing worse then getting to the oxygen ceiling and standing there with an outboard moto...err.... with a bucket lifting and tipping water to save the fish. Or many sleepless nights worrying about them.

Using the green water will use majority of the nutrient up so you will want to take the solids out from the dead cells (orchard or bird netting will do that) and mineralise those for use with the plants. I would avoid cycling the algea through the plant system though.

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