I'm resurrecting this thread because it seems every 6 months or so I go down the aquaponics rabbit hole to research feasibility. I'm focused on looking at things through a low energy intensity future lens.
First off, if you want an overview of aquaponics and the latest academic research you can check out here:
https://link.springer.com/content/pdf/1 ... 5943-6.pdf
I will note that I am much more interested in fish production than produce production. This is because it is quite easy to produce vegetables in a variety of ways at household scale, but extremely difficult to produce animal protein at household scale without lots of external inputs.
The way I see it, you basically have 2 options if you are interested in household-scale aquaponics (not interested in selling commercially):
1.
Recirculating Aquaculture System (RAS) - this is your basic backyard aquaponics setup. Components include a fish tank, grow beds, solids filtration, biofiltration (often done by grow bed material), some kind of pump, and possibly aerator.
Advantages
-more control over variables like water quality
-wealth of resources available online for DIY construction
-high fish stocking density possible (1lb of fish per 5 gallons of water)
Disadvantages
-requires constant electricity
-large biofilter and solids filter require a lot of extra material
-more complex system means more possible points of failure
2.
Still pond system - this is an environment that utilizes natural filtration and aeration. This requires time for micro-organisms to establish themselves in the system.
Advantages
-no external filters needed (although there will need to be surface area for bacteria to colonize)
-no electricity needed
-less complex system means less maintenance and labor needed
-fish will likely eat more insect larvae due to still water, reducing feed requirements
Disadvantages
-low fish stocking density (1lb per 24 gallons)
-less control over water quality so less room for error
-natural aeration necessitates a much higher water surface area to depth, which takes up more ground space
So now that we have that overview, let's build out a basic system. I'll lay out a few assumptions that are particular to me, but of course it will depend on one's own situation:
-The system will only be operational from late spring to early fall so that I don't have to spend energy on heating it in the winter
-I will use common baitfish for human consumption*
-My plants will be duckweed to provide fish feed (they would probably grow in seperate shallow beds so they aren't blocking gas exchange in the main tank)
-The system is located outside (probably with a net over it to keep larger critters out while allowing insects in)
RAS
So let's say we want size a system for
120 lbs of fish output a year (assume 2 breeding cycles, harvesting 60 lbs each time). Here's what RAS system would need to look like:
-300 gallon stock tank
-55 gallon drum for biofilter
-55-100 gallon drum for sediment filter
-duckweed bed
-pump*
This would be a very effective system. I'd have to build in redundant power and backup systems to prevent fish death when things fail. 55 gallon drums can be found used pretty cheaply, so costs on this likely wouldn't be prohibitive.
Still Pond
Now let's size a system that should take up similar amounts of space (625 gallon stock tank with 8 ft diameter x 2 ft height). Assume I have to displace 25 gallons of space for gravel at the bottom to facilitate a natural biofilter, I'll go with 600 gallons as the capacity. Such a system running 2 cycles a year would give me a total of
50 lbs of fish output annually. Certainly not as much output as the first system, but considering there is no electricity input, less materials, and likely less labor required to maintain the system, I'd still call that pretty good.
I couldn't really find data on minnow nutrition, but since they are comparable in size to anchovies, I'm going to assume a ballpark figure of 93 grams of protein per raw pound. This means in the intensive system we're talking about 11,160 grams of protein annually and in the extensive system we're talking about 4650 pounds of protein. If we assume that the average person needs 50 grams of protein a day, that means the intensive system would cover a person's protein needs for 223 days and the extensive system would cover a person's protein needs for 93 days (if they had no other sources of protein).
That's what I have so far. I still need to run the numbers on surface area required for using duckweed as the only feed source.
* = This is mostly for efficiency purposes. First off, eating lower on the food chain makes most sense from an energy perspective. It also makes sense to use small fish that can be eaten whole because their bones and organs contain valuable micronutrients, while larger fish like catfish or bass may only have an edible weight of 25%. There is a history of American Indians eating shiners and minnows, along with a global history of eating all sorts of small fish (anchovies, sardines, etc). Fathead Minnows seem most suitable to my region and have a rapid growth rate. They can go from egg to ~1.5 inches in 6-8 weeks. This rapid growth rates means I could get 2-3 breeding cycles over the warm months, which dramatically increases my output. There should be much lower risk of microplastics when breeding minnows in a controlled environment compared to capturing them in the wild.
** = With smart design and a pneumatic ejector pump, you actually can use an air pump instead of a water pump. This is much more energy efficient (e.g. a system of this size might only require something like 12 watts of power to continuously pump). See here for a DIY build:
https://www.youtube.com/watch?v=44L6S3DIwfg
Edit: My initial biofilter estimates were off so I found a better formula which says only ~50 gallons of biofilter space would be needed for 60 lbs of fish.
Edit2: I just ran the numbers and I would need something like 37 sqft of grow space for duckweed to feed 60 lbs of fish (assumption is I harvest half each day for feeding and it grows back). The nice thing about this is you only need a few inches of water since duckweed only grows on the surface.