Micro-scale Aquaponics March 21, 2013 17:35

Aquaponics is a portmanteau of aquaculture (the controversial, frequently highly impactful mass cultivation of fish) and hydroponics (the controversial, often chemical and energy-intensive soil-less cultivation of plants).  On paper it seems like a match made in heaven - combining two imperfect systems to address each others' weaknesses and form an elegant, efficient, and sustainable artificial ecosystem of food production. Here's how it works, in my non-expert understanding
  • Fish excrete ammonia into the water as a waste product.  This is toxic and will eventually build up and kill them.  For this reason, water is changed frequently in traditional aquaculture (or in your home fish tank).
  • Certain bacteria love to eat ammonia and turn it into nitrites.  Other bacteria love to eat nitrites and turn them into nitrates.  We will encourage these bacteria to grow on the "media bed," here consisting of lava rock.
  • Nitrates are not toxic to fish, and plants can use them as a nitrogen source.  Hungry plants will suck the nitrates right out of the water.
  • Thus, water changes are rarely required.  No more nasty polluting effluent!
  • Bonus, chemical fertilizers are not required.  Win-win!

Naturally, I decided to build a system.

 2013-01-15 14.52.24
the frame for the grow bed in mid-build.  For reference, it's about 20" (50cm) long

 I have a feeling I may regret this, but in the interest of not taking up too much floor space I decided to build the smallest system possible.  I'd seen some at a friend's place with a small grow bed mounted atop a fish tank - not meant for pumping out masses of vegetables, but perfect for a proof of concept.

 2013-01-15 16.51.04
The grow box lined with polyethylene pond liner.

  That apparatus in the upper right is a bell siphon.  The large, open pipe just holds back the lava rock.  The capped pipe is open on the bottom and fits over a stand pipe.  The idea is to pump water constantly into the box, so that when it reaches a certain level it forms a siphon and drains the entire box.  Then it refills and the cycle continues.  This is a low-cost way to create an ebb-and-flow system that keeps the lava rock wet but gets lots of air distributed throughout.  Here's a nice video that explains how the siphon works: http://www.youtube.com/watch?v=ZHaiVhVZ3kM

 2013-01-15 17.16.58
 The completed box, with the stray edges of the pond liner held down by cedar lathe trim.

 Now a bit more on the lava rock in the grow bed.  It serves two main purposes.  First, it provides a solid structure for plants' roots to grab on to.  Second, all those pores and crevices give it a very high surface area.  This surface provides a home for all those important de-toxifying bacteria.  Also, it doesn't hurt that it's a lot lighter than regular gravel.

 2013-01-23 12.08.06
filling the assembly with water

 Although I seemed to recall seeing a grow bed resting on the top of a fish tank, this box seemed much too heavy for this.  I put this stand together to support it above the tank where the outflow water can return directly to the fish tank.  

 2013-01-23 11.57.00
I had to run a hose all across the store to fill the tank.


 2013-02-27 16.03.56
the bottom of the grow bed

 This is the outflow pipe of the bell siphon.  By lengthening this pipe and changing the shape, it's possible to encourage the siphon to start (a certain amount of back pressure is required).  On the other hand, you may need to shorten the pipe to get the siphon to stop properly.  I fiddled around with this a lot trying to make it work consistently; next time I'll take the advice of more experienced folks and start with a proven design.

 2013-02-07 13.09.08
red wigglers!

 You'll note the system I set up for the store has only two components: a fish tank and a grow bed.  Bacteria on the media convert the toxic ammonia and nitrites, but conventional wisdom holds that a filtration step is required to remove solids (fish turds) from the water.  Wanting to make the system as simple as possible, I've opted for a shortcut outlined in Sylvia Bernstein's Aquaponic Gardening.  She asserts that by using a deeper-than-usual media bed and adding a population of worms, it's possible to capture the solid fish waste and mineralize it without it gumming up the system.  So I tossed in this nice handful of red wigglers from one of our in-store compost bins.

 2013-02-07 13.29.31
Minutes later, the worms had slithered away, out of the light and deep into the bed of lava rock.


 2013-02-27 16.02.45
planting the bed

 Here's the bed with a few seedlings and ornamentals transplanted into it.  Those are radishes in the plastic tray sections on the right; these will probably not be good candidates for this system since the lava rock would impair their bulb formation.  Then again, I'm not sure if anyone's actually tried it.  

 2013-02-27 16.02.59
off to the races!

 The system set up and running.  There's a tilapia in there, but he seemed jumpy so we made a cardboard blind for him to hide in.  That's also the reason for the wire mesh on the top of the tank (weighted down with jugs of castor oil).  

 2013-03-13 10.23.01
A close-up of the lettuce starts we transplanted in.  

 We're experimenting here with several methods of seeding.  Those four coir pellets don't seem to be giving good results - they get and stay soaking wet, perhaps too wet for the young roots.  Next we tried a little scrap of coir mat- that's the grassy-looking stuff at the lower right.  I stuffed some in between the lava rocks and dropped a couple seeds into it.  Looks promising!  

Last, I stuffed some of the seedlings I thinned from the coir directly between the rocks - you can see one of these just above and left of the grassy coir mat.  These seem to be doing well!  I think the roots get the most air this way.  Next up I think we'll try seeding directly into the lava rock - just sprinkle a few seeds in and see what happens.  Boy is this exciting!