Aquaponic System Final Design

I thought it’s about time to get down to business. So, I’m going to devote the month of June and probably a bit of July to building the first unit of what I hope will be many more units to come. This post is meant to be an overview of the system so that any aquaponically-inclined readers may warn me of potential catastrophe.

The University of the Virgin Islands' Aquaponic System

Aquaponics– An Overview

Aquaponics is the combined culture of fish and plants in recirculating systems. Nutrients, which are excreted directly by the fish or generated by the microbial breakdown of organic wastes, are absorbed by plants cultured hydroponically (without soil). Fish feed provides most of the nutrients required for plant growth. As the aquaculture effluent flows through the hydroponic component of the recirculating system, fish waste metabolites are removed by nitrification and direct uptake by the plants, thereby treating the water, which flows back to the fish-rearing component for reuse.  In my system tilapia will be produced along with a variety of herbs, leafy plants, vegetables, and perhaps fruits.

The aquaponic system I will be utilizing is a scaled down version of the University of the Virgin Islands commercial scale system. It is roughly 1/4th the size of the UVI system, but may be multiplied in accordance with resources and demand.

The UVI system has been producing tilapia for more than a decade. It is a proven system and detailed information relating to it is freely available, including some of this text which I am, honestly,  guilty of plagiarizing freely at times. Thank you Dr. Rakocy. I wish I could afford to go to the Virgin Islands and take part in one of your training programs, but I’ve got to do it the hard way.

Aquaponics has several advantages over other recirculating aquaculture systems and hydroponic systems that use inorganic nutrients solutions. The hydroponic component serves as a bio-filter, and therefore a separate bio-filter is not needed as in other recirculating systems. Aquaponic systems have the only bio-filter that generates income, which is obtained from the sale of hydroponic produce such as vegetables, herbs, and flowers. In the UVI system, which I copy, and which employs raft hydroponics, only calcium, potassium and iron are supplemented. The nutrients provided by the fish would normally be discharged and could contribute to pollution. Removal of nutrients by plants prolongs water use and minimizes discharge. Aquaponic systems require less water quality monitoring than individual recirculating systems for fish or hydroponic plant production. Aquaponics increases profit potential due to free nutrients for plants, lower water requirements, elimination of a separate bio-filter, less water quality monitoring and shared costs for  operation and infrastructure.

The Wrong Way Farm Stay Design

This is roughly what it will look like though I've made a few changes (see below).

(Note: My design has changed slightly over two months since I made this post, so see this post for more information). My design is meant to get the same results or better than the UVI system but at a much less expensive initial cost. In some ways it is more complicated because I will be trying to control the environment with what I think is a pretty cool greenhouse design and making use of passive solar energy for water heating. It will also use less energy despite its need for climate control.

This is the final (I hope) layout to the aquaponic system.

So, here’s the floor plan. As you can see, it is 22.4m long and 6.55m wide. Some system details are as follows:

  • Rearing Tank — The rearing tank will hold roughly 9.5m3 of water. I rounded the ends so the stupid fish don’t get bloody noses all the time. The tank will be stocked every 4 weeks with 120 fish. There will be 6 cohorts of fish aged 4 weeks apart at all times. I will separate the cohorts with suitably sized netting. The position of these divisions will be adjustable in accordance with the growth rate of any given cohort. Harvesting will be done weekly, 30 fish at a time. The outside of the tank facing south will be painted black and exposed to the sun.
  • Hydroponic Tanks — There will be 4 hydroponic tanks. Each will be 12m long and 1.2 meters wide. At a water depth of 30cm, each tank will hold roughly 4.32m3. Plants will be put in net pots which are inserted into holes in Styrofoam boards (1.2m x 0.6m) and dangle their roots happily in the nutrient rich water.
  • Clarifier/Filter/Degassing Units — Each hydroponic tank will get its own set of these highly important if simply designed contraptions. A clarifier, otherwise known as a swirl filter and other such names, removes the lumpier pieces of fish waste. I intend to use 200l plastic barrels. The filter is just another smaller barrel that’s got an armload of orchard netting in it to which the finer solids will be instructed to attach themselves in an orderly fashion.  The degassing tank is another small barrel with a few air stones in it to help remove carbon dioxide, methane, and such.
  • Pump — I’ve purchased a Reef Octopus recirculation pump which will push 7,000l per hour while consuming a frugal 88W. This is roughly 1/4 of the flow rate that the UVI system uses.
  • Air Pumps — I’ve purchased 5 Hailea air pumps. Each would push 60l of air if only I were at sea level instead of 1,200m. They are also frugal, using 55W each. Each hydroponic tank will have its own air pump. Ten of the 12 diffusion nozzles fitted to an air pump will go to air stones spaced equally along the bottom of the respective hydroponic tank. The other two will be fed to the degassing tank. The 5th air pump will be devoted to keeping the fish bubbly and happy.
  • Sump — The sump is just a 1.2m round concrete ring set in the ground at a lower height than the rest of the system. The pump will reside here and replace the water that has flowed by gravity from the rearing tanks through the other system components.  There will be certain losses due to evaporation, plant uptake, leaks, etc. Depending on the water temperature, this loss will be replaced by either hot water produced in a solar water heater (a nice name for a couple of 200l barrels painted black, facing the sun, and enclosed/insulated) or ambient temperature water from a rain barrel. This is also the place where additives such as hydrated lime are gradually added if necessary to raise the PH.
  • Total Water Volume — About 30m3
  • Total Growing Area — 55 to 57.6m2
  • Greenhouse Footprint — 147m2

Tilapia from Nam Sai Farms, my future fish fry supplier.

Strategy– The Fish

Tasty as they may be, the tilapia are in the tank to eat, pee, and poo. In fact, they will be expected to consume between 3,978 and 4,099g of high quality pelleted food a day. At least those are the numbers I get when I apply the data from Nam Sai Farms’ trials on fish growth and feeding rates to 6 cohorts of 120 fish stocked 4 weeks apart. This very slight variation in feed input is the result of harvesting 1 cohort during a 4 week period, or 30 fish a week. Why such an emphasis on feed rate? Because, as Dr. Rakocy puts it, “In a correctly designed and balanced aquaponic system, the ratio between fish and plants is based on the feeding rate ratio. The feeding rate ratio is the amount of feed fed to the fish daily per square meter of plant growing area. For a raft hydroponic system, the optimum ratio varies from 60 to 100g/m2/day.” Assuming that I utilize about 55m2 of growing area (one of my tanks has to be less than 12m long because the liner comes in 50m rolls, something I just realized), that’s about 73g/m2/day.

If I were to begin stocking fry of an average weight of 27.5g on Saturday, August 4, I would begin to harvest them on Saturday, December 29, at which point they would weight and average of 717g. The 30 fish harvested each of the following 3 weeks would weigh 767g, 817g, and 867g, respectively. This is also the period when the hydroponic component would be in full operation.

But I’m not going to do it exactly like that. The minimum order for fry is 1,000, so I’m going to chuck in the whole lot at first. According to my calculations, after 6 weeks the average weight would be 138g and they would be consuming 3,660g of feed a day. At 67g/m2/day, that’s plenty for full plant production. But, what about after that? Well, at less than 200g I doubt I could sell the extra tilapia, so I’ll gradually stock my river with them, keeping the feeding rate in the rearing tank as constant as possible. That means I’ll be harvesting plants in full from around the first week in October.

Tilapia fry (all males) will be sent to me by bus from Nam Sai Farms. They average about 0.25g and are about 1″ in length. I will “nurse” them to a more robust size in Ubon. My close-to 8-year old daughter, Megan, will manage the operation under the stewardship of her aunt while her mother, initially, anyway, incessantly complains. The nursery will be a miniature aquaponic unit. I foresee it supplying all the veggies year round for Wrong Way Cafe. More about this later.

Strategy — The Plants

The somewhat exotic "Red Oak" variety of lettuce.

Salad lettuce is the preferred plant in raft systems, although almost anything will grow. Lettuce is very expensive right now. In fact, the other day at a market in Vientiane I could hardly find any, and what I found was a poor excuse for lettuce. Initially, I will devote 3 of my 4 hydroponic tanks to lettuce production. Two of the 3 types of lettuce will be fairly standard local varieties and the 3rd will be the somewhat exotic “Red Oak” variety. These will be nursed from seed for 2 weeks then embark on a 3 week journey from one end of a hydroponic tank to the other. Each hydroponic tank can produce 80 robust heads of lettuce a week for a total weekly harvest of 240 heads. The 4th hydroponic tank will be devoted to a variety of other plants, namely cilantro, water convolvulus, and cabbage. Cilantro is another plant that is very expensive at the moment, and usually expensive. The goal of greenhouse production is to time the crops to when outdoor conditions are not favorable, so what I grow may vary with the seasons.

The plants will be sprayed once a week with “worm tea.” My hope is that this will provide them with some of the trace nutrients difficult to come by in an aquaponic system. Iron is one such example. It also protects the plants from harmful insects, but I’m hoping insect netting will perform this task suitably. Other than that, I don’t foresee a lot of work in the plant department. There’s no weeding to be done, no watering, no cleaning. The Styrofoam boards are lifted off the far end, the plants removed, and young plants are added at the front end, once a week. The labor will be in the fish department. This includes feeding them 3 times a day, keeping accurate records of consumption, routine emptying of solids from the clarifers (probably 3 times a day), and periodic rinsing of the orchard netting in the filter barrels. Some of the labor will pay for itself, such as applying the solids removed from the clarifiers to my coffee trees– higher yield.

Biodiversity

Giant freshwater prawns add to the biodiversity of the system.

As any of you serious aquaponic guys or gals who are familiar with the UVI system may have noticed, my system falls a bit short in terms of aeration. I hope to make up for this by splashing the return water from the sump into the rearing tank. In the hydroponic tanks, I’m contemplating a secret weapon– freshwater prawns. These fellows consume detritus, agitate the water, and are otherwise beneficial to the roots of the plants. They are also very tasty. At a stocking density of 3 to 4 prawns per square meter, I estimate an annual harvest of roughly 75kg. They will be tricky to harvest, though.

Dollars and Sense

Japanese raccoon dogs (tanuki).

There is a Japanese saying which goes something like “Counting the raccoon dog (tanuki) skins before you’ve caught any.” That’s what I’m about to do. But, hey, that’s part of the fun. So, here I go.

  • Fish Yield over 4 Weeks (28 Days) — This will be about 95kg. Tilapia are moderately expensive in Laos, and especially on the Bolaven Plateau as they normally need to be trucked up from warmer climates. They can probably be sold for 20,000 kip per kilogram ($2.40), or 1.9 million kip ($228) over 4 weeks.
  • Lettuce Yield over 4 Weeks (28 Days) — Although I will begin by using 3 of the 4 hydroponic tanks for lettuce, I’ll use all 4 for this calculation as the value of what’s grown in the 4th tank is likely to be in the same ballpark. At the moment a head of lettuce is worth about 10,000 kip ($1.20), and the system’s potential is 312 heads every week, or 1,248 over a 4 week period. So that’s a nifty 12.48 million kip ($1,498).
  • Freshwater Prawn Yield over 4 Weeks (28 days) — Catching these little fellows will probably be tedious, so I’m tentatively looking at 1 harvest every 4 weeks. That’s about 5.77kg. They can fetch 80,000 kip ($9.60) per kilogram, so that’s a modest 461,600 kip ($55) at 4 week intervals.
  • Major Cost #1: Fish Feed — I’ll be smuggling the quality fish feed in from Thailand. Tentatively I’ll use $1 per kilogram of fish feed. At an average of 4kg per day, That’s 4$ a day, or $128 at 4 weeks.
  • Major Cost #2: Labor — I want to split the labor between 2 people, not including myself. They can work out a schedule amongst themselves. The total cost I’m looking at is 1 million kip ($120).
  • Major Cost #3: Screw-ups — My electricity is virtually free (hydropower) and I’m not considering depreciation at the moment. So I’ll use a flat 20% for losses and costs that were not considered.

Total yields over a year are $2,964 for fish, $19,474 for plants, and $715 for freshwater prawns. Grand total is $23,153. Less fish feed at $1,664, labor at $1,440, and screw-ups at $4,631, I’m looking at $15,418 net for a year, or $1,285 net a month.  That’s pretty good for an operation in Laos. Four of these units would give me over $60,000 a year. That’s quite a few raccoon dog skins I’m counting. . .

And, so, in closing, here is some absolutely useless information to store along with other useless information we’ve all picked up over the years. The Japanese raccoon dog, or tanuki as it is known there, is famous for the immenseness of its balls (male tanuki, that is).  These over-sized testicles symbolize financial luck. There is even a popular schoolyard song about them, sung to the American Baptist hymn called “Shall We Gather at the River?”

“Tan-tan-tan” tanuki’s bollocks ring

The wind stops blowing

But they swing, swing swing

This entry was posted in Aquaponics, Construction. Bookmark the permalink.

3 Responses to Aquaponic System Final Design

  1. Phibun Mike says:

    Looks good Richard. I have two observations:

    1) Your use of the term ‘cohorts’ is really cool;

    2) Don’t you find the term ‘Wrong Way Design’ slightly unsettling?

    To help with your planning, put me down for 0.64 heads of Red Oak every 27.3 days.

    Cheers,
    Mike

  2. Josh says:

    Richard, thank you for the great information and design ideas. I am traveling now, but intend to take my dining room aquaponics experiment full scale this summer when I return home. I would love to add you to my contacts to bail me out and set me straight when I screw it up.

    P.S. I could not help but read most of your story as if it were narrated by John Cleese.

  3. Scott says:

    How s the year going? Did your projections prove realistic? Are you making the coon dog skins you thought you would be?

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>