Backyard Aquaponics
A place to discuss aquaponics

So I'm currently in this awesome class that is totally centered around generating a design proposal for a brownfield development in a certain large American city (no, not Detroit and no, I don't think I'm supposed to let on to the development particulars). This is a really exciting project because the city government has the will to see the project through to completion (it's massive in scale) but the current proposal is hopelessly flawed.

Enter my working team of a handful of graduate students with various background working for a common purpose. One of our goals is to close the water and nutrient cycles, certainly a daunting task. This development is just outside the downtown of the city so there isn't really an option to spread out (lawns = 0) so in terms of food production, AP is the most efficient way to go. Unfortunately, the only light to be had is on the roof and while I'm a structural engineer and know it could be done, there's no reason to design a roof to hold 50,000 L of water and 100,000 L of gravel when you don't have to.

So here's my basic idea. Enclose virtually the entire roof with a greenhouse and fill it mainly with NFT troughs. It seems like the lightest way to get some decent growth. Above support columns, heavy gravel beds could support plants that have more significant root systems.

Entire development will be popped up one level (~4m) for various reasons (it's a brownfield site afterall) so there's plenty of shared basement space for fish tanks and gravel media. Solids are good, no removal (trying to close the nutrient cycle...) If both the fish tank and the vast majority of gravel media were in a basement, would the critical nutrients be released into the water? seems like they should be. Filtered water is pumped up to roof for nft and a smaller number of gravel beds. Water returns back to fish tanks. Multiple fish tanks would allow for constant harvest, feed rates and effluent demand on gravel media and plant growth.

Also on the roof (must be in greenhouse for temp reasons) are many BSF larvae auto harvesters (very simple devices fed by abundant restaurant scraps) that could drop tasty morsels through shoots directly to fish tank to supplement or replace grain feeding. Composting worms in gravel media also harvested and either fed to fish or sold at market.

Did a quick sketchup if that's totally vague. Main questions are as follows:

What sort of ratios to use between FT (considering many tanks with different size fishes in each), basement media, NFT and rooftop beds?
Is gravel in basement a good idea?
Are there numbers for feed rate per NFT hole?
How much heat gain/loss to water flowing through NFT?

http://sketchup.google.com/3dwarehouse/ ... revstart=0
note:picture lots of these side by side, front to back.

Off to bed now, excited by what morning insights you'll all have.

thoughts:

keeping it all on one level is going to cut your pump power consumption heaps

maybe incorporate a gravel growbed at the start of each batch of say 4 nft runs and autosiphon it into the ntf.

for solids entrapment and breakdown i'd definatly go shallower with greater surface area VS deeper with less surface area. 300mm to 400mm deep.

we'll comment on the suggested amount of gravel based on what Kg of fish you expect to produce an a given 12 months.

WOW, keep us informed on the progress!

If you want to keep weight down, isn't there a different media to gravel? The stuff weighs a ton. I've just started to use the coco coir pictured below, it drains really well and is light.

Having terraced beds would reduce the amount of water (and weight) on the roof.

steve
I think that much of the headloss from raising water could be recouped from falling water, either through power generation or some combined fall/lift system (still draws power of course). I realize this increases power consumption, but that isn't the biggest driver here, it takes a back seat to sunlit space and construction efficiency.

Wouldn't it make more sense to run the nft into the gravel growbeds for height reasons and not the other way around? NFT usually takes continuous flow right? but at what rate? maybe could use that into to decide the ratio for nft : gravel beds on a continuous F&D system that autosiphen back down to the FT. This would also be a good way to keep gravel beds over columns in the building structure as it breaks them up a bit.

Shallower gravel is due to lack of oxygen at deep layers yes? Perhaps perforated pipes could pump (low pressure) air into deeper troughs? That would mean that it couldn't be flooded, a good or bad thing?

For the fish I'm thinking it needs to be trout or other cold water fish, this is a northern city by a big deep lake so it is generally easier to make things cold than hot. Probably get them as fingerlings for this sort of setup and raise them to market.

I'm trying to scale all of this on a sqft basis (or m2 for all of you out there with your head on the right way). That is to say, the system can produce 2.3kg fish + 9.8 kg veggies/sqft(GH)/year at a cost of .30$/sqft/year. Easy that way to combine with consumption stats and market rates. So I'm not looking for a particular number, just a general idea (lots of assumptions included) about what would be reasonable design guidelines.

On the other hand, if they decide to build like this, I suspect they'll be calling me asking how in the hell you get a gravel bed to auto siphon....

Something I took for granted is that the greenhouse space is likely the limiting space location, not the basement.

Here's an idea, most of the flow just circles back and forth between the tank and gravel filter in the basement (low pump costs) and once it's pumped to elevation, it is cycled through a few times on the roof (low pump costs) to extract maximum nutrients and then flow back down and get re nutriented.

Still, can recapture much head lost through something simple like a water wheel.

You would want to run with fairly high nitrates in the FT in this case.

That truly is a far out urban concept. The greenhouse on the roof sounds great. It should especially help keep out any acid rain. It should also help with heat loss since there wont be wind blowing across the nft channels.

If your pipe run is long or exposed to the elements I'd think about insulating it as it could lose alot of heat otherwise. This is what we do for solar thermal installations to keep the heat in.

I have done hydroponics before as well as aquaculture so I know a bit about each of them as separate elements but Aquaponics is a whole new ball game to me.

I do know that having the gravel beds before the nft can be an efficient mechanical filter. Gravel filters work but cleaning them is a b***h and could be restrictive in a basement (where to clean and drain?). Also, as I understand their use in aquaponics, gravel beds are ebb and flow. So as far as a prefilter they wouldn't work in the traditonal sense of aquaponics.
With a constant flow NFT system you would need another reservoir on the roof to be filled intermittently with each flood and drain cycle from the gravel beds. If this was the case you'd need a separate system on the roof that ran by filling the reservoir and having a separate pump move water to the nft channels and be gravity-fed back to the reservoir. With an overflow on the rooftop reservoir every cycle from the ebb and flow beds could overfill the resevoir and drain back down to the tanks. Then you could use planted gravel beds with an ebb and flow cycle in the basement with artificial lighting (check out solar tubes too- wall mounting might be a possibility or even adding windows if it's on a floor above the basement).

If I were you I'd just stick to an efficient mechanical filtration method in the basement that focused on ease of use and cleaning. As this sounds like a commercial scale operation efficiency should be key. I'd look into settling tanks (easily made from 55 gallon barrels or baffles in tanks) as well as using matala mats or japanese mats for mechanical solids filtration. These do work well for koi and I'm using them on my current tilapia tanks along with bioballs in my wet/dry. There are a lot of other mechanical filters that would be appropriate for large scale aquaculture.

As far as getting all the nutrients to your plants you could do foliar spraying for additional nutrients not found in the system water. As I understand it that is the main problem with a fish effluent based system. Alot of nitrogen but not very much of anything else that your tap water doesn't provide. Straight dosing the fish tanks with fertilizers probably aren't a good idea but you'd have to ask the veterans on this site about that.
Another option is a separate reservoir for supplemental dosing. If you had another reservoir you could dose the nft's with the necessary supplemental nutrients and have them drain back to that reservoir. There are electronically controlled valves that we use for solar pool installations called jandy valves. Using these with their controllers and your pumps on timers you could set up a dosing schedule that could have you growing more than just leafy green vegetables or herbs. It would be a simple matter of feeding the nft from the fish tanks then cutting the cycle and feeding from the supplemental reservoir. This would allow for fruiting type vegetables and fruits as well as prevent contaminating the fish water. It would also fit in with an ebb and flow cycle from the fish tanks to the gravel beds and to the nft channels.

I wish you the best of luck as this type of operation is the future of aquaponics in the urban environment. The pioneering spirit is alive and well.

If you go to the GBs first, they'll act as a filter removing solids that would clog up you NFT system.

True but solids are already removed in the basement. There would essentially be three circuits in the system.

1. FT to gravel. For conversion of ammonia to nitrates and breakdown of solids in gravel media. Does the gravel need roots in it to break down solids? Or just worms? Do worms need light?

2. Up/Down circuit. brings nutrient laden water up from basement and takes plant filtered water down to FT.

3. roof circuit. Cycling nft channels continous and gravel beds f&d with basement water till nutrients are low then dumping water down.

L8-
I don't want to filter out the solids because they provide everything that ammonia only water does not. Plus some composting worms in gravel bed should be able to deal with reasonable levels of solids and could be harvested regularly (isn't hard to do). I imagine you have in mind much much high stocking densities than most APers typically use. Limit here isn't tank size or water usage but GH space. Don't want to get too complicated with sprays, regular maintainance etc. looking for as close to kitchen scraps in, veggies and fish out, as possible.

yep, i was saying GB before NFT for solid filtration, but if you are going to have the gravel in the basement then my point is redundant.

my point of surface area to volume of the gravel is from observations of clogging factor of deeper and narrower beds Vs shallower and wider.

ok, basement it is, well if you rust a CHIFT-PIST (but we'll call it CHIFT PIBT) Sump being replaced by Basement , what you can engineer is that your full height of pipe to pump to tank is flooded (think a U tube or manometer) pumping power loss should be limited to frictional only as the suction will have almost the same head as the discharge (or am i missing something?)

worms are fine in the dark
keep it coming

Steve

not missing anything, but i think frictional losses will be big enough reason to keep big up and down pumping to a minimum, especially when it can be reduced by diverting a large amount of filtration flow through the single gravel tank in basement.

I think im starting to zero in on the main question here. I have a given grow area (getting solar radiation) averaged from seedlings to full grown monsters, how much fish food does it take to fertilize that area? Once that question is answered, I think everything else can begin to fall into place.

Basically, I'm looking for the plant centered design. I realize more fish could be added with various filtration, but just in terms of supporting the GH plants, what's the minimum fish food dosing?

I would also look into the added benefits of growing plants and having a greenhouse on the roof. Can it help heat/insulate the building? In Singapore they're growing crops in hydro on rooftops (I realize your climate is different). Besides providing food it helps keep buildings cool and stops reflection onto other buildings.

There are enormous benefits of having lots of vegetation in the city, one of which we remove by putting it all under a greenhouse.

We haven't quite figured out how to deal with storm water retention/reuse. It can get rainy, we'd probably plan for a 4"-6" rainfall. Fish tanks could all take a bit extra with a modified chift or the gravel filters could be flooded for short periods of time. Perhaps flood tanks in the basement would make financial sense.

Then again, stormwater management doesn't necessarily need to be included in this particular system, we could do that elsewhere.

As for the other benefits like filtering air, reducing urban heat island effect (oops, threw a gh on top), increasing insulating capacity, increasing local O2, habitat support and just plain looking pretty....

Sounds like a great project to be working on.

On the greenhouse issue:

As you are obviously aware, opening the plants to the air will have a benefit to the air, but makes the plants vulnerable to specific dangers.

Off the top of my head, the ones that come to mind are damaging winds at high elevation, damaging storms (heavy rain, hail, icing), and temperature loss. I'm sure there are more that are eluding me at the moment.

I think the solution to get the best of both worlds has two parts. The first part is making the greenhouse retractable. Many restaurants where I live have roofed patios that have roll-up heavy plastic sheeting for inclement weather. When the sheeting is down, it act like a greenhouse because the sheeting is transparent. When the sheeting is up, it's open air. These are operated by string, so they seem to be robust.

The second part is wind baffling. On the outer edges of the greenhouse, erect some sort of baffle system to break apart the high winds that would allow the plants to be open air on windy, but otherwise good-weather, days. It could be some sort of plant-based baffle like potted trees, or it could be a mechanical baffle with screens or panels.

Obviously, this kind of solution is not the cheapest when compared to a totally enclosed one. I tend to think that the benefits of hundreds or thousands of reclaimed green space outweigh the initial investment costs though.

Whatever your greenhouse design you'll need ventilation, this means the atmosphere in the vicinity will benefit.

Totally agree. We are looking into some creative financing for the whole operation, essentially socializing the whole farming operation (it's a dirty word right now because of the election but it will pass).

As for the height, it's likely to be a consistent height development--stand on one roof and look out onto all the greenhouses. Wind could best be dealt with by using turbines (smaller ones). As for the coverings, plastic seems the most cost effective and easiest to remove. Nice summers, cold cold winters. Not too worried about making a closed system here, a lot of area to take up (300-450 acres total GH space)

P- I very much agree, various studies have shown that greenroofs reduce ground level ozone and take up NOx. Lots of surface area for particulate matter to collect in also (have to be washed off later...).