Help Designing a Raft/DWC System

[Raymond D. Lewis]

Hi everybody,

 

My name is Raymond and I'm an electrical engineering student. I live in Puerto Rico, pardon my english.  I'm in my last semester and I'm planning to design a aquaponic farm for commercial purpose.  I have skills and experience in 3D CAD software like Solidworks. I'm new to aquaponics but I have read Silvia's book and a lot of many other resource like Murray's videos. I still consider myself a newbie and I would never try to go commercial before running a personal system for at least a year. In my reasearch I had come to the conclusion that for commercial purposes is best to use a raft or deep water culture system.  The main reason behind this is that it is easier to harvest, no need to deal with the tangled roots on growbed media, and it seems to have a better yield (depending the type of plant, of course).  I'm planning to start my system in the roof of  my house.  In Puerto Rico, houses are made mostly of concrete and they tend to get heated by sun.  Setting up and AP on the roof my help lowering the temperature of the house.  The available space that this roof provides is about 2300 sq. feet. I measure it by myself and draw a 3D Model of the roof.  I know that the basic components of a raft system are the fish tank, a bio filter / clarifier and the raceways or artificial channels were the raft or foam is placed with the plants.  A local company that produce food, specially canned food, give-away to me two 1000 liter / 275 gallon IBC that carried FDA Food Garde glue used to seal food cans.  I'm lacking a biofilter / clarifier and the channels.  There is plenty information on DIY bio-filters / clarifiers but I can't find how to make a proper raceway or artificial channel. The information I found tells me that a good starting point is to build them 4 feet wide and 18 inches deep depending the type of plant. Also I haven't found information about ideal plant spacing for specific plants. Is there book or any other resource that can tell me info about the plant and the necesary spacing?

 

I'm a little bit concern about using PVC plastic material and I will try to design this system using HDPE (High Density Poly-Ethylene). For the moment I dont want to argue or discuss about healthy factor of the PVC plastic because I may change my mind later and use PVC. For now I just want to focus on the design of the raceway / artificial channel. For the moment I found pond liners made of HDPE.  I can make the rectangular structure for the raceway and cover it with this liner. What materials should I use for the supporting structure, wood that can rot, metal that can rust? Also I can make the raceway with HDPE barrels cutted in U shape and connect them with HDPE piping. The benefits are that HDPD barrels will not rot or rust and the round shape of the bottom of the channel will provide better dynamic flow avoiding dead-zones, zones with low flow rate. The draw back with the barrel system is that the witdth of the raceway can not be 4 feet, in fact it will be about 2 feet because this is the length of the barrel's diameter.  I can overcome this by designing the system in a zig-zag format, puttting side by side two lines of 2 feet wide raceways / half barrels, both having different flow direction. Another drawback is that since the cutted half barrel is U shape and not rectangular, the plant planted on the sides will not be provided with a depth of 2 feets. Only the ones planted on the middle will get the full depth of two feets. I might start with tomato plants, Puerto Rico lacks high quality tomato. Most of the tomato we produced is exported. I want to start small and provide tomato to the local market. Should I concern about this depth issue? Which system you guys prefer, rectangular or half barrel?  Do you know a better way of making the raceway / artificial channels?

 

I'm planning to do this system semi-automated. I'm working as an IT Specialist in a busy hotel and don't have much time to monitor myself the starting system. I know this is a critical step to ensure that the system can cycle properly and is not the best way to start but this is how real life works :( . The plan is to  develop a control system that can monitor water temperature, dissolve oxygen, PH, ammonia, nitrite and nitrate.  Also the system will send me a SMS / text message if something goes wrong.  Then I'll be able to log in via my cellphone web browser and manually issue commands, based on the sensor reading, like adding small ammount of buffer to stabilize PH or removing water and refilling it with pure fresh water to lower ammoniun, etc. Also I'll be able to manually feed the fishes remotely watching them through a IP camera and controlling the feeder through my smartphone. The funny thing is that for me it is easier to design and develop this complex automated system than to design and develop the AP itself. LOL.

 

 I really appreciate any suggestion and I'm willing to help anyone with my engineering knowledge. Thank you so much!!!!

[Jonathan Kadish NYC AA Chair]

Being that you are down in PR hop on over to the University of the Virgin Islands and take their commercial aquaponics course. The DWC system there was developed by Dr James Rakocy and has been perfected over the last 30 years. You can get a lot of advice from a lot of people that will point you many different directions...so  why not go to the source.

[TCLynx]

If you don't have time to be there to set up and cycle the system, how will you have time to work the bugs out of the high tech monitoring stuff if you can be there to do comparison tests to make sure you are getting accurate readings?  Or fine tune the camera's, buffering, and feeding mechanisms or net out dead fish?  Now I'm not sure how you will really start up a system and run it without having time to be there in person since with raft systems you need to regularly plant and harvest the rafts and I really don't see that as a completely automate-able task on a home scale.  On a commercial scale, the planting and harvesting is probably the most time consuming part.

You may be over thinking the high tech commercial set up by trying to design it before you even set up and cycle up your first backyard system.

As for how to build the troughs for a raft system.  I would say the Durascrim or other HDPE liner is good.  I would either support it using metal conduit (like they use for hoop houses) framework or do concrete block or other concrete trough.  Of course if you do concrete trough, you could do the epoxy paint to seal it instead of liner.

I do not recommend the barrels for your troughs since you then loose the ability to float the rafts from one end to the other which is one of the main benefits.  Also the center of the barrel trough would only be 1 foot deep at the deepest.  And the barrels would require you to build supports to keep the barrels from bowing and bulging so no savings and all the added plumbing fittings to hook barrels together with large enough HDPE pipe to keep the flow good is going to be very costly.

[Raymond D. Lewis]

Thanks for the advice but hurracaine season already started and they will not offer the course until next year.

 Jonathan Kadish said:

Being that you are down in PR hop on over to the University of the Virgin Islands and take their commercial aquaponics course. The DWC system there was developed by Dr James Rakocy and has been perfected over the last 30 years. You can get a lot of advice from a lot of people that will point you many different directions...so  why not go to the source.

[Raymond D. Lewis]

I still have the weekends and holidays.  My brother might help me too. He is a student and he is unemployed. As for the raft setup, I can't use concrete, water itself weights a lot and I don't want to add additional weight to my roof. I don't understand how one can build a channel with conduits and a liner.  What will happen to the liner between the spaces that are between the conduits? Will the conduit rust because of our high humididty (around 60% to 80% all year)? I guess I can paint or treat the conduits to protect them from rust.  Do you know a good supplier of HDPE Liners?  I really appreciate your help, thanks a lot. 
 
TCLynx said:

If you don't have time to be there to set up and cycle the system, how will you have time to work the bugs out of the high tech monitoring stuff if you can be there to do comparison tests to make sure you are getting accurate readings?  Or fine tune the camera's, buffering,....

[Jonathan Kadish NYC AA Chair]

Too bad about the UVI season ending. There are others in Florida doing a great job of education for DWC systems. Aquatic Eco Systems or Green Acres Organics are experts and will show you everything you need to know as well as get you some hands on experience.

[Raymond D. Lewis]

I did my homework and it seems the right path to go is using Dura-Skrim® 20WW. It is UV stabilized, safe becuase its made of low density polyethylene, it is strong and durable becuase it has a metal mesh/frame between the two layer of LDPE.  I hope it can last more than 10 years.  I still don't know what material use for the supporting structure.  Puerto Rico has high humidity, the channels will be place on my roof so they will be open to the enviroment (rain, sun, wind, ...).  I can't use wood becuase, if they get wet or moisture, they will rot. I can't use metal, except stainless steel but is too expensive, becuase it will rust. Concrete is to heavy.  What about the best of both worlds, wood + concrete?  Maybe I can use concrete fiber like plycem/duramax, right?  Any idea will be appreciated. Thanks.

[TCLynx]

I've made troughs using snap clamps and the chain link fence top rail type conduit.  I wonder If I can find a picture of it for you. So the two white troughs under towers are made using the conduit and snap clamps along with the durascrim liner.  The conduit is galvanized to help protect it from the elements and you should add some extra paint or other protectant to the cut ends or where ever you see rust starting to form.  I live in Florida and we have high humidity here too and I've had problems with wood an liner so I don't use them together anymore because of termites and carpenter ants.  Unfortunately, if you can't use any building materials because they are all unacceptable for one reason or another, then it will be very difficult to build anything.  You will eventually need to decide on the least problematic building material for your situation.

[Raymond D. Lewis]

Thanks for showing me how the conduits and the liner works together. I know have a clear idea. Your troughs are narrow and I can see this setup works pefectly because the edges are so close and the bottom of the liner rest on the floor so that the liner can withstand the weight of the water.  Do you think that the Dura-Skrim liner can hold water from a 4 feet wide troughs and the bottom of the channel in the air at waist level? Also, what do you think about  concrete fiber, like plycem/duramax, for the structure of the troughs? Thanks.
 
TCLynx said:

I've made troughs using snap clamps and the chain link fence top rail type conduit.  I wonder If I can find a picture....

[TCLynx]

You can go 4' wide troughs with the durascrim and conduit but you want to have the bottom of the trough resting on the roof or ground or whatever.  I have done a trough with the durascrim up at waste level but you then need to provide support under the liner as well as more framework for support which will add to cost.  Having the trough as the lower point in the system so it is resting on the roof will also spread the weight of the water over more surface making it far more reasonable from an engineering point of view.

Please make sure the roof of the structure can support the weight of tanks and water and all that, it is heavy.

I don't know anything about those concrete fibers.

[Jon Nose]

consider using bamboo...?

[Raymond D. Lewis]

I really want to have the troughs at waist level because it will be easier and more efficient to work with.  As soon as I finish a preliminary trough design I will calculate its weight to make sure my roof can handle it. What do you think of using PVC panels for the support of the Durascrim?  The liner will protect the water from contaminating with the PVC.  PVC will last forever and will not rot, rust or get termites. I haven't check the cost yet, but last year I was offered to use it instead of wood panels for a NASA project I'm still working (Helmholtz Cage, or 3D Magnetic Field Simulator. The guy at the FAB LAB told me that the price from wood to PVC didn't vary much.  Thanks again for you ideas.

 TCLynx said:

You can go 4' wide troughs with the durascrim and conduit but you want to have the bottom of the trough resting on the roof or ground...

[Raymond D. Lewis]

I haven't though about bamboo.  I might be able to get those trees for free.  They are everywhere in Puerto Rico.  Bamboo is still susceptible to get rot and termites. Does anybody here has worked with bamboo?

Not a bad idea. I'll think about it. Thanks.
 
Jon Nose said:

consider using bamboo...?