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Is Integrating Media Beds with DWC Worth It?

Integrating a media bed with a DWC or raft type system has a multitude of benefits.  One mustn’t only consider the increased growing diversity, but the additional nutrient availability, the addition of a tremendous biofilter, the reduction of labor from not removing solids and the benefit of utilizing those solids.  Of course if this is to be considered for a commercial application, the additional cost of integrating a media bed must be considered as it will obviously incur a somewhat larger price tag then a DWC system alone.   However the gain of integrating the two types of systems easily justifies the increased build cost.

Deep water culture or raft type culture undoubtedly has it’s benefits in commercial type growing ventures.  It can produce certain crops with relatively less labor then a media system; however the market is a tremendous consideration if DWC alone is going to be sufficient.  Monocropping or growing thousands of pounds of lettuce for large grocers or big box stores demands highly efficient growing systems where large, almost automated type production is paramount.  How many aquaponic ventures intend to monocrop lettuce though?  Or do they intend to thrive as a small family farm catering and bolstering a local economy.  If a market is secured that is linked to a local community and catering to local restaurants and chefs, farmers markets, health food stores and buying clubs then all of these outlets demand one common denominator, product diversity.  Therein lies the problem with DWC by itself.

Crops of the woody variety, peppers, eggplants, large producer tomatoes and even spinach tend not to perform well in raft culture.  That is just a few examples and there are several others that rafts can just not support because of the root structure needing something more substantive to grab hold of and they also require higher levels of potassium and phosphorus than a DWC system can supply.  There is also the concern that a media system would incur greater labor inputs with planting and therefore not making media conducive for high volume turn over.  That is absolutely correct, but only for high volume turn-over plants such as lettuce.  With a hybridized system developed to optimize growing diversity, one would never plant lettuces that would be harvested out in three to four weeks into the media bed.  For that matter, any plants that are expected to have a relatively short span in the system would be kept in the rafts where planting is simple and can be facilitated in a highly effective manner right from the proximity of a seedling area.  Labor would place lettuce and other comparable type seedlings into rafts and merrily float them down the deep water troughs where they will live out their relatively short life in the system.  Whereas, producer type plants that would be expected to have a dramatically longer life span in the aquaponic system would be planted into the media bed eliminating the concern that planting in this type of system is too labor intensive as it is only actually done a fraction of the time.  Harvesting would then include picking fruits and vegetables over a long time span and therefore not have any greater labor impact.  Also, the time spent disposing of used media and the washing of net pots is also eliminated.

Nutrient availability from the additional mineralization is another tremendous asset of this type of system integration.   The inherent nature of media bed systems is that they support greater levels of the minerals that fruiting plants require to be productive such as potassium, phosphorus and calcium from the mineralization that occurs from the utilization of the solid waste.  There is  typically little to no provision for the same type of mineralization in DWC alone.  This additional mineralization will also aid in maintaining much lower stocking densities.   This can be incredibly important if the fish commodity does not bring a good return, as it may necessitate maintaining lower stocking densities.  Then the objective is to maintain as little fish as possible, minimizing the associated costs while optimizing plant growth.  It’s a simple equation; less in, more out.  The expenses associated with cultivating the fish/fertilizer generating side can be significant in feed and electric inputs for large populations.  Optimally then, an efficient farm will operate on the ratio that allows maximum plant growth with as little fish as possible and view the fish as nothing more than an occasional treat at dinner time for the farmer and the cost of producing his primary stream of revenue, the produce.

When considering added value to the actual system operation, there is the elimination of the cleaning and removal of the solids from a settling tank.  Anyone that has ever had to remove solids from a settling tank will probably agree that it is the least likeable part of operating a large system.  Removing these solids often is essential, as even at low densities, the buildup of solids over time in these systems is problematic on various levels.  Depending then on system size, fish density, feed ratios and efficiency of the solids tanks, these systems must be cleaned anywhere from daily to weekly or bi-weekly and can take from a few hours to the better part of a day.  Long term thriving media beds with red worm populations have shown to operate upwards of 4 to 5 years before requiring any cleaning.  Weekly as opposed to once every 4 to 5 years is a huge labor savings and a tremendous plus for overall operator happiness!  Besides why would anyone want to remove such a valuable part of the system?

Perhaps the most important consideration for the business owner is the additional cost of including the media bed as opposed to the lesser cost of just a DWC build out.  Is it worth the additional investment?  If you were to consider the same size media bed and DWC setups side by side, the numbers could easily scare any investor, however that is not the nature of the integrated system.   What must be considered is the additional costs to include a media bed with a DWC set up.   It will obviously be more then the comparative cost of a DWC system alone, but in order to make a fair and reasonable comparison, only certain factors should be included.  Both systems will have the costs associated with the infrastructure of the bed itself, regardless if it is DWC or media, so those factors should not be part of the equation. The differences therefore lie in two places, the additional cost of the construction to support the media bed weight and the cost of the media itself.  However, don’t forget to remove the substantial cost of the raft material from the equation and the airlines, diffusers, net pots and growing media which is actually an ongoing expense in the comparative raft trough.  When the costs are realistically and accurately compared, the media bed cost is only slightly more.  For example, the additional cost to build an integrated system that would include 200sqft of media bed and 800sqft of DWC would only be $2800 more than constructing a comparable 1000sqft DWC system.  This is merely a 17% increase and it is calculated with the most expensive media available, so that additional cost could be as much as $800-1000 less depending on the type of media selected.

This additional cost of anywhere from $1800 to $2800 more to build an integrated media/DWC system will easily be worth this investment based upon the ability to efficiently grow crops such as large heirloom tomatoes or red, orange or yellow bell peppers or heirloom striped eggplant.    Even when in season, these tasty veggies and fruits bring a premium price and require no processing or special packaging.  Of course a DWC system may be able to grow these things, but when growing commercially, the goal is optimization and integrating a media bed optimizes so many aspects for the small family farm, the slight increase in initial investment is well worth it.

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Comment by Pices on December 21, 2011 at 3:30pm

Has anyone found a reliable and reasonably cheap sequencing valve and controller to sequentially fill multiple media beds?

Comment by Chris Smith on December 21, 2011 at 2:04pm

Ryan, have you had salts buildup in your aquaponic system?

I have to disagree that tomatoes and other woody crops do not preform well in DWC. These long term crops need special attention but can work very well. Spinach is hard for me to grow in general probably due to temperature.On a commercial level it does not make sense to tie up the mobility of rafts. Growing long term crops simply reduces the potential crop turn over that the raft system offers due to its mobility.

There is plenty of nutrient for tomatoes and lettuce to grow side by side.I have lettuce growing in troughs on either side of the tomatoes. I still have no nutrient drop from the beginning of trough and the end of trough 4 despite the heavy nutrient users in the middle. I am purposely tying up trough space with long term crops to lessen the labor for my workers(my pregnant wife and her sister) and to prove a point.

Averan you are correct on scaling of media beds. Large beds use a large volume of water on the flood cycle. No matter the method of flooding and draining the volume for the flood has to come from somewhere, usually a sump. By using many smaller beds the water usage can be minimized by having sequenced flooding and draining. Sequencing beds so one is filling while another is draining will help to keep the sump size smaller. If running large beds using auto siphons the sump would need to be large enough for the flooding of all beds simultaneously as well as the needs of the rest of the system. Smaller beds allow for easier crop rotation and easy to isolate if needed. I now design my beds so that I can get into the drainpipe from the outside of the bed to clean-out roots when they begin to slow the water flow.

Comment by Gina Cavaliero on December 21, 2011 at 11:42am

I too have looked at multiple feed labels and have found both the menadione sodium bislulfate complex on one and sodium selenite and sodium sulphate on a couple others.  The menadione sodium bisulfate complex is synthetic version of Potassium and has low concentrations of sodium and is actually a highly contested ingredient in pet food.   The selenite and sulphate are both salt complexes, however all were more than half way down the list which indicate they are not in high concentrations.  I understand that it is being introduced to the system and maybe could potentially build up in a large system, however I don't think it will be problematic with certain safeguards in place, ie. proper sizing, multiple beds, etc. as well as micro-organism consumption and plant absorption.  I too have never  heard of this being an issue with salt build ups in media beds operated over very long periods of time.

Of course there may be issues and or complications in adding media beds to DWC commercial operations, but just because there may be issues that will need to be resolved it is no reason to not integrate hybrid growing methods.  Ryan, in reference to your statement that "I also think when it gets down to it, many people will end up skimping on the number of beds needed to save money and set them selfs up for failure."  perhaps some will "skimp" however if they enter into a commercial operation or any business venture for that matter with that philosophy, they are likely going to fail on multiple levels.  Again though to not do something because somebody may do it wrong seems to me as no reason to not advance this technology and we can at least hope to learn from these failures.    

Regarding productivity of media vs raft for certain plants, I guess we will just have to agree to disagree Ryan.  Again, I stated "better growth" and so far my research to date indicates that growth is faster and more productive in media beds then rafts.  We are in the process of doing much more research and when we have amassed a suitable amount of data, I will be more than happy to share it with you, even if the data doesn't support what we have found to be true so far.  So, as I said before, based on my opinion and what research to date has indicated, certain crops will grow better in a media bed than a raft and therefore it comes down to optimization when growing commercially.  

Comment by Sylvia Bernstein on December 21, 2011 at 9:39am

Just to chime in on the sodium buildup question, while this is a big issue in hydroponics I have never heard of it as an issue in aquaponics, nor have I experienced any such thing in my media beds.  I think the reason for this may be that a mature aquaponics media bed ends up closer to an organic soil garden bed than a hydroponic bed because there is so much biology happening there breaking down toxic buildups.  Also, I don't know how much sodium could even be introduced.  I looked at the labels for several fish feeds and only found reference to sodium in one ingredient, mid-way down on a list - "menadione sodium bisulfate complex".  No idea what this is, but since it is a "bisulfate complex" it is probably that sodium might only be a small % of it.  Anyone have any idea?

Comment by Averan on December 20, 2011 at 9:39am

I'm trying to solve this potential issue by adding a super-aerobic fluidized bio-digester and a swirl filter between the media beds and my NFT or DWC.  These two units (in my smallish system) would have bottom drains that go right back into the sump/media bed.  My theory is that the normal solids that most folks collect are simply wastes that have not been given a second chance to break down and be converted into usable nutrient.

I do understand the potential issue of salts/minerals concentrating over time, but I have yet to hear of anyone actually having run into such a problem.  That might be because most folks drain or remove solids regularly, effectively taking out a big chunk of salts such that the levels never become a problem, but then again, it might just be because the plants and micro-organisms are consuming and using them.

Regarding Ryan's issues with scale: Even a large commercial operation should take heed of scale and when they need to scale up production they shouldn't simply make every component larger, but rather add more modules.  This means you don't need to make a giant media bed, you can make 3 medium ones, or 5 small ones, or whatever makes practical, logistical and biological sense.

Besides, you could always just plug an extra drain valve into the bottom of a media bed and do a regular purge of collected fermenting solids.  There are a zillion ways to perfect media beds to make them easy and practical for commercial operations, we just need to put our minds to the task.  ;)

Comment by Ryan Chatterson on December 20, 2011 at 8:10am
"Crops of the woody variety, peppers, eggplants, large producer tomatoes and even spinach tend not to perform well in raft culture. That is just a few examples and there are several others that rafts can just not support because of the root structure needing something more substantive to grab hold of and they also require higher levels of potassium and phosphorus than a DWC system can supply. "

And Gina this is what I was referencing when mentioning that I don't have problems growing those varieties in rafts. To me, "does not perform well, doesnt have the needed nutrients for growth" isnt really the same as "isnt as efficient of a use of space when growing in a raft".
Comment by Ryan Chatterson on December 20, 2011 at 8:05am
The "Ticking time bomb" is the build up of solids leading to anerobic zones in the media bed. I know what you are going to say Rupe
"But if sized properly there wont be build up"
True, but on a commercial scale you're talking massive amounts of space for the beds, massive amounts of media to fill those and with all of the costs related, it seems like a much longer pay off (at least in my location) then other methods. I also think when it gets down to it, many people will end up skimping on the number of beds needed to save money and set them selfs up for failure.

As for salt build up, with zero discharge salts DO build up. It's in the fish feed and there really isnt anything you can do about it. If you are regularly removing solids and topping off with clean water it does a good job of keeping the salinity in check but if you discharge nothing, it's going to build.
Comment by Chris Smith on December 16, 2011 at 9:48am

I have come similar conclusions as you Gina. I found that in my location I can actually build media beds cheaper than DWC. I can do media cheaper because of my location. I live on a volcano and cinder is cheep here. Blue foam now costs $60 a sheet  at the big box store. For the same $60 I can get a cubic yard of cinder delivered to the farm.

For the structure of supporting the media beds off the ground I use recycled shipping pallets. Pallets are free and readily available in most places. I use 4x8 pallets for the table and cut the smaller ones down for the legs. Some of them are made with hard woods like oak and I seek out these. I treat them with wood preservative to prevent the termites and then paint.

Long term crops can be grown in rafts but will eliminate the biggest benefit of DWC. The mobility of rafts can save massive amounts of labor by simply placing newly planted rafts at one end of the trough and harvesting from the opposite end next to a processing area. Floating plants are very easy to move down the line. Long term plants reduces this mobility. For a commercial farm efficiency saves time which = money. It just does not make sense to tie up the mobility and efficiency of rafts with long term crops on a commercial level.

Comment by Gina Cavaliero on December 16, 2011 at 5:22am

Hi Ryan, it is true that things such as eggplant and peppers will grow in a raft system and I did not say that they wouldn't and regardless of where they are being grown, they still require support.   However, it is about optimizing space and growth and cultivating plants where they will grow best when you are growing commercially.  For example, just because certain herbs will thrive in a raft system, it does not make sense to tie up a significant amount of raft space for 3 months waiting for them to reach a size where they will produce a consistent yield when the same raft space would have turned over lettuce three times.  

Also, what Rupert said:

Ryan, what do you see as the "ticking time bomb" in relation to media beds...

And exactly what "salt" buildups do you refer to.. and how are they related to removal of solids, or otherwise??

I am aware of salt buildup issues with hydroponics, but what are you referring to in ap?  Please elaborate!

Comment by RupertofOZ on December 15, 2011 at 7:30pm

Ryan, what do you see as the "ticking time bomb" in relation to media beds...


And exactly what "salt" buildups do you refer to.. and how are they related to removal of solids, or otherwise??

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