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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 Michael Carlsen on February 19, 2014 at 8:34am

You rock Gina!

Comment by Chris Smith on December 24, 2011 at 10:46am

Thanks Rupert. I believe TCL is a distributor for this or a similar valve.

Comment by Gina Cavaliero on December 23, 2011 at 2:28pm

I did exactly that and was thinking Potassium when I a saw K.  Thanks for the correction Rupert. 

Comment by RupertofOZ on December 23, 2011 at 1:45pm

Not sure who distributes to Hawaii Chris... TCL would probably know...

Here's a pic of the valve...

 

If you want any info or flash files of how it works... email me...

Comment by Chris Smith on December 23, 2011 at 1:13pm

Rupert, can you give us a link to the aquaponics valve you refer to?

Comment by RupertofOZ on December 23, 2011 at 12:08pm

Having said all that below... incorporating media beds into a commercial operation.. the grow beds would IMO.. benefit from a period where by they are periodically left "fallow".. primarily to allow for complete breakdown of any solids, roots etc... and for complete mineralisation...

This can be easily acheived by rotating a single bed out of service after cropping, especially after heavy cropping of tomatoes or other extensive root system vegetables...

And if need be... the media can be screened to remove the majority of root hairs.. or even rinsed.. then left for a period... where upon a lighter cropping vegetable can be rotated...

This is certainly the approach which I employ and recommend to my clients...

Comment by RupertofOZ on December 23, 2011 at 12:00pm

Bill... regarding "reliable and reasonably cheap sequencing valve and controller to sequentially fill multiple media beds?"... indeed the "aquaponics valve" was developed for precisely this purpose...

 

But the "aquaponics valve" is sequenced by ceasation, and resumption of flow... not by an additional controller...

Comment by RupertofOZ on December 23, 2011 at 11:58am

Gina, I'm sorry.. but menadione sodium bisulfate complex is NOT a synthetic version of Potassium...

It is actually Vitamin K3... Potassium is shown as "K" as a periodic element... which might be where the confusion came from...

 

 There are two natural forms of Vitamin K, phytonadione (vitamin K1) and menaquinone (vitamin K2).

Phytonadione occurs in plants and Menaquinone is produced by bacteria in the intestine.

Menadione (vitamin K3) is a synthetic form which does not have aliphatic side chain. Menadione is a vitamin precursor of V-K2 which can be converted in the liver to active menaquinones by chemical alkylation in vivo.

Menadione Is used as a source of vitamin K in the treatment of hypoprothrombinemia against vitamin K deficiency. It is not used directly as a nutritional supplement due to high toxicity and low stability.

Menadione sodium bisulfite (MSB) is a water-soluble derivative of menadione for feed. But MSB has limited stability to light, heat, humidity, ambient pH values above neutrality and in the presence of some salts.

 

Again, with the regular water top ups required due to transpiration losses... and the insignificant amounts contained in feeds... and it's inherent instability, and solubility... I do not believe that it represents a problem...

Comment by RupertofOZ on December 23, 2011 at 11:49am

Ryan, when you said "salts" buildup, I presumed you meant "salts" in a chemical sense... as in anions, negatively charged atoms... like chlorides, nitrates, sulphates etc...

The discussion now seems to have settle on "salts" meaning Sodium Chloride.. or particularly Sodium buildup...

In all the 6-7 years I've been running my systems I, and to my knowledge, all of the other long term aquaponicists in Australia... have never seen, or encountered any thing that even vaguely suggests any Sodium buildup...

Nor are low levels of Sodium problematic per se... indeed I, and others have at times not only run systems periodically with salt levels from 1ppt - 6ppt, the latter for disease treatment.... and indeed I actually ran one of my systems at a constant level of 1ppt for nearly two years...

Likewise, both in my previous hydroponic operations, and my hybrid media bed, nft system which ran until recently for over 4 years... I would periodically add a proportion of pure sea water to my top ups... sea water being the highest concentration of naturally chelated trace elements available...

My plants thrived... as did the agricultural growth of farms in Aceh in the year after the tsunami inundated vast areas of cropping land...

I'm sorry, but unless you can provide imperical evidence to the contrary.. I'm going to have to say "myth busted"...

 

In terms of solids buildup, and development of anaerobic zones in media grow beds... again both my own experience, and that of many senior aquaponicists in Australia.. has clearly demonstrated, that correctly designed and sized grow bed... to stocking and feed levels... with the introduction of compost worms...

Has consistantly shown that no such problems occur... and I, Murray Hullam, and others have deliberately taken down grow beds that have been in operation for 3+ years, and photographed the results to demonstrate that it simply isn't the case....

 

With the grow beds acting as both solids capture, mineraliasation, and nitrification... it is paramount to size them to maximum stock and feed levels... and to provide appropriate oxygenation levels, not just for the fish... but for the nitrification process, and breakdown of solids wastes....and that is where 99.9% of people who encounter problems come unstuck...

 

If you have had clients thaqt have elevated salinity levels... then IMO... the salinity must have been introduced by other means than any content from feed... and given the uptake of salt within some plants, and declining salinity concentrations over time with the regular system top ups that are necessary with media bed systems due to transpiration loss.. I can only assume that their systems were either introducing salinity through source water, had salt added at some stages... or were really poorly designed...

 

On the question of sizing, or skimping regarding the sizing of grow beds... it in the end comes down to stocking densities and feed levels... and even allowing for the disproportionate stocking levels that Tilapia allow in comparison to most other fish... there is a grossly over-inflated level of stocking in most system...in relation to that which is actually required to provide for the nutrient needs of the plants...

This was one of the foundations of the "Friendlies" model of DWC in comparison to the UVI model...

Comment by Ryan Chatterson on December 23, 2011 at 9:18am
I havent in my personal system Chris but I don't operate under the "remove no waste" methodology. I have however dealt with 5-7 customers over the past few years that don't remove any waste and they ran into this exact problem. Through some thurough trouble shooting we were able to determine that the problems were developing from salt toxicity. We then measured the salinity of the water to confirm suspicions and after lowering the salinity, the growth rates went back to normal. So yes, I have seen it and that the only reason I even mention it.

"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."
Im all about advancing technology in this industry but the idea of using media beds isnt new techynology. I think the choice should come down to ease of use and price to build. I have no problem walking around a raft to harvest VS walking around a media bed to harvest. If you want some of the raft system to be mobile for harvesting then you just isolate those troughs and leave them dedicated to growing whatever mobile crop you want.

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