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Organic Solids – 12 Nuggets You Need to know

With all this talk of removing organic solids from aquaponic systems, many people are now putting some form of solids filtration in their systems at home and find they perform much better than those without.  This is a positive step forward.  But how do we use these solids and what does it all mean? This statement is often raised in discussion, “why would you take all that nutrient out” in defense of not removing solids.  It is a really good question and the answer is very simple, many that are removing solids are, for want of a better term “mineralizing” them and introducing the rich dissolved plant available nutrients back into the system down stream from the fish. As we progress forward in the Evolution of Aquaponics, we will see many more people adding this simple process to increase the productivity of their systems and completely use all the organic solids generated by the fish in a manner which can be controlled.  Permit me to explain a little more. [heading] A little understanding about organic solids [/heading] The basics for mineralizing the organic solids from uneaten fish feed and poop is it takes lots of oxygen and some may need some carbon thrown in.  We will talk about the carbon later.  For now, let’s stay focused on the oxygen. What is interesting about Chemistry is (don’t nod off), the names of the compounds tell us quite a bit about what it is made up of.  You will notice that plants like Nitrate as a primary Nitrogen source.  So what’s in it?  The “Ate” at the end tells us it has oxygen (NO3) and plants like most (not all) of the compounds that end with “Ate” so you can associate it with food (eat, ate.. lol.). Anyways, polyatomic ions (word of the day), require oxygen to make them.  Most fish feed will contain a small amount of phosphorus (about 0.9%) as a combination of organic phosphorus and inorganic phosphate. A majority is not plant available (bone meal etc) and we rely on bacteria to do some converting just like we rely on bacteria to convert our nitrogen sources to plant available inorganic compounds like Nitrate.  Our little saprotrophs or heterotrophs help with this process help with converting other organics into inorganic plant food. Mineralization of organic solids is a similar biological process to nitrification but different as the primary species we are looking to culture play be a different set of rules to our chemoautotrophs.  Just like our nitrifiers, oxygen is the key to mineralizing solids efficiently.  They can be broken down without oxygen but the result may not be what you are looking for and can create toxic compounds like methane and hydrogen sulfide.  These two compounds will be associated with poor solids removal systems and anaerobic processes and they don’t belong in our growing systems. One significant difference between nitrifiers and these bacteria and fungi is they don’t require media, they basically live on the organic particle and eat it until gone then fall onto the next one.  Like oneof those guests that never leave your house “couch jumper” but these guys will eat the couch!. So no biomedia required! What do we know?   Majority of nutrients in your system in the form of organic solids are not plant available These organic solids will contain 90% of the phosphorous input which is key to plant yield Solids will also contain most of your micro nutrients from your fish feed Different groups of bacteria oxidize, metabolize, catabolize or bio-digest the organic solids Some of these microflora are antagonistic to pythium so great to have You can introduce (inoculate) cultures of bio remediation just like nitrifiers This mineralization process is very slow in media grow beds and is often ineffective To speed up the process you will need lots of oxygen (primary limiting factor) Your bio-digester does not need bio-media These bacterial group will drastically lower your pH Some systems may require an additional organic carbon source to work well Mineralization is best practiced separately to your aquaponic system   These bacterial colonies and how they work are very complex but you really only need the basics to make full use of all the solids in your aquaponics efficiently and with some level of control. This is something we touched on in one of my workshops and I have had quite a few questions wanting clarification (what is that other blue drum for?).  So in the following post I will take processing organic solids and the evolution of aquaponics one step further and show you how to do this on a shoestring budget. Regards Paul…

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