Part three of four
In my last two columns, I discuessed what is a Recirculating Aquaculture System (RAS) and how it works by identifying the ideal parameters of the water and filtering it so that it can be reused and thus recycled.
The filtration combines mechanical (removal of solids) and biological conversion of the harmful buildup of unideal contents in the system. We then discussed hydroponics and how this technology can be looped together with RAS to form what is aquaponics — subject to some modifications, of course.
How can a hydroponics system be merged with RAS?
Remember that the nitrates, the dissolved minerals in the water, and the other minerals found in the undissolved solids (that must undergo re-mineralization), are actually good sources of nutrients for plants. Thus, the linkage of the RAS system with a hydroponics system becomes a useful interconnection that helps reduce the discharge of solid wastes which, after going through mineralization, can be used by hydroponics component. In effect, the plants prevent accumulation of minerals that become harmful to the fish by using these as nutrient sources.
A typical RAS needs to undergo partial water exchange of around five to 10 percent of the total volume of the water every 24 hours. The purpose is to prevent the system from having too much mineral presence in the water.
Attaching a hydroponics component to the RAS removes the need for daily partial water exchange because mineral (and nitrates) accumulation no longer significantly happens at a rate that is dangerous to the fish. They become plant food instead.
As an added bonus, the grow areas of the hydroponics attachment to the RAS system has a high Specific Surface Area (SSA) capable of performing biofiltration. Basically, the hydroponics component becomes the biofilter where the beneficial bacteria, necessary for the conversion of toxic ammonia into nitrites and then, finally, nitrates, lives. There’s no need for a separate biofilter anymore, provided that there is enough SSA in the grow areas. This is the benefit provided by the convergence of RAS and hydroponics in the form of Aquaponics.
Sump tank and recirculation
To summarize the linkage, for Aquaponics, the usual water flow looks like this (based on the UVI model): Fish Tank → RFS → Mechanical Filtration → Degassing Tank → Hydroponic Component (Grow Beds / Biofilter) → Sump Tank → Fish Tank. And the entire cycle is repeated over and over while fish and plants grow in the system and the water is merely recycled.
At this point, you may have noticed that there’s a new item in the list, the “sump tank.” What is it?
In essence, it is a tank located at the lowest point of the system. It’s like the central station. Water is pumped from the sump tank to the fish tank located at the highest point of the system, and water then flows to the different components of the system, thanks to gravity. Water then returns to the sump tank and the entire process is repeated again. Recirculation is achieved.
Best of all, in the case of aquaponics, along with the fish, you get herbs, leafy greens and fruiting vegetables to boot. Not a bad deal, right?