Nutrient flow is the biggest challenge when considering aquaponics in general. This problem becomes much larger when we start attempting to use aquaponics in an open system. In a closed loop aquaponic system, you can heavily influence the nutrient flow to the plants by selectively stocking and feeding fish to suit ones needs.
In an open system, this tool is not entirely removed though. It is more inverted. We would approach this by tailoring the crops to the level of pollution of the nutrient levels in a given region.
We would also have several advantages over most aquaponic systems.
First and foremost is that our grown product is actually a byproduct of our goal of removing the excess nutrient from the water system.
The next advantage is that the primary waste products creating this pollution are farm and lawn run off, both of which are mostly the nutrients needed to grow most marketable plants.
Even with those considerations, some management will be needed to ensure satisfactory levels of nutrient are supplied, so that the clean up byproduct crops can provide a profitable harvest to fund the system once it is up and running.
This can be accomplished by utilizing primed water storage, and by utilizing evaporation in the first stage of water purification.
What I mean by primed water storage is using large cisterns to gather water when the pollution levels are at their peak levels. This is likely the first heavy rains after crop fertilization, which also happens around the same schedule as lawn fertilizing. By filling tanks at this time, we will start with a base of nutrient heavy water. The fresh water that is pumped into it during less polluted times will slowly dilute, but this should keep levels in the system higher than the river levels throughout the year when pollution levels are lower.
Using evaporation in the first stage (I will describe this in detail in a later system article) will concentrate the remaining nutrient, and the evaporated water will be routed back to the outflow tank to be returned to the river.
Another major consideration of nutrient flow in this system is toxins and chemicals we don’t want. The sad fat is that we need the plants to uptake these chemicals as well. Which is the primary consideration for not utilizing this system to produce food. Nothing grown in this system should ever be considered for human consumption. I would further propose that all plant waste be routed into a hydrothermal carbonization process so that we can isolate the more problematic compounds. Again, we will explore that in a later article, including a subsystem design that will be primarily for fuel production with this system partnered with hydrothermal carbonization.
The long an the short of this piece is that IF we run into major issues supplying enough nutrient for the system, then we have accomplished our goal of removing pollution from the rivers and will have a new, much higher quality problem.
For more information on how to fix Dead Zones in the Gulf of Mexico and the mouth of other rivers, follow this link –>
