The Potential of Anaerobic Remineralization in Aquaponic Systems

As you guys might have noticed, we are currently running an experiment on the anaerobic remineralization potential of RAS-derived fish sludge. In order to clarify open questions regarding the impact of anaerobic effluents on plant growth, we have conducted a small experiment. In that experiment we compared the lettuce growth (as well as shoot:root ratios) for lettuces grown in RAS water that has been supplemented with either anaerobic or aerobic fish sludge supernatant.  The experimental setup can be seen in Figure 1.

Figure 1. Schematic outline of each experimental setup.

What we observed is that the lettuce plants grown in the hydroponic system supplied with supernatant from an anaerobic reactor (i.e. anaerobic remineralization) had significantly better performance with respect to weight gain than both, those in the system where supernatant from the aerobic reactor was added, as well as the control system (Figure 2). The opposite effect was observed with regard to the root growth of the plants (Figure 3), leading to a higher shoot-to-root ratio of the system treated with anaerobic effluents compared with the other two groups.

Figure 2. Lettuce shoot fresh weight in the aerobic (AER), anaerobic (ANA), and RAS systems after 35 days.

Figure 3. Lettuce root fresh weight in the aerobic (AER), anaerobic (ANA), and RAS systems after 35 days.

We hypothesize that this effect was caused by the presence of NH₄⁺ as well as dissolved organic matter, plant growth promoting rhizobacteria (PGPR) and fungi, and humic acid, which are predominantly present in anaerobic effluents. This is the reason why we are currently focusing on anaerobic remineralization follow-up experiments. Those who are interested in a more detailed analysis, feel free to read our whole publication on “The Effect of Anaerobic and Aerobic Fish Sludge Supernatant on Hydroponic Lettuce“.