IMPROVING YIELDS WITH DECOUPLED AQUAPONICS

RAS biofilter effluent is an ideal supplement for hydroponically grown crops, with prior studies observing a significant (30-40%) improvement (1) in both the growth rate and total yield of lettuce when effluent was used to supplement a standard hydroponic nutrient solution (HNS). Traditionally, solid (insoluble) RAS waste recovery has not been a priority due to the relatively small quantity of solid waste produced and the limited perceived cost-benefit of additional infrastructure for solid waste recovery. Recent advancements in waste digestion may permit novel opportunities when applied to solid aquaculture waste reutilisation.

Although nutrient supplementation with RAS waste products (soluble and insoluble, Figure 1) improves hydroponic growth rates, prior experiments have shown nutrients such as N and P are not the primary drivers for improved growth rates of plants in the hydroponics compartment (increased growth rates were observed despite nutrient concentrations remaining constant between treatments).  Contrary to previous claims (2), our research into the effects of RAS supplementation to standard HNS grown crops indicates that it is not the living microbial community per say that has the greatest effect on crop productivity, but rather stimulatory compounds produced by that community. To investigate how waste treatment systems can augment nutrient uptake and improve crop stability, we supplemented HNS with soluble waste from the biofilter. The effect of filter sterilisation (preservation of only bacterially-produced compounds without microbial proliferation), as well as community development (consolidation around a stable rhizosphere consortium) was explored. Similar experiments were carried out using digested insoluble waste.

Consistent with prior published research, soluble RAS waste supplementation to HNS resulted in increased growth rates and total leaf mass. Insoluble waste digestion showed promising results in model systems. Preliminary results indicate that a combination of soluble and insoluble waste digestion strategies can be effective at significantly improving hydroponic crop productivity compared to nutrient solutions alone. Future work will use cost-benefit models to determine the economic suitability for aquaponic operations.

References: 1.      Delaide B, et al. Water. 2016.

2.Wielgosz Z, et al. Horticulturae. 2017.