A Comparison of Three Different Hydroponic Sub-systems (gravel bed, floating and nutrient film technique) in an Aquaponic Test System

Abstract

Murray Cod, Maccullochella peelii peelii (Mitchell), and Green Oak lettuce, Lactuca sativa, were used to test for differences between three hydroponic subsystems, Gravel Bed, Floating Raft and Nutrient Film Technique (NFT), in a freshwater Aquaponic test system, where plant nutrients were supplied from fish wastes while plants stripped nutrients from the waste water before it was returned to the fish. The Murray Cod had FCR's and biomass gains that were statistically identical in all systems. Lettuce yields were good, and in terms of biomass gain and yield, followed the relationship Gravel bed > Floating > NFT, with significant differences seen between all treatments. The NFT treatment was significantly less efficient than the other two treatments in terms of nitrate removal (20% less efficient), whilst no significant difference was seen between any test treatments in terms of phosphate removal. In terms of dissolved oxygen, water replacement and conductivity, no significant differences were observed between any test treatments. Overall, results suggest that NFT hydroponic sub-systems are less efficient at both removing nutrients from fish culture water and producing plant biomass or yield than Gravel bed or Floating hydroponic sub-systems in an Aquaponic context. Aquaponic system designers need to take these differences into account when designing hydroponic components within aquaponic systems.

Hydroponic systems and water management in aquaponics: a review

“…They concluded that the floating system is cheaper in construction and maintenance, whereas the mediumbased system provides plants with added stability and can thus support larger plants. Lennard and Leonard (2006) found the NFT system to be less efficient in terms of nutrient removal and lettuce yield than the medium-based or floating raft system Schmautz et al (2016) obtained significantly lower tomato production in NFT than floating raft system but not than medium-based system. The lower nutrient removal capacity may be due to the restricted contact between the roots and the water.…”

“…The choice of hydroponic type for an AP system may be based on the independent advantages conferred by any particular hydroponic component (Lennard and Leonard, 2006) or on life cycle assessment impact (Forchino et al, 2017). All the methods represented in Figure 1 can be integrated in an aquaponic system (Pattillo, 2017).…”

“…Lennard and Leonard (2006) evaluated the effect of hydroponic system type (gravel bed, floating or NFT) on nutrient stripping, plant yields and fish growth in a 21-day experiment with Murray cod (Maccullochella peelii peelii) and lettuce (Lactuca sativa). They found the highest production in the gravel bed (5.05 kg m -2 ), followed by floating rafts (4.47 kg m -2 ) and NFT (4.13 kg m -2 ) and no effect of hydroponic system on fish growth.…”

“…Plants grown in medium-based and floating hydroponic systems have their entire roots in contact with the water, providing them with more surface area to assimilate nitrate. In contrast, plant phosphate assimilation is not simply dependent upon the root area available to the water column (Lennard and Leonard, 2006) but also by water temperature (Adams, 1993) and pH (Raviv and Leith, 2008).…”

“…Nevertheless, NFT appears be an appropriate technology for aquaponics, based on capital cost and ease of use (Lennard and Leonard, 2006;Goda et al, 2015). Probably due to these reasons, some AP companies (i.e., UrbanFarmers, www.urbanfarmers.com) are using NFT channels for hydroponic section in commercial scale AP.…”