Doctor

Aquacult Int (2006) 14:539–550 DOI 10.1007/s10499-006-9053-2 ORIGINAL PAPER

A comparison of three different hydroponic sub-systems (gravel bed, floating and nutrient film technique) in an Aquaponic test system
Wilson A. Lennard Æ Brian V. Leonard

Received: 18 August 2004 / Accepted: 7 April 2006 / Published online: 27 May 2006 Ó Springer Science+Business Media B.V. 2006

Abstract MurrayCod, 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. TheMurray 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), whilstno 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 thanGravel 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. Keywords Aquaponic Æ Hydroponic Æ NFT Æ Biological nutrient removal Æ Wastewater Æ Murray Cod Æ Nitrate Æ Phosphate Introduction Aquaponics is the integration of hydroponic plant production intorecirculating fish aquaculture systems (RAS). The hydroponics control the accumulation of waste
W. A. Lennard (&) Æ B. V. Leonard School of Applied Sciences, Department of Biotechnology and Environmental Biology, RMIT University, Building 223, Level 1, Plenty Road, 71, Bundoora, Vic. 3083, Australia e-mail: S8702774@student.rmit.edu.au

123

540

Aquacult Int (2006) 14:539–550

nutrients fromfish culture (Rakocy and Hargreaves 1993), which may lower overall consumption of water (McMurtry et al. 1997) and produce additional, saleable crops (Rakocy and Hargreaves 1993). Early researchers showed that waste nutrients could be ‘‘stripped’’ from fish culture waters using hydroponically grown plants (Naegel 1977; Lewis et al. 1978; Waten and Busch 1984), with the hydroponic component generallyusing a sand/gravel/aggregate culture bed (Lewis et al. 1978; Waten and Busch 1984; McMurtry et al. 1993). Both floating (or ‘‘raft’’) and Nutrient Film Technique (NFT) hydroponic plant growth components have also been independently tested within the context of an Aquaponic system (Rakocy and Hargreaves 1993; Rakocy et al. 1997; Seawright et al. 1998; Adler et al. 2000a), but little literature isavailable that compares all three hydroponic growth systems against each other in an Aquaponic context. The choice of hydroponic growing system within an Aqauponics context may be based on the independent advantages conferred by that particular hydroponic component. For example, sand/gravel systems may remove the requirement for a separate biofilter, as the substrate will also act as a substrate fornitrifying bacteria, and therefore replaces conventional biofilters (McMurtry et al. 1997; Seawright et al. 1998; Dontje and Clanton 1999). Similarly, the gravel/sand substrate may also act as a solids filtering medium (McMurtry et al. 1997; Seawright et al. 1998). On the other hand, proponents of floating or raft hydroponic components argue that sand or gravel substrates are excessively heavy...