Hydroponic horticulture using residual waters fromOreochromis niloticusaquaculture with biofloc technology in photoautotrophic conditions withChlorellamicroalgae

Abstract

Protein‐dependent aquaculture generates large amounts of nutrient‐rich residuals; a feasible way to develop sustainable production systems is to integrate Decoupled Aquaponic Systems (DAPS) with residual water bioprocesses, to combine Photoautotrophic Biofloc Technology (P‐BFT) aquaculture and hydroponic horticulture. This study describes the characteristics of residual water from Oreochromis niloticus aquaculture performed with P‐BFT inoculated with Chlorella microalgae, reared during the nursery (180 fish m3) and grow‐out (55 fish m3) phases. The experiment included five treatments: photoautotrophic BFT inoculated with Chlorella sp. (M), C. sorokiniana 2714 (CV), and C. sorokiniana 2805 (CS), and chemoautotrophic (Q) and heterotrophic (H) as controls. Elemental characteristics in liquid and solid residual fractions (15 macro‐ and micronutrients) were compared among treatments and against Hoagland & Arnon solution with hydroponics and used in Nutrient Film Technique (NFT) hydroponic horticulture including five plant species: lettuce (Lactuca sativa), pak‐choi (Brassica rapa subsp. chinensis), rocket (Eruca sativa), spinach (Spinacia oleracea) and basil (Ocimum basilicum). The physicochemical parameters were ideal for O. niloticus and plants. The relationship between N:P was ideal until weeks 16–22 in the photoautotrophic treatments, compared with hydroponic solutions. Micronutrient content was greater in the solid than a liquid fraction. The best BFT effluent regarding fish and plant growth was photoautotrophic treatments. Oreochromis niloticus BFT aquaculture in photoautotrophic mode using microalgae Chlorella inoculations provided residual water beneficial to hydroponic horticulture in DAPS located in coastal arid zones where freshwater is scarce, improving aquaculture performance and reusing water and nutrients.

FLOCponics: The integration of biofloc technology with plant production

“…Additionally, recent studies have evaluated the macro-and micro-nutrients available in the water and the solid portion (visible biomass) of FLOCponics systems, in an attempt to minimize uncertainty in predictions. 48,123,124,134 In general, lower concentrations of nutrients in FLOCponics water as compared to hydroponic solutions have been found. 123 On the other hand, when compared to traditional aquaponics using RAS, higher concentrations of P, K, Ca, S and Fe were found and seem to be associated with the practice of external carbon addition.…”

“…The influence of nutrient uptake by BFT microorganisms on the availability of nutrients for plant production is yet unclear. At this moment, the results have indicated that running a mixotrophic or chemoautotrophic BFT would be the best option for FLOCponics systems 134,140 due to the expected predominance of nitrifying communities (higher concentration of nitrate in water) instead of a heterotrophic‐based medium. Another approach related to BFT microorganisms that must be clarified is whether a thin flocs biofilm on plant roots has the potential to boost or harm the nutrient uptake by the plants.…”

“…On the other hand, when compared to traditional aquaponics using RAS, higher concentrations of P, K, Ca, S and Fe were found and seem to be associated with the practice of external carbon addition 48,124 121,122,134 . Fimbres‐Acedo et al 134 suggested that these solids could be mineralized, enhancing nutrient availability.…”

“…Unlike in biofloc-based systems without integration, the use of filters in FLOCponics was intended to try to avoid the flow of particulate matter to the hydroponics subsystems as such particulates may impair plant growth. Except for the systems run by Fimbres-Acedo et al, 133,134 Doncato and Costa, 124 all the others constantly recirculated the water through the filters and 46% of them used some mechanisms to return the decanted biofloc/sludge to the BFT subsystem. Fimbres-Acedo et al 133,134 employed a decoupled system where the hydroponics subsystems received water from the BFT subsystem only in the beginning and middle of the experiment.…”

“…Except for the systems run by Fimbres-Acedo et al, 133,134 Doncato and Costa, 124 all the others constantly recirculated the water through the filters and 46% of them used some mechanisms to return the decanted biofloc/sludge to the BFT subsystem. Fimbres-Acedo et al 133,134 employed a decoupled system where the hydroponics subsystems received water from the BFT subsystem only in the beginning and middle of the experiment. At these moments, the water from the BFT subsystem was pumped to the 300 L settling tank and left to settle for 24 h. Subsequently, the supernatant was transferred to a 1000 L aerobic mineralization bioreactor (AEMBR), filtered with a 5 µm bag filter and then directed to the hydroponics subsystem.…”