Significant factors affecting the economic sustainability of closed aquaponic systems. Part III: plant units

Autor: Palm, Harry W.; Nievel, M.; Knaus, U.
In:

AACL BIOFLUX

Bandangabe: 8
Auflage: 1
ISBN: 1844-9166
Seite: 89 - 106
Jahr: 2015

Einordung:
Institut: Professur Aquakultur und Sea-Ranching

Abstract:
Abstract. The hydroponic unit of two identical closed ebb-flow substrate aquaponic systems for warmwater
fish were tested for water parameter differences of dissolved oxygen (DO) [mg L-1], temperature
[°C], pH and phosphorus [mg L-1] under Nile tilapia (Oreochromis niloticus) cultivation. Each system
contained 3.7 m3 water, and the relationship of the water volume in the aquaculture tank to the settling
basin (sedimenter, clarifier), the biofilter and the hydroponic units was 2.25:1:0.075:0.6 (fish
tank:hydroponic unit = 3.75). The hydroponics were built as gravel bed aggregate systems with a single
nutrient enriched water inlet for each of four plant units, and a horizontal sub-irrigation towards the
outlet. Related to an increasing feed input into the fish tanks, DO levels in the hydroponic units were
lowest inside the system (1-4.7 mg L-1). This is a favourable place for oxygen level monitoring to indicate
a stable performance. Declining DO trends were observed in both cycles, with significant differences (p <
0.05) within cycle I and II on 4 consecutive days. Oxygen means of cycle I and II were significant only
on day I. Inside the 2 m2 plant boxes, slightly decreasing trends in DO distribution towards the outlet
were observed. Time series of all four experimental days (ANOVA, p < 0.05) showed varying values of
phosphorus with highest levels on sampling day III in both cycles. Following an increase in feed input, a
sluggish phosphorus accumulation inside the plant boxes was observed. Parallel arrangement of the 4
plant boxes in each cycle had no influence onto water parameters within each plant box. Within each
cycle no trend was observed, total parameter values differed only slightly, influenced by the system
design of the hydroponic units. Plant growth was different in cycle I and II. Best growth was recorded
close to the nutrient enriched water inlet into the plant boxes, assessing the chosen central nutrient
water irrigation system as sub-optimal for plant growth. Cucumber and zucchini showed better biomass
gain (sum 7.60 kg) in plant box II of cycle II than in other plant boxes, suggesting variable conditions
inside the plant boxes of the tested aquaponic system.
Key Words: aquaponics, hydroponics, sub-irrigation, system design, ebb and flow system, fish and plant
combination, Tilapia.

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