Nutrients recovery from aquaculture waste for use as fertilizer in soilless growth systems

M. Ezziddine, H. Liltved
In coming decades agriculture must produce more food with less space and resources. To overcome these challenges, new farming approaches are needed. Investments in smart soilless production systems may contribute to solve these problems. However, todays hydroponic systems rely on inorganic fertilizers which are mined from scarce and non-renewable resources. The aim of this work was to convert aquaculture waste to valuable fertilizer by aerobic digestion (AD). A mixture of drain-water from swirl separators and backwash-water from particle-filters were collected from a local land-based fish-farm with recirculation of water. Three sets of experiments were conducted in duplicate in batch aerated reactors for three weeks. For the first and second set, pH was kept at 7 and 5, respectively. For the third set, the pH was not adjusted and was in the range of 8-9. Aerobic digestion at pH 7 and 5 showed similar mobilization performance with an increase of soluble macronutrients and micronutrients to concentrations close to or exceeding mineral levels recommended for soilless growth systems. At pH 7, the concentrations of soluble phosphorus (P), nitrogen (N), potassium (K), calcium (Ca) and magnesium (Mg) increased by factors of 12.9, 4.9, 1.7, 3.2 and 2.0, respectively. At pH 5, the same concentrations increased by factors of 19.0, 5.4, 1.5, 5.1, 2.4, and 2.0, respectively. The mineral analysis suggested that the resulting nutrient-rich solution can be used for soilless agriculture. However, the ratio of NO3-N to NH4-N was low compared to recommended values. Further studies will be carried out to stimulate nitrification during AD to produce a better balanced nutrient solution and to evaluate the performance of the recovered nutrient solution on plant growth.
Ezziddine, M. and Liltved, H. (2021). Nutrients recovery from aquaculture waste for use as fertilizer in soilless growth systems. Acta Hortic. 1305, 399-406
DOI: 10.17660/ActaHortic.2021.1305.52
aerobic digestion, aquaponics, hydroponics, mobilization, nutrient solution, nutrient recovery, organic fertilizer

Acta Horticulturae