Abstract
Aquaculture is an important source of animal protein and a key contributor to global food security. However, aquaculture can exert a negative effect on the aquatic environment due to the release of effluents containing high nutrient levels. In integrated multi-trophic aquaculture (IMTA), the waste produced by one species is the input for another, referred to as extractive species (ES). Potential ES include plants. In the present study, it was explored whether Lemna minor can be used to remove nitrogen and phosphorus from aquaculture wastewater. A representative synthetic wastewater was designed based on the composition of aquaculture effluents found in the literature. Synthetic wastewater was found to be a suitable medium for growth of Lemna minor, and plants readily took up NH4+-N, NO3-N and PO43--P. In particular, NH4+-N concentrations rapidly decreased. The highest removal rates per square meter of water surface, calculated for NH4+-N, NO3-N and PO43--P, were, respectively, 158, 206 and 32 mg·m-2·day-1, and these rates were achieved at a plant surface density of 80%. As removal of nutrients is essentially a surface area–related process, the effect of plant density on nutrient uptake was determined. Uptake of nutrients per square meter of surface area was highest at the highest plant density. Yet, when uptake rates were calculated per square meter of water area covered by Lemna fronds, the highest removal rates were found at the lowest plant density, and this is likely to be associated with a reduced intraspecific competition. The present work enables the calculation of potential nutrient uptake by Lemna minor and lays the foundation for a more scientific approach to the design of duckweed-based aquaculture wastewater treatment systems.
Highlights
Global food security refers to a scenario in which everybody has access to sufficient, safe and nutritious food (FAO 2001)
Food quality is a major consideration in the concept of food security and, especially, the supply of quality protein is of concern (Tuomisto 2010)
The literature was mined for data on the composition of freshwater aquaculture effluents and concentrations of NO3 -N, NH4+-N and PO43--P
Summary
Global food security refers to a scenario in which everybody has access to sufficient, safe and nutritious food (FAO 2001). Food quality is a major consideration in the concept of food security and, especially, the supply of quality protein is of concern (Tuomisto 2010). This, in turn, has led to increased emphasis on fish farming to improve food security (Ahmed and Lorica 2002; Allison 2011; Jennings et al 2016). The global production of farmed fish increased from 105.46 million tonnes in 2016 to 110.21 million tonnes in 2018 (Tacon 2018). The total global production is valued 243.26 billion of US dollars (FAO 2018). The growth of the aquaculture sector is set to continue, with the European Union having invested €3.4 billion in the aquaculture sector over the period 2000–2020 (Guillen et al 2019)
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