A Kinetic Approach for Employing Two Duckweed Species, Lemna minor, and Spirodela polyrhiza, in the Sustainable Aquaculture Wastewater Treatment and Fish Feed Production

Abstract

Duckweed, a widely used natural fish feed, has also become more popular as the phytoremediation agent for wastewater, including one sourced from aquaculture. These two features indicate that duckweed can be utilized in a sustainable aquaculture system by treating and reclaiming nutrients from wastewater and then harvesting them for fish feed production. Hence, this study attempted to assess the approach of the two most known duckweed species, i.e., Lemna minor and Spirodela polyrhiza, in depleting NH₄ and PO₄ from synthetic controlled aquaculture wastewater as well as to understand their yield based on the N : P ratio. Cultivation in synthetic aquaculture wastewater media was carried out, followed by nutrient uptake and growth analysis. According to statistical analysis, both L. minor and S. polyrhiza could remove NH₄ and PO₄ with a relatively equal rate (p-val > 0.050). Nonetheless, both duckweed species absorb nitrogen more easily than phosphorous (p-val < 0.050). Considering the yield based on nutrient uptake, NH₄ drove a more efficient yield for L. minor to S. polyrhiza at 16.70 g dry biomass/g NH₄ and 14.14 g dry biomass/g NH₄, respectively. Meanwhile, a higher yield was observed on S. polyrhiza than on L. minor regarding PO₄ concentration, at 19.31 g dry biomass/g PO₄ and 9.10 g dry biomass/g PO₄, respectively. Therefore, a strategy to remove nutrients and produce biomass for fish feed can be formulated based on the N : P concentration ratio, where L. minor tends to produce biomass more rapidly in a higher N : P ratio, whereas S. polyrhiza works in the opposite.