Growth and nutrient uptake rates of duckweed cultivated on anaerobically digested dairy manure

Nutrient cycling from flushed dairy manure systems to croplands is a national research priority for sustainable dairy operations, resource utilization, and environmental protection. Cultivating aquatic plants on dairy wastewaters has been considered an effective approach for wastewater treatment/reuse and nutrient recycling. This study aimed to investigate nutrient uptake and biomass production of duckweed strains on dairy wastewater. Three duckweed strains, namely Landoltia punctata 0128, Lemna gibba 7589, and Lemna minuta 9517, were cultivated on anaerobically digested (AD) dairy manure wastewater over a period of 28 days. The highest reduction rate of total nitrogen (TN) was achieved by L. punctata from the AD dairy manure with a dilution ratio of 1:18 (83.1 mg·L^-1 TN) at 11.6% (±1.64%). The highest reduction rate of total phosphorus (TP) was achieved by L. punctata from the AD dairy manure with a dilution ratio of 1:27 (6.7 mg·L^-1 TP) at 15.4% (±4.4%). The corresponding fresh weight-based growth rate constants of L. punctata were 0.11 g·d^-1 and 0.17 g·d^-1 for the dilution ratios of 1:18 and 1:27, respectively. It has been shown that, among the three duckweed strains tested in this study, L. punctata has the greatest potential to be cultivated on the medium of diluted AD dairy manure for best N and P reduction and biomass production.