Effect of zinc ions on nutrient removal and growth of Lemna aequinoctialis from anaerobically digested swine wastewater

•Lemna aequinoctialis (LA) could grow well in anaerobically digested swine wastewater (ADSW).•There exited an optimal Zn2+ concentration for nutrient removal and growth of LA in ADSW.•The peak content of photosynthetic pigments in LA occurred earlier for a higher concentration of Zn2+.•High contents of high value-added vitamin E in LA could be produced at high concentrations of Zn2+ in ADSW. The effect of Zn2+ on ammonium and phosphorous removal and duckweed growth was evaluated for treatment of anaerobically digested swine wastewater (ADSW) at various initial Zn2+ concentrations ranging from 1.0 to 15mg/L. Lemna aequinoctialis taken from a local pond was selected for the treatment, and its fresh weight and contents of proteins, photosynthetic pigments, and vitamin E were examined. Results showed that the optimal Zn2+ concentration was 5.0mg/L for NH3-N and TP removal, the duckweed growth, and the accumulation of proteins in the duckweed. A maximum content of photosynthetic pigments increased with the increase of initial Zn2+ concentration, and it arrived earlier for a higher concentration of Zn2+. Vitamin E content in the duckweed reached 4.5mg/kg at 15mg/L Zn2+ in 12-day cultivation, which showed the potential for producing and harvesting a high value-added product of vitamin E by culturing duckweed in ADSW.