Abstract
•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.