Duckweed systems for eutrophic water purification through converting wastewater nutrients to high-starch biomass: comparative evaluation of three different genera (<i>Spirodela polyrhiza</i>, <i>Lemna minor</i> and <i>Landoltia punctata</i>) in monoculture or polyculture

Abstract

The polyculture of different duckweed species is likely to integrate their advantages in removing pollutants and starch accumulation. Here, pilot-scale comparisons of three duckweed species (<i>Spirodela polyrhiza</i> K1, <i>Lemna minor</i> K2 and <i>Landoltia punctata</i> K3) in monoculture and polyculture were investigated. Results showed that the TN (total nitrogen) and TP (total phosphorus) in wastewater decreased from 6.0 and 0.56 mg L^-1 to below 0.5 and 0.1 mg L^-1, respectively. Namely, the water quality improved to Grade II under the Chinese standard. The highest TN and TP removal efficiencies were found to be 99.1% and 90.8% in the polyculture. Besides, the starch content of <i>S. polyrhiza</i> K1, <i>L. minor</i> K2, <i>L. punctata</i> K3 and the polyculture reached 24.8%, 32.3%, 39.3% and 36.3%, respectively. Accordingly, their average starch accumulation rates were 1.65, 2.15, 3.11 and 2.72 g m^-2 d^-1, respectively. Our results suggested that <i>L. punctata</i> K3 was a promising energy feedstock due to it having the highest starch production. The advantages of different duckweed species were investigated. In the polyculture, the pollutants were efficiently removed from wastewater, with a high starch accumulation. This study supplies a new insight into the application of duckweed in eutrophic water advanced treatment coupled with starch production.