Growing aquatic plants in nutrient-rich wastewaters for
phytoremediation is a promising process because of its potential
for bioresource/bioenergy recovery from waste
streams at low overall cost. Duckweed (Lemnaceae) is a small
free-floating aquatic plant that proliferates through vegetative
budding of new fronds and can double its mass within 16e24 h
under ideal conditions [1,2]. Duckweed has four genera:
Lemna, Spirodela, Wolffia, and Wolffiella. A large diversity and
wide geographic distribution have been observed among the
many duckweed species [1,3]. Because of their fast growth,
great tolerance to high nutrient levels, and extraordinary
nutrient uptake ability, duckweeds of various species have
been intensively studied for the treatment of nutrient-rich
wastewaters, especially swine wastewater [4e7]. Cheng et al.
grew Lemna minor 8627 on synthetic swine wastewater in a
laboratory environment and reported nitrogen and phosphorus
removal rates of 3.36 g N m2 day1 and
0.20 g P m2 day1, respectively, with the highest duckweed
growth rate reaching 29 g m2 day1 (dry weight basis) [8]. Xu
et al. operated a pilot-scale semi-continuous duckweed-based
swine wastewater treatment system for 16 weeks and reported
that duckweed Spirodela polyrrhiza could grow very
rapidly on the diluted effluent of anaerobically digested swine
manure. With frequent duckweed harvesting, an average
ammonia removal rate of 1.12 g N m2 day1 and a duckweed
biomass growth rate of 10.7 g m2 day1 (dry basis) were
reached