wastewater normally has a relatively low carbohydrate content
but a high protein content. Assuming the hexose content
of lignocellulosic biomass comprises roughly 30e50% of the
dry biomass weight, the hydrogen yields in the previously
reported studies were multiplied by 0.3 or 0.5 to convert them
to mL H2 g1 dry biomass for comparison. After unit conversion,
the hydrogen production from corn stover, wheat straw,
sugarcane bagasse, rice straw, and sweet sorghum ranged
from about 30 to 180 mL H2 g1 dry biomass. The comparison
shows that, although duckweed plant was believed to have a
cell wall structure more amenable to chemical and biological
attack, the hydrogen production from duckweed was comparable
to, or slightly lower than, most lignocellulosic feedstocks.
This is probably because of the composition of
duckweed biomass. Duckweed has a high content of protein,
which is not as effective as carbohydrate in fermentative
hydrogen production, because a significant amount of
hydrogen is consumed in organic nitrogen-to-ammonia conversion
during feedstock [50]. To improve the hydrogen potential
of duckweed, post-harvest procedures can be adopted
to increase the carbohydrate content of duckweed plants. Xu
et al. reported that after cultivating duckweed in a nutrientdeprived
environment for a week, the starch content of
duckweed was increased from 18% to 30% while the net
biomass was doubled [14]. It is reasonable to expect that the
hydrogen yield can be similarly increased if a similar enrichment
step is included prior to using duckweed for hydrogen
production.