Duckweed harvested from a swine wastewater treatment system was evaluated for its potential as a fermentation feedstock for the production of biohydrogen. The effects of pretreatment and fermentation conditions on biohydrogen production were investigated in laboratory-scale batch experiments. The results showed that mild acidic thermal pretreatment (1% H2SO4 and 85 degrees C for 1 h) was more effective in improving the fermentability of duckweed than either thermal or mild alkaline thermal pretreatments. Fermentation of acid-pretreated duckweed resulted in a biohydrogen production of up to 75 mL H-2 per g dry duckweed in 7 days (at a H2 concentration of 42%), which is comparable with other plant biomass. Overall, the results show that small aquatic plants such as duckweed can be promising substrate for biohydrogen production. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.