The indigenous bacteria, cow dung and sewage sludge were used as seed microflora sources to ferment
sweet potato into hydrogen and ethanol under batch cultivation at a temperature of 37 C. Hydrogen and
ethanol production was evaluated based on their yields (HY and EY) and production rate (HPR and EPR)
at various sweet potato concentrations (30e240 g/L), sweet potato particle diameters (6.38 mm) and initial cultivation pH conditions (4.0e9.0). The experimental results indicate an interesting
finding that sweet potato fermentation without adding external seed (i.e., the fermenter contained
only the indigenous bacteria which were identified to have seven species) could produce hydrogen and
ethanol (EtOH). The indigenous bacterial community analysis showed that Klebsiella oxytoca, Clostridium
fimetarium, Grimontella senegalensis, and Enterobacter asburiae (or Escherichia coli) were present at peak
ethanol production and two more species Ruminococcus schinkii and Lactovum miscens were present at
peak hydrogen production.
The externally seeding strategy could enhance the hydrogen production from sweet potato with peak
cumulative H2 production potential (HP) of 120 mmol H2/L-reactor using sewage sludge. However, the
cow dung seed showed more ethanol production than hydrogen with peak concentration of
12,146 mg COD/L. Increasing the sweet potato concentration could enhance the HPR and HP values.
Maximum HY of 1.24 mol H2/mol hexose was obtained at a substrate concentration of 150 g/L with an
initial cultivation pH of 6.7 and particle diameter