The indigenous bacteria, cow dung and sewage sludge were used as seed microflora sources to fermentsweet potato into hydrogen and ethanol under batch cultivation at a temperature of 37 C. Hydrogen andethanol 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 (<1.19 mm to>6.38 mm) and initial cultivation pH conditions (4.0e9.0). The experimental results indicate an interestingfinding that sweet potato fermentation without adding external seed (i.e., the fermenter containedonly the indigenous bacteria which were identified to have seven species) could produce hydrogen andethanol (EtOH). The indigenous bacterial community analysis showed that Klebsiella oxytoca, Clostridiumfimetarium, Grimontella senegalensis, and Enterobacter asburiae (or Escherichia coli) were present at peakethanol production and two more species Ruminococcus schinkii and Lactovum miscens were present atpeak hydrogen production.The externally seeding strategy could enhance the hydrogen production from sweet potato with peakcumulative H2 production potential (HP) of 120 mmol H2/L-reactor using sewage sludge. However, thecow dung seed showed more ethanol production than hydrogen with peak concentration of12,146 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 <1.19 mm using sewage sludge. The HPRmax, HY and HP
values were affected slightly by the variations in sweet potato particle size. The peak total energy
production yield of 1625 J/g sweet potato was obtained with sweet potato concentration of 150 g/L at pH
8.5 using sewage sludge.
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