Utilization of Pistia stratiotes (aquatic weed) for fermentative biohydrogen: Electron-equivalent balance, stoichiometry, and cost estimation

Nonsikelelo Precios Mthethwa, Mahmoud Nasr, Faizal Bux, Sheena Kumari

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7 Citations (Scopus)


This study investigated the utilization of Pistia stratiotes for biohydrogen production via a dark-fermentation process. The aquatic plant was subjected to acid-hydrolysis using H2SO4: 3.0% (v/v) for 40 min, resulting in sugar yield: 122.2 ± 5.2 mg/g. The optimum culture pH was 5.5, achieving hydrogen yield (HY): 2.46 ± 0.14 mol-H2/mol-glucose (3.51 ± 0.20 mg-H2/g-dry weight) at fermentation time 8 h, temperature 25 °C, and substrate-to-biomass (S/X) ratio 1.0 g-COD/g-VSS. The organic mass balance (92–96%) and electron-equivalent balance (92–98%) indicated the reliability of fermentation data. The dominant species included Planctomycetales, Verrucomicrobiales, Clostridiaceae, and Gammaproteobacteria. The phylogenetic analysis confirmed the abundance of hydrogen-producing bacteria such as Bacillus, Clostridium, and Enterobacter. The hydrogenase gene expression provided the highest activity at pH: 5.5 with a cell number 2.53 × 104 copies/ng-DNA compared to pH: 4.5 (6.95 × 103 copies/ng-DNA) and pH: 8.5 (7.77 × 103 copies/ng-DNA). The total cost of the fermentation system including the amortization cost of investment and operating cost was 0.08 $/kg-dry weight (22.8 $/kg-H2 produced).

Original languageEnglish
Pages (from-to)8243-8255
Number of pages13
JournalInternational Journal of Hydrogen Energy
Issue number17
Publication statusPublished - 26 Apr 2018



  • Bacterial community
  • Biohydrogen cost
  • Dark-fermentation
  • Full stoichiometry
  • Pistia stratiotes substrate

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Condensed Matter Physics
  • Energy Engineering and Power Technology

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