Low pH (6, 5, and 4) sulfate reduction during the acidification of sucrose under thermophilic (55°C) conditions

S.I.C. Lopes, I. Sulistyawati, M.I. Capela, P.N.L. Lens

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The effect of a low pH (6, 5 and 4) and different COD/SO42¿ ratios (9 and 3.5) on thermophilic (55 °C) sulfate reduction and acidification of sucrose was investigated using three upflow anaerobic sludge bed reactors fed with sucrose at an organic loading rate of 3.5 gCOD (lreactor d)¿1. The three reactors showed nearly 100% acidification of sucrose for all pH values and COD/SO42¿ ratios investigated. Sulfate reduction was complete at pH 6 and a COD/SO42¿ ratio of 9. At pH 5, sulfate reduction efficiencies were 80¿95% for both COD/SO42¿ ratios (9 and 3.5). At pH 4, sulfate reduction efficiencies further dropped to 55¿65% at a COD/SO42¿ ratio of 9 and 30¿40% at a COD/SO42¿ ratio of 3.5. The pH decrease from 6 to 5 or 4 caused a shift in the acidification products from mainly acetate to butyrate, as well as a higher production of ethanol, especially at pH 4. At pH 4, propionate and methane were not formed and hydrogen concentrations in the biogas reached 50%, equivalent to a hydrogen yield of 1.3 mol H2 (mol glucose)¿1. This study shows that sulfate reduction is possible in the acidification phase of anaerobic wastewater treatment at pH values as low as 6 till 4 and that the pH strongly affects both the acidification pathways and the sulfate reduction efficiencies.
Original languageEnglish
Pages (from-to)580-591
JournalProcess Biochemistry
Issue number4
Publication statusPublished - 2007


  • propionic-acid accumulation
  • granular sludge reactors
  • anaerobic-digestion processes
  • reducing bacteria
  • waste-water
  • acidogenic phase
  • hydrogen-production
  • sulfide toxicity
  • methanol degradation
  • growth


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