High salinity in molasses wastewaters shifts anaerobic digestion to carboxylate production

Jo De Vrieze, Marta Coma, Matthias Debeuckelaere, Paul Van der Meeren, Korneel Rabaey

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51 Citations (SciVal)
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Biorefinery wastewaters are often treated by means of anaerobic digestion to produce biogas. Alternatively, these wastewaters can be fermented, leading to the formation of carboxylates. Here, we investigated how lab-scale upflow anaerobic sludge blanket reactors could be shifted to fermentation by changing organic loading rate, hydraulic retention time, pH, and salinity. A strong increase in volatile fatty acid concentration up to 40 g COD L-1 was achieved through increasing salinity above 30 mS cm-1, as well as a decrease in methane production by more than 90%, which could not be obtained by adjusting the other parameters, thus, indicating a clear shift from methane to carboxylate production. Microbial community analysis revealed a shift in bacterial community to lower evenness and richness values, following the increased salinity and VFA concentration during the fermentation process. A selective enrichment of the hydrogenotrophic Methanomicrobiales took place upon the shift to fermentation, despite a severe decrease in methane production. Particle size distribution revealed a strong degranulation of the sludge in the reactor, related to the high salinity, which resulted in a wash-out of the biomass. This research shows that salinity is a key parameter enabling a shift from methane to carboxylate production in a stable fermentation process.

Original languageEnglish
Pages (from-to)293-301
Number of pages9
JournalWater Research
Publication statusPublished - 1 Jul 2016


  • Carboxylate production
  • Fermentation
  • Methane
  • Microbial community
  • Salinity


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