High salinity in molasses wastewaters shifts anaerobic digestion to carboxylate production.
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.
Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
Jo
J
De Vrieze
Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
Marta
M
Coma
Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
Matthias
M
Debeuckelaere
Department of Applied Analytical and Physical Chemistry, Coupure Links 653, B-9000 Gent, Belgium.
Paul
P
Van der Meeren
Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium; Advanced Water Management Centre, The University of Queensland, Brisbane, Queensland 4072, Australia. Electronic address: Korneel.Rabaey@UGent.be.
Korneel
K
Rabaey
D000693:Anaerobiosis; D019149:Bioreactors / Q000382:microbiology; D008697:Methane / Q000096:biosynthesis; D008965:Molasses; D054712:Salinity; D012722:Sewage / Q000382:microbiology; D062065:Wastewater
D008697:Methane; D012722:Sewage; D062065:Wastewater
Carboxylate production; Fermentation; Methane; Microbial community; Salinity