title: Trade-off between mesophilic and thermophilic denitrification: rates vs. sludge production, settleability and stability.
abstract: The development of thermophilic nitrogen removal strategies will facilitate sustainable biological treatment of warm nitrogenous wastewaters. Thermophilic denitrification was extensively compared to mesophilic denitrification for the first time in this study. Two sequential batch reactors (SBR) at 34 °C and 55 °C were inoculated with mesophilic activated sludge (26 °C), fed with synthetic influent in a first phase. Subsequently, the carbon source was switched from acetate to molasses, whereas in a third phase, the nitrate source was fertilizer industry wastewater. The denitrifying sludge maintained its activity at 55 °C, resulting in an immediate process start-up, obtaining nitrogen removal rates higher than 500 mg N g(-1) VSS d(-1) in less than one week. Although the mesophilic SBR showed twice as high specific nitrogen removal rates, the maximum thermophilic denitrifying activity in this study was nearly 10 times higher than the activities reported thus far. The thermophilic SBR moreover had a 73% lower sludge volume index, a 45% lower sludge production and a higher resilience towards a change in carbon source compared with the mesophilic SBR. The higher resilience was potentially related to a higher microbial diversity and evenness of the thermophilic community at the end of the synthetic feeding period. The thermophilic microbial community showed a higher similarity over the different feeding periods implying a more stable community. Overall, this study showed the capability of mesophilic denitrifiers to maintain their activity after a large temperature increase. Existing mesophilic process systems with cooling for the treatment of warm wastewaters could thus efficiently be converted to thermophilic systems with low sludge production and good settling properties.
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: Emilie N P
authors.initials: EN
authors.lastname: Courtens
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: Siegfried E
authors.initials: SE
authors.lastname: Vlaeminck
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: Ramiro
authors.initials: R
authors.lastname: Vilchez-Vargas
authors.affiliation: The Particle and Interfacial Technology Group (PaInT), Ghent University, Coupure Links 653, 9000 Gent, Belgium.
authors.forename: Arne
authors.initials: A
authors.lastname: Verliefde
authors.affiliation: Microbial Interactions and Processes Research Group, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Ruy
authors.initials: R
authors.lastname: Jauregui
authors.affiliation: Microbial Interactions and Processes Research Group, Helmholtz Centre for Infection Research, Braunschweig, Germany.
authors.forename: Dietmar H
authors.initials: DH
authors.lastname: Pieper
authors.affiliation: Laboratory of Microbial Ecology and Technology (LabMET), Ghent University, Coupure Links 653, 9000 Gent, Belgium. Electronic address: Nico.Boon@UGent.be.
authors.forename: Nico
authors.initials: N
authors.lastname: Boon
mesh_terms: D019149:Bioreactors; D058440:Denitrification; D009584:Nitrogen / Q000378:metabolism*; D012722:Sewage / Q000382:microbiology*; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000382:microbiology
chemical_list: D009584:Nitrogen; D012722:Sewage; D062065:Wastewater
keywords: Biological nitrogen removal; Industrial wastewater; Nitrification; Nitrous oxide; Thermus