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1.
Water Sci Technol ; 75(3-4): 491-500, 2017 02.
Article in English | MEDLINE | ID: mdl-28192343

ABSTRACT

The aim of this work is to compare the capability of two recently proposed two-pathway models for predicting nitrous oxide (N2O) production by ammonia-oxidizing bacteria (AOB) for varying ranges of dissolved oxygen (DO) and nitrite. The first model includes the electron carriers whereas the second model is based on direct coupling of electron donors and acceptors. Simulations are confronted to extensive sets of experiments (43 batches) from different studies with three different microbial systems. Despite their different mathematical structures, both models could well and similarly describe the combined effect of DO and nitrite on N2O production rate and emission factor. The model-predicted contributions for nitrifier denitrification pathway and hydroxylamine pathway also matched well with the available isotopic measurements. Based on sensitivity analysis, calibration procedures are described and discussed for facilitating the future use of those models.


Subject(s)
Ammonia/metabolism , Betaproteobacteria/metabolism , Models, Theoretical , Nitrous Oxide/metabolism , Water Purification/methods , Betaproteobacteria/growth & development , Biomass , Denitrification , Hydroxylamine/chemistry , Nitrites/analysis , Nitrites/metabolism , Nitrous Oxide/analysis , Oxidation-Reduction , Oxygen/analysis , Oxygen/metabolism
2.
Bioprocess Biosyst Eng ; 39(3): 493-510, 2016 Mar.
Article in English | MEDLINE | ID: mdl-26803653

ABSTRACT

Five activated sludge models describing N2O production by ammonium oxidising bacteria (AOB) were compared to four different long-term process data sets. Each model considers one of the two known N2O production pathways by AOB, namely the AOB denitrification pathway and the hydroxylamine oxidation pathway, with specific kinetic expressions. Satisfactory calibration could be obtained in most cases, but none of the models was able to describe all the N2O data obtained in the different systems with a similar parameter set. Variability of the parameters can be related to difficulties related to undescribed local concentration heterogeneities, physiological adaptation of micro-organisms, a microbial population switch, or regulation between multiple AOB pathways. This variability could be due to a dependence of the N2O production pathways on the nitrite (or free nitrous acid-FNA) concentrations and other operational conditions in different systems. This work gives an overview of the potentialities and limits of single AOB pathway models. Indicating in which condition each single pathway model is likely to explain the experimental observations, this work will also facilitate future work on models in which the two main N2O pathways active in AOB are represented together.


Subject(s)
Bacteria/metabolism , Models, Biological , Nitrous Oxide/metabolism , Wastewater/microbiology , Water Microbiology , Water Purification
3.
Bioresour Technol ; 149: 301-9, 2013 Dec.
Article in English | MEDLINE | ID: mdl-24121372

ABSTRACT

Polyhydroxybutyrate (PHB) production directly by waste activated sludge (WAS) was investigated in aerobic fed-batch conditions using acetic acid as substrate. PHB production was induced by phosphorus limitation. WAS of different origin were tested with various degrees of phosphorus limitation and PHB contents of up to 70% (gCOD PHB/gCOD particulate) were obtained. This strategy showed the importance of maintaining cell growth for PHB production in order to increase PHB concentration and that the degree of phosphorus limitation has a direct impact on the quantity of PHB produced. Pyrosequencing of 16S rRNA transcripts showed changes in the active bacteria of the WAS microbial community as well as the acclimation of populations depending on sludge origin. The monitoring of the process appeared as the key factor for optimal PHB production by WAS. Different strategies are discussed and compared in terms of carbon yield and PHB content with the feast and famine selection process.


Subject(s)
Batch Cell Culture Techniques/methods , Butyrates/metabolism , Phosphorus/metabolism , Polyesters/metabolism , Sewage/chemistry , Bacteria/genetics , Bacteria/metabolism , Biological Oxygen Demand Analysis , Feasibility Studies , RNA, Ribosomal, 16S/genetics , Time Factors
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