Metabolic Profiles and Genetic Diversity of Denitrifying Communities in Activated Sludge after Addition of Methanol or Ethanol

Abstract

External carbon sources can enhance denitrification rates and thus improve nitrogen removal in wastewater treatment plants. The effects of adding methanol and ethanol on the genetic and metabolic diversity of denitrifying communities in activated sludge were compared using a pilot-scale plant with two parallel lines. A full-scale plant receiving the same municipal wastewater, but without external carbon source addition, was the reference. Metabolic profiles obtained from potential denitrification rates with 10 electron donors showed that the denitrifying communities altered their preferences for certain compounds after supplementation with methanol or ethanol and that methanol had the greater impact. Clone libraries of nirK and nirS genes, encoding the two different nitrite reductases in denitrifiers, revealed that methanol also increased the diversity of denitrifiers of the nirS type, which indicates that denitrifiers favored by methanol were on the rise in the community. This suggests that there might be a niche differentiation between nirS and nirK genotypes during activated sludge processes. The composition of nirS genotypes also varied greatly among all samples, whereas the nirK communities were more stable. The latter was confirmed by denaturing gradient gel electrophoresis of nirK communities on all sampling occasions. Our results support earlier hypotheses that the compositions of denitrifier communities change during predenitrification processes when external carbon sources are added, although no severe effect could be observed from an operational point of view.Considerable efforts have been made to improve the technology for efficient and economic removal of nitrogen by denitrification in municipal activated sludge. Denitrification is an anaerobic microbial respiration process with a stepwise reduction of nitrate or nitrite via nitric oxide to nitrous oxide or dinitrogen. In the ideal activated sludge process, bacteria denitrify by using carbon compounds in the influent wastewater as electron donors. As a means to improve control strategies for nitrogen removal, external carbon compounds can be added to enhance denitrification rates (10,14,18,19,34,35). Higher rates allow reductions in the hydraulic retention time in the anoxic zones, making it possible to minimize basin volumes (23). For this purpose, methanol and ethanol are most commonly used in practice, although acetate has been reported to give the highest rates in most cases (12,24,(28)(29)(30).Although much is known about process performance after the addition of external carbon sources, little effort has been made to explain the specific effects on the denitrifying communities in activated sludge. The selective pressure from the carbon compound added might affect the composition of the denitrifying community, which would influence metabolic diversity and functional properties of the denitrifiers. For example, it was shown that acetate as the major carbon source in a laboratory-scale reactor selected for denitrifiers with nonflocculating proper...

Activity and Community Composition of Denitrifying Bacteria in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-Using Solid-phase Denitrification Processes

“…60 mg NO3 − -N g −1 [dry wt] h −1 ) under steady-state conditions. These rates are much higher than those recorded for activated sludge with various soluble substrates 13) . However, the SPD reactor-derived washed sludge showed approximately one-third lower denitrification rates with fresh PHBV as the substrate than did the reactors themselves.…”

“…In the present study, therefore, nirS and nosZ genes, encoding cytochrome cd1 nitrite reductase and nitrous oxide reductase, respectively 45) , were used as molecular markers to assess the community composition of denitrifying bacteria in the PHBV-SPD process. These denitrifying-enzyme genes as well as the Cu-containing nitrite reductase gene, nirK, have been used for the molecular characterization of denitrifying microbial communities in different environments including wastewater treatment systems 2,13,32,44,45) . In addition, the predominant culturable denitrifying bacteria from PHBV-SPD reactors were isolated, phylogenetically identified, and studied in terms of their substrate specificity.…”

Denitrification of groundwater using a sulfur-oxidizing autotrophic denitrifying anaerobic fluidized-bed MBR: performance and bacterial community structure

“…Some culture-independent molecular ecology techniques such as fluorescence in situ hybridization, denaturing gradient gel electrophoresis, genetic libraries, and quantitative realtime polymerase chain reaction (PCR) have been applied in a number of studies concerned with the heterotrophic denitrifying communities in wastewater treatment systems (Throbäk et al 2004;Hallin et al 2006;Warneke et al 2011). In addition, barcoded pyrosequencing method was recently used for analyzing bacterial community structural changes of these key denitrifying genes (Mao et al 2011;Zhao et al 2011).…”

Conventional Media Filtration with Biological Activities

“…Furthermore, microorganisms fed with different carbon sources showed distinct features. A report demonstrated that the metabolic profiles obtained from potential denitrification rates with 10 electron donors were altered with their preferences for certain compounds after supplementing methanol or ethanol, and that methanol had the greater impact (Hallin et al 2006).…”