6b

• Biological wastewater treatment reactors

  A 'black box' where the microbial community structure and dynamics are not well understood

  
• Biological wastewater treatment processes

  • Aerobic treatment processes
  • Anaerobic treatment processes

  
• Aerobic treatment processes


  • Activated sludge systems: Carbon removal
  • Nitrification reactors: Ammonia and nitrite removal
• Anaerobic treatment processes


  • High-strength wastewater
  • Treatment sludge
  • Farm waste

  
• Anaerobic treatment reactors


  • Upflow anaerobic sludge bed reactor (UASB)
  • Completely Stirred Tank Reactor (CSTR)
• Probing Activated Sludge with Oligonucleotides Specific for Proteobacteria: Inadequacy of Culture-Dependent Methods for Describing Microbial Community Structure

  
• Bacterial community structures in activated sludge samples from aeration tanks of a two-stage system with a high-load first stage and a low-load second stage were analyzed with oligonucleotide probes

  
• The probes were complementary to conserved regions of the rRNA of the alpha, beta, and gamma subclasses of proteobacteria and of all bacteria

  
• Group-specific cell counts were determined by in situ hybridization with fluorescent probe derivatives
• Contributions of the proteobacterial subclasses to total bacterial rRNA were quantified by dot blot hybridization with digoxigenin-labeled oligonucleotides

  
• The activated sludge samples were dominated by proteobacteria from the alpha, beta, or gamma subclass, accounting for about 80% of all active bacteria found

  
• The culture-dependent community structure analysis of activated sludge produced partial and heavily biased results compared to in situ techniques

  
• Advanced sequencing techniques now allow us to identify microbial communities and their metabolisms in wastewater treatment reactors

  
• Microbial community composition in 13 activated sludge plants from across Denmark (26 samples in total)

  • Characterisation of a core community using 16S rRNA sequencing
  • 63 genera were frequently highly abundant and made up 68% of the organisms observed
  • 252 genera were transient and found in less than 10 samples

  
• Advanced sequencing techniques now allow us to identify microbial communities and their metabolisms in WWTR
• The activated sludge ecosystem contains a core community of abundant organisms

  
• Understanding the microbial ecology of a system requires that the observed population dynamics can be linked to their metabolic functions
• Functional characterization is laborious and the choice of organisms should be prioritized to those that are frequently abundant (core) or transiently abundant, which are therefore putatively make the greatest contribution to carbon turnover in the system
• A core community consisting of abundant OTUs was also observed within the incoming wastewater to three plants
• The net growth rate for individual OTUs was quantified using mass balance, and it was found that 10% of the total reads in the activated sludge were from slow or non-growing OTUs, and that their measured abundance was primarily because of immigration with the wastewater
• Transiently abundant organisms were also identified