How important are archaea in wastewater treatment plants?

Archaea are not bacteria! While still unicellular, they are as different from bacteria as a they are from you (a Eukaryote). Some cool facts about Archaea:

• First isolated from extreme environments where they compose a larger % of the total biomass. Extreme temperatures, salinity, pressures, and pH – think deep sea vents, highly anaerobic sediments, and acid mine waters.
  
  
• In wastewater, methanogens are archaea. They are found in aerobic digesters, digestive tracts, and deep within wetland soils – oxygen is toxic to these organisms.
  
  
• Ammonia Oxidizing Archaea are responsible for much ammonia oxidation in the ocean. They have a different metabolism than more prevalent wastewater AOB.
  
  

While interesting and common in certain environments, do archaea play a significant role in aerobic wastewater treatment systems? Early attempts to answer this with conventional microbiology resulted in – “we don’t know” as most organisms did not grow on petri dish plates. But using new molecular (DNA) techniques, we can evaluate the percentage of biomass related to archaea vs bacteria.
 
Last week, Paul Campbell used qPCR to test a random sample of four municipal treatment systems (some with upstream anaerobic digesters) and four industrial aerobic treatment systems. Here are the results (% of total biomass)

Note the relatively low levels of archaea in these wastewater treatment systems. Those with higher levels of archaea tended to be those with upstream anaerobic digesters where methanogens are very important. Or systems with longer sludge ages where we also find more niche bacteria in the MLSS. While low in frequency, these archaea may perform some vital functions, but this is not known. We are continuing to use molecular tools to learn more about the wastewater microbial community and will report more of our results as we discover new pathways and interesting organisms.