What are Archaea?

  • Archaea are a diverse group of single-cell, microscopic organisms that have no nucleus and other membrane-bound organelles.
  • They have several unique features that different from bacteria. These features include:
    1. enzyme systems that can degrade organic compounds that bacteria cannot degrade including the degradation of wastes produced by bacteria,
    2. higher metabolic rates that provide for more rapid degradation of organic wastes, and
    3. unique structural features that permit the archaea to exist as extremophiles that is, they are able to tolerate extremes in temperature, pH, and salinity.
  • Archaea are able to tolerate and grow in cold and hot temperatures (- 4 to 90oC), low pH (< 3), high pH (> 10), and high salinity (> 10,000 mg/L total dissolved solids). The structural features that contribute to the extremophilic nature of these organisms consist of:
    1. tightly coiled proteinaceous enzyme systems that resist of damage (denaturation) and
    2. chemical bonds in the lipids that make-up the cell membrane that are tolerant of changes in environmental or operational conditions.

Use of Archaea in Wastewater Treatment

  • Archaea are a group of microorganisms that improve wastewater treatment plant performance.
  • Perhaps the best-known archaea that degrade carbonaceous wastes are the methanogens or methane-producing organisms in anaerobic digesters.
  • Archaea are found in soil, fecal waste, wetlands, and surface water, and enter treatment processes through fecal waste and inflow and infiltration (I/I). Unfortunately, the relatively small population size of archaea in the biomass does not permit the organisms to significantly influence treatment performance. Approximately one percent of the biomass consists of archaea. Therefore, archaea as well as bacteria and fungi are added to treatment processes to increase their desired population size in order to improve treatment performance.
  • There are two major archaeal kingdoms, Crenarchaeota and Euarchaeota that have archaea that are capable of performing significant roles in the degradation of organic wastes, if they are present in adequate numbers.
    • Significant archaea in the kingdom Crenarchaeota include thermophilic organisms, acidophilic organisms, and ammonia-oxidizing archaea (AOA).
    • Significant archaea in the kingdom Euarchaeota include halophilic organisms, thermophilic organisms, and methanogens.
  • Archaea perform significant roles in the sulfur cycle. Their novel sulfur-utilizing enzyme systems can oxidize and reduce various forms of sulfur under aerobic and anaerobic conditions. An example of a role that archaea perform in wastewater treatment is the oxidation of sulfide (HS-) to elemental sulfur (S). This oxidation prevents the production of hydrogen sulfide (H2S) and its release to the atmosphere.