Archaeal diversity in biofilm technologies applied to treat urban and industrial wastewater: recent advances and future prospects

Abstract

Biological wastewater treatment (WWT) frequently relies on biofilms for the removal of anthropogenic contaminants. The use of inert carrier materials to support biofilm development is often required, although under certain operating conditions microorganisms yield structures called granules, dense aggregates of self-immobilized cells with the characteristics of biofilms maintained in suspension. Molecular techniques have been successfully applied in recent years to identify the prokaryotic communities inhabiting biofilms in WWT plants. Although methanogenic Archaea are widely acknowledged as key players for the degradation of organic matter in anaerobic bioreactors, other biotechnological functions fulfilled by Archaea are less explored, and research on their significance and potential for WWT is largely needed. In addition, the occurrence of biofilms in WWT plants can sometimes be a source of operational problems. This is the case for membrane bioreactors (MBR), an advanced technology that combines conventional biological treatment with membrane filtration, which is strongly limited by biofouling, defined as the undesirable accumulation of microbial biofilms and other materials on membrane surfaces. The prevalence and spatial distribution of archaeal communities in biofilm-based WWT as well as their role in biofouling are reviewed here, in order to illustrate the significance of this prokaryotic cellular lineage in engineered environments devoted to WWT.

Figure 1

Scanning electron micrographs of anaerobic granular sludge cultivated in an Expanded Granular Sludge Bed (EGSB) reactor. (A) Morphology of anaerobic granules used (40× magnification); (B,C,D) Inner structure of anaerobic granules (6000× magnification). Reprinted from [23], Process Biochemistry, Vol. 40, Wang, J. and Kang, J., The characteristics of anaerobic ammonium oxidation (ANAMMOX) by granular sludge from an EGSB reactor, Pages 1973–1978, Copyright (2005), with permission from Elsevier.

Figure 2

Anaerobic granule formation, according to the model of McHugh et al. [50].