Bacteriological composition and structure of granular sludge adapted to different substrates.

Area of Science:

• Microbiology
• Environmental Science
• Biotechnology

Background:

• Mesophilic granular methanogenic sludge is crucial for anaerobic digestion processes, particularly in treating industrial wastewater.
• Understanding the bacterial composition and structure of these granules is key to optimizing biogas production and wastewater treatment efficiency.

Purpose of the Study:

• To investigate and compare the bacteriological composition and ultrastructure of anaerobic sludge granules from a full-scale reactor and those adapted to specific substrates (ethanol and propionate).
• To identify the dominant bacterial groups and their spatial organization within different sludge granule types.

Main Methods:

• Utilized immunocytochemical methods and bacterial counting to analyze sludge granule composition.
• Employed light and electron microscopy for ultrastructural examination.
• Applied the most-probable-number (MPN) method and bacterial isolation techniques for detailed characterization.

Main Results:

• Propionate-grown granules exhibited distinct clusters, including rod-shaped bacteria related to Methanothrix soehngenii and a specific spatial arrangement of other bacteria, likely including Methanobrevibacter arboriphilus and a propionate-oxidizer.
• Sludge granules from the industrial reactor and those adapted to ethanol lacked this specific spatial orientation.
• Methanobrevibacter arboriphilus and Methanothrix soehngenii were dominant in propionate-grown sludge, while Methanospirillum hungatei and Methanosarcina barkeri predominated in ethanol-grown granules.

Conclusions:

• Substrate adaptation significantly influences the bacterial composition and spatial organization within anaerobic sludge granules.
• Specific bacterial consortia and structures are associated with efficient propionate degradation in granular sludge.
• The diversity of methanogens varies greatly between granules adapted to different substrates and those from full-scale industrial applications.