Microbial Community Drivers in Anaerobic Granulation at High Salinity

Area of Science:

• Environmental microbiology
• Wastewater treatment engineering
• Anaerobic digestion

Background:

• Anaerobic sludge granulation in upflow anaerobic sludge blanket (UASB) reactors at elevated salinities is understudied.
• The microbial community's role in granule aggregation and stability at high salinity remains unclear.

Purpose of the Study:

• To investigate the microbial community structure and dynamics in granules formed at low and high salinity.
• To elucidate the microbial drivers of granule formation and stability in UASB reactors.
• To assess the impact of substrate composition on granulation at high salinity.

Main Methods:

• Four UASB reactors were operated with synthetic wastewater at low (5 g/L Na+) and high (20 g/L Na+) salinity.
• 16S rRNA gene analysis was used to identify microbial community members.
• Fluorescence in situ hybridization (FISH) and Scanning Electron Microscopy (SEM) were employed to visualize microbial structures and aggregation.

Main Results:

• Acetotrophic Methanosaeta harundinacea dominated methanogens at both salinities.
• Bacterial communities differed: Streptoccoccus at low salinity and Defluviitaleaceae at high salinity.
• Methanosaeta aggregation and bacterial filaments (Streptoccoccus, Defluviitaleaceae) drove granulation.
• Granule formation at high salinity failed when complex protein (tryptone) was replaced by single amino acids.
• This failure correlated with decreased Methanosaeta abundance, lack of clustering, and absence of bacterial filaments.

Conclusions:

• Microbial community structure, particularly bacterial filaments and Methanosaeta aggregation, is key to sludge granulation at high salinity.
• Complex protein substrates are essential for successful granulation in high-salinity UASB reactors.
• The findings highlight the interplay between substrate availability and microbial ecology in wastewater treatment.