Sludge digestibility and functionally active microorganisms in methanogenic sludge digesters revealed by E. coli-fed...

Area of Science:

• Environmental Microbiology
• Biotechnology
• Waste Management

Background:

• Waste activated sludge (WAS) digestion is crucial for waste treatment and biogas production.
• Efficient digestion relies on diverse, active microbial communities converting sludge components into biogas.
• The digestibility of microbial cells and extracellular polymeric substances (EPS) in WAS, and their associated microorganisms, remains poorly understood.

Purpose of the Study:

• To quantify the digestibility of microbial cells and EPS in WAS.
• To identify the specific microorganisms responsible for sludge component digestion.
• To assess the contribution of different microbial groups to the overall digestion process.

Main Methods:

• Utilized Escherichia coli (E. coli) fed digestion experiments to differentiate microbial cell and EPS digestibility.
• Employed microbial source tracking to identify and quantify functionally active microorganisms.
• Analyzed carbon removal efficiency across different digestion conditions (fresh WAS, thermally pretreated WAS, E. coli, thermally pretreated E. coli).

Main Results:

• Microbial cells demonstrated significantly higher digestibility (69% carbon removal) compared to EPS.
• Releasing organic matter from EPS was identified as a potential rate-limiting step in sludge digestion.
• Key microbial players included fermenters, syntrophic acetogens, and methanogens, with their abundance varying based on substrate.

Conclusions:

• Microbial cells are more readily digestible than EPS in waste activated sludge.
• The composition of the sludge microbiome, particularly the abundance of microbial cell-digesting populations, significantly impacts digestion efficiency.
• Targeting EPS solubilization and enhancing microbial cell digestion are key strategies for optimizing biogas production from WAS.