[Microbial Structure of an Enhanced Two-phase High-solid Anaerobic Digestion System Treating Sludge]

Area of Science:

• Environmental Science
• Microbiology
• Biotechnology

Background:

• High-solid anaerobic digestion (HSAD) presents advantages in sludge treatment, including reduced reactor size and energy use.
• Despite benefits, the microbial mechanisms underlying HSAD, particularly in two-phase systems, remain underexplored.

Purpose of the Study:

• To investigate the microbial community structure in a pilot-scale, enhanced two-phase HSAD system treating waste activated sludge.
• To elucidate the microbial mechanisms driving volatile solids removal and methane production in the distinct hyperthermophilic and thermophilic phases.

Main Methods:

• Utilized 16S rRNA clone library technology to analyze microbial communities at steady state.
• Employed an enhanced two-phase anaerobic digestion process: hyperthermophilic acidogenesis (70°C) followed by thermophilic methanogenesis (55°C).
• Processed waste activated sludge with approximately 9% solid content.

Main Results:

• Achieved a 35.7% volatile solid (VS) removal rate and a methane yield of 0.648 m³·kg⁻¹ VS removed.
• Observed significant differences in bacterial composition between the two phases: proteolytic bacteria in the acidogenesis phase and polysaccharide/fatty acid degraders in the methanogenesis phase.
• Identified *Methanothermobacter* as the dominant archaeal genus in both phases, comprising 100% of archaea in the methanogenesis phase.

Conclusions:

• The microbial community structure is distinct between the hyperthermophilic acidogenesis and thermophilic methanogenesis phases in this HSAD system.
• *Methanothermobacter* dominance suggests hydrogenotrophic methanogenesis is the primary pathway for methane formation.
• HSAD systems can be effectively characterized by understanding the specialized microbial consortia in each digestion phase.