Effect of temperature decrease on the microbial population and process performance of a mesophilic anaerobic...

Area of Science:

• Environmental Science
• Biotechnology
• Microbiology

Background:

• Anaerobic digestion (AD) is a key technology for converting crop residues into biogas.
• Temperature significantly influences microbial community structure and function in AD processes.
• Understanding microbial adaptation to mesophilic (33°C) and lower temperatures is crucial for optimizing AD efficiency.

Purpose of the Study:

• To investigate the impact of decreasing temperature on the anaerobic digestion of crop residues.
• To analyze microbial population dynamics during adaptation to lower temperatures.
• To determine optimal temperature ranges for methane production from crop residues.

Main Methods:

• Laboratory-scale continuously stirred fed-batch reactors were operated at 12°C, 18°C, and 33°C.
• Fluorescence in situ hybridization (FISH) was used to monitor microbial community changes.
• Methane production rates and hydrolysis, acidogenesis, and methanogenesis were assessed.

Main Results:

• Stable methane production was achieved at 18°C after microbial adaptation, with yields of 151 ml CH4/g VS added.
• Methane production rates at 25°C (310 ml CH4/l/day) and 37°C (366 ml CH4/l/day) exceeded those at 33°C (215 ml CH4/l/day).
• Hydrolysis decreased below 25°C, with acidogenesis and methanogenesis becoming rate-limiting below 16°C.
• Adaptation to 18°C involved an increase in Bacteria to total prokaryotes ratio and shifts in Archaea populations (increased Methanomicrobiales and Methanosarcinaceae, decreased Methanosaeta).

Conclusions:

• Lowering temperatures to 18°C can enhance methane production from crop residues through microbial adaptation.
• Bacterial enrichment appears to be a key adaptation mechanism for improved AD performance at lower temperatures.
• Temperature management is critical for optimizing anaerobic digestion efficiency and microbial community stability.