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Updated: Jul 12, 2026
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Continuously-stirred Anaerobic Digester to Convert Organic Wastes into Biogas: System Setup and Basic Operation
Published on: July 13, 2012
Continuous biogas production from fodder beet silage as sole substrate.
P A Scherer1, S Dobler, S Rohardt
1Research Centre of Environmental Bioengineering and Applied Biotechnology, University of Applied Sciences, Hamburg. Paul.Scherer@rzbd.haw-hamburg.de
Summary
This study shows that 37-45°C is optimal for biogas production from fodder beet silage, maintaining stable reactor performance and efficient recovery after feeding. Higher temperatures, like 65°C, led to process failure due to propionate accumulation.
Area of Science:
- Biotechnology and Bioengineering
- Renewable Energy Sources
- Environmental Science
Background:
- Continuous biogas production from fodder beet silage using a two-step anaerobic digestion plant has been operational since April 2000.
- The plant utilizes two 500 m3 reactors, fed exclusively with silage (pH 3.4-4.1), initially inoculated with swine manure at 37°C.
- Process stability is maintained at pH 7.5-8.0 with a hydraulic retention time (HRT) of approximately 55 days.
Purpose of the Study:
- To investigate the effect of different temperatures on the efficiency and stability of biogas production from fodder beet silage.
- To determine optimal operating conditions, including temperature, organic loading rate (OLR), and hydraulic retention time (HRT).
- To analyze the microbial community structure and volatile fatty acid (VFA) profiles under varying temperature regimes.
Main Methods:
- Four one-step laboratory reactors were operated at 37°C, 45°C, 60°C, and 65°C, fed once daily with silage.
- Organic loading rate (OLR) was set at 3.9 g volatile solids (VS)/(l*d) with an HRT of 27 days.
- Microscopic analyses were performed to examine methanogen morphology; VFA concentrations and gas production were monitored.
Main Results:
- The 65°C reactor ceased gas production after 86 days due to high propionate levels; stable performance was restored at 60°C.
- Temperatures of 37°C and 45°C showed the quickest recovery of gas production, pH, and gas content after impulse feeding.
- Specific gas production rates and methane yields were consistent across tested temperatures (600-700 l biogas/kg VS), with methane content at 62-64%.
Conclusions:
- Optimal temperature for stable and efficient biogas production from fodder beet silage is between 37°C and 45°C.
- Lower temperatures facilitate faster recovery and VFA reduction, favoring methanogenic communities with mixed coccoid and rodlike morphologies.
- Long-term operation with high OLR (12 g VS/(l*d)) and short HRT (7.5 days) is feasible, yielding approximately 40.1 m3 methane/ton fresh silage.
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