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Updated: May 27, 2026
11:31
Continuously-stirred Anaerobic Digester to Convert Organic Wastes into Biogas: System Setup and Basic Operation
Published on: July 13, 2012
Methane conversion efficiency as a simple control parameter for an anaerobic digester at high loading rates.
W Charles1, N P Carnaje, R Cord-Ruwisch
1Centre for Organic Waste Management, Murdoch University, South Street, Murdoch, WA 6150, Australia. w.charles@murdoch.edu.au
Summary
Stoichiometric methane conversion efficiency effectively monitors anaerobic digesters. This parameter provides an early warning of digester imbalance, preventing failure during high organic loading rates.
Area of Science:
- Environmental Science
- Biotechnology
- Chemical Engineering
Background:
- Anaerobic digestion is widely used for treating concentrated wastes like industrial effluents and sewage sludge.
- The process is prone to instability, particularly under high organic loading rates, leading to volatile fatty acid (VFA) accumulation and potential digester failure.
- Methane (CH4) production is the desired outcome, but acidification can occur if VFA are produced instead.
Purpose of the Study:
- To investigate anaerobic digester behavior under high loading rates.
- To test the effectiveness of stoichiometric methane conversion efficiency as a control parameter for digester stability.
- To establish critical thresholds for conversion efficiency indicating digester imbalance or failure.
Main Methods:
- Monitoring digester performance, including methane production rate and volatile fatty acid (VFA) accumulation, under varying high loading rates.
- Calculating stoichiometric methane conversion efficiency based on feed rate and gas production.
- Analyzing the correlation between conversion efficiency, loading rate, VFA levels, and hydrogen partial pressure.
Main Results:
- Methane production rate generally increased with the feed rate (loading rate).
- At very high loading rates, methane production became disproportionate to the feed rate increase, leading to VFA accumulation and increased H2 partial pressure.
- Conversion efficiency proved to be a reliable early warning indicator of digester imbalance.
Conclusions:
- Anaerobic digesters remained stable at conversion efficiencies above 75%.
- A drop below 70% conversion efficiency signaled the onset of digester failure.
- On-line monitoring of conversion efficiency, using readily available data, offers an efficient control strategy for maintaining stable anaerobic digestion at high loading rates.
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