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Updated: Jul 19, 2025

Continuously-stirred Anaerobic Digester to Convert Organic Wastes into Biogas: System Setup and Basic Operation
Published on: July 13, 2012
Digesters as heat storage: Effects of the digester temperature on the process stability, sludge liquor quality, and
Bettina Steiniger1, Christian Hubert1, Christian Schaum1
1Institute of Hydroscience, Chair of Sanitary Engineering and Waste Management, Bundeswehr University Munich, Neubiberg, Germany.
Abstract:
Variation of the digester temperature during the year enables the operation of digesters as seasonal heat storage contributing to a holistic heat management at water resource recovery facilities. Full- and lab-scale process data were conducted to examine the effect of the digester temperature on process stability, sludge liquor quality, and dewaterability. Both full- and lab-scale digesters show a stable anaerobic degradation process with a hydraulic retention time of more than 20 days and organic load rates up to 2.2-kg COD/(m3 ·day) at temperatures between 33 and 53°C. The concentrations of soluble COD and ammonium-nitrogen in the sludge liquor digested at 53°C are 2.6 to 5.8 times and 1.3 times higher, respectively, than in the sludge liquor digested at 37°C. Dewatering tests show an enhancement of the dewaterability but a clear increase in the polymer demand at increased digester temperature. PRACTITIONER POINTS: Digesters can operate as seasonal heat storage within mesophilic and thermophilic temperatures Stable anaerobic degradation process for HRT above 20 days Maintenance of process stability as well as quantity and quality of biogas Increase of soluble COD in sludge liquor at higher temperatures Better dewaterability but higher demand for polymers with increasing temperature.
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