A two-stage thermophilic-mesophilic anaerobic digestion pilot-plant was operated solely on waste activated sludge (WAS) from a biological nutrient removal (BNR) plant. The first-stage thermophilic reactor (HRT 2 days) was operated at 47, 54 and 60 °C. The second-stage mesophilic digester (HRT 15 days) was held at a constant temperature of 36–37 °C. For comparison with a single-stage mesophilic process, the mesophilic digester was also operated separately with an HRT of 17 days and temperature of 36–37 °C. The results showed a truly thermophilic stage (60 °C) was essential to achieve good WAS degradation. The lower thermophilic temperatures examined did not offer advantages over single-stage mesophilic treatment in terms of COD and VS removal. At a thermophilic temperature of 60 °C, the plant achieved 35% VS reduction, representing a 46% increase compared to the single-stage mesophilic digester. This is a significant level of degradation which could make such a process viable in situations where there is no primary sludge generated. The fate of the biologically stored phosphorus in this BNR sludge was also investigated. Over 80% of the incoming phosphorus remained bound up with the solids and was not released into solution during the WAS digestion. Therefore only a small fraction of phosphorus would be recycled to the main treatment plant with the dewatering stream.
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April 01 2006
Two-stage thermophilic-mesophilic anaerobic digestion of waste activated sludge from a biological nutrient removal plant
S. Watts;
S. Watts
*Advanced Wastewater Management Centre, University of Queensland, Australia
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G. Hamilton;
**Gold Coast Water, Gold Coast City Council, Australia,
E-mail: j.keller@awmc.uq.edu.au
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J. Keller
J. Keller
*Advanced Wastewater Management Centre, University of Queensland, Australia
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Water Sci Technol (2006) 53 (8): 149–157.
Citation
S. Watts, G. Hamilton, J. Keller; Two-stage thermophilic-mesophilic anaerobic digestion of waste activated sludge from a biological nutrient removal plant. Water Sci Technol 1 April 2006; 53 (8): 149–157. doi: https://doi.org/10.2166/wst.2006.245
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