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Article

Digested Sludge Quality in Mesophilic, Thermophilic and Temperature-Phased Anaerobic Digestion Systems

1
Department of Water Technology and Environmental Engineering, University of Chemistry and Technology, Technicka, 5, 166 28 Prague, Czech Republic
2
GEMMA—Group of Environmental Engineering and Microbiology, Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya·BarcelonaTech, c/Jordi Girona 1–3, Building D1, 08034 Barcelona, Spain
*
Author to whom correspondence should be addressed.
Academic Editor: Alicia Ronda Gálvez
Water 2021, 13(20), 2839; https://doi.org/10.3390/w13202839
Received: 30 August 2021 / Revised: 28 September 2021 / Accepted: 7 October 2021 / Published: 12 October 2021
Anaerobic digestion (AD) technology is commonly used to treat sewage sludge from activated sludge systems, meanwhile alleviating the energy demand (and costs) for wastewater treatment. Most often, anaerobic digestion is run in single-stage systems under mesophilic conditions, as this temperature regime is considered to be more stable than the thermophilic one. However, it is known that thermophilic conditions are advantageous over mesophilic ones in terms of methane production and digestate hygienisation, while it is unclear which one is better concerning the digestate dewaterability. Temperature-phased anaerobic digestion (TPAD) is a double-stage AD process that combines the above-mentioned temperature regimes, by operating a thermophilic digester followed by a mesophilic one. The aim of this study is to compare the digestate quality of single-stage mesophilic and thermophilic AD and TPAD systems, in terms of the dewaterability, pathogenic safety and lower calorific value (LCV) and, based on the comparison, consider digested sludge final disposal alternatives. The research is conducted in lab-scale reactors treating waste-activated sludge. The dewaterability is tested by two methods, namely, centrifugation and mechanical pressing. The experimental results show that the TPAD system is the most beneficial in terms of organic matter degradation efficiency (32.4% against 27.2 for TAD and 26.0 for MAD), producing a digestate with a high dewaterability (8.1–9.8% worse than for TAD and 6.2–12.0% better than for MAD) and pathogenic safety (coliforms and Escherichia coli were not detected, and Clostridium perfringens were counted up to 4.8–4.9 × 103, when for TAD it was only 1.4–2.5 × 103, and for MAD it was 1.3–1.8 × 104), with the lowest LCV (19.2% against 15.4% and 15.8% under thermophilic and mesophilic conditions, respectively). Regarding the final disposal, the digested sludge after TAD can be applied directly in agriculture; after TPAD, it can be used as a fertilizer only in the case where the fermenter HRT assures the pathogenic safety. The MAD digestate is the best for being used as a fuel preserving a higher portion of organic matter, not transforming into biogas during AD. View Full-Text
Keywords: mesophilic; thermophilic; temperature-phased anaerobic digestion (TPAD); dewaterability; sludge quality; sludge valorisation mesophilic; thermophilic; temperature-phased anaerobic digestion (TPAD); dewaterability; sludge quality; sludge valorisation
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MDPI and ACS Style

Lanko, I.; Hejnic, J.; Říhová-Ambrožová, J.; Ferrer, I.; Jenicek, P. Digested Sludge Quality in Mesophilic, Thermophilic and Temperature-Phased Anaerobic Digestion Systems. Water 2021, 13, 2839. https://doi.org/10.3390/w13202839

AMA Style

Lanko I, Hejnic J, Říhová-Ambrožová J, Ferrer I, Jenicek P. Digested Sludge Quality in Mesophilic, Thermophilic and Temperature-Phased Anaerobic Digestion Systems. Water. 2021; 13(20):2839. https://doi.org/10.3390/w13202839

Chicago/Turabian Style

Lanko, Iryna, Jakub Hejnic, Jana Říhová-Ambrožová, Ivet Ferrer, and Pavel Jenicek. 2021. "Digested Sludge Quality in Mesophilic, Thermophilic and Temperature-Phased Anaerobic Digestion Systems" Water 13, no. 20: 2839. https://doi.org/10.3390/w13202839

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