Waste to Energy: Anaerobic Co-Digestion of Microalgal Biomass and Bakery Waste

Małgorzata Hawrot-Paw () and Jacek Tapczewski
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Małgorzata Hawrot-Paw: Department of Renewable Energy Engineering, West Pomeranian University of Technology in Szczecin, Pawla VI 1, 71-459 Szczecin, Poland
Jacek Tapczewski: Department of Renewable Energy Engineering, West Pomeranian University of Technology in Szczecin, Pawla VI 1, 71-459 Szczecin, Poland

Energies, 2025, vol. 18, issue 20, 1-16

Abstract: Anaerobic digestion is a well-known technology for renewable energy generation. Its efficiency depends on the substrate composition and its biodegradability. Microalgae are considered a promising feedstock due to their rapid growth, high protein and lipid content, and potential for wastewater treatment. However, the mono-digestion is often limited by a low carbon-to-nitrogen (C/N) ratio and a recalcitrant cell wall structure. This study evaluated the potential of co-digesting microalgal biomass with bakery waste under batch conditions. Two types of bakery residues (stale wheat bread and stale wheat rolls), were tested. Each was added to the microalgal biomass at proportions of 25%, 50%, and 75% based on volatile solids (VS). The experiment was carried out in a semi-technical anaerobic digester under mesophilic conditions. During the anaerobic digestion, the biogas volume, gas composition, and the energy potential of the substrates were analysed. The highest biogas yield (494.34 L·kg −1 VS) was obtained from the mixture of microalgae and 75% bread. Although mono-digestion of microalgal biomass resulted in the highest methane concentration, the differences compared to co-digested samples were not significant. The lowest hydrogen sulphide concentration (234.20 ppm) was measured in the 25% rolls variant, while the control sample (100% microalgae) showed the highest H 2 S levels. From an energy perspective, the most beneficial result was obtained with the addition of 75% bread.

Keywords: microalgal biomass; bakery waste; anaerobic digestion; biogas (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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