Growth of Microalgae-Bacteria Flocs for Nutrient Recycling from Digestate and Liquid Slurry and Methane Production by Anaerobic Digestion

• Published in: Applied sciences Vol. 12; no. 15; p. 7634
• Main Authors: Béji, Olfa, Adouani, Nouceiba, Poncin, Souhila, Li, Huai-Zhi
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.08.2022; Multidisciplinary digital publishing institute (MDPI)
• Subjects: Algae; Alternative energy sources; Ammonia; Anaerobic digestion; Aquatic microorganisms; Bacteria; Biogas; Biomass; Carbon dioxide; Chemical and Process Engineering; Chemical oxygen demand; Dilution; Effluents; Engineering Sciences; Environmental Engineering; Environmental Sciences; Experiments; Inoculum; liquid digestate; Liquid manure; liquid slurry; Methane; microalgae-bacteria flocs; Microorganisms; Nutrient removal; Nutrients; nutrients recycling; Pollutant removal; Pollutants; Production capacity; Recycling; Slurries; Substrates; Volatile solids; wastewater treatment; Water treatment; France; United States > US
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app12157634

Biogas production by anaerobic digestion from different wastes represents a growing interest in the panel of renewable energy. Digestate has already been a subject of numerous studies as part of microalgal culturing because it is still rich in nutrients. This study wants to use it as a reference to investigate the possibility to exploit Slurry for the same applications. The first part of this research aims to evaluate microalgae-bacterial flocs growth for nutrient recycling from liquid digestate and slurry, working at three different dilutions (10%, 30%, and 50%) of these two substrates, in order to determine the best value for nutrients and pollutants removal (ammonia and chemical oxygen demand removal rate) and microalgae-bacterial biomass production (autotrophic index). The best dilutions were 30% for digestate and 10% for slurry, allowing the highest ammonia and chemical oxygen demand removal rates. The second part evaluated methane production during anaerobic digestion at different ratios of substrate/inoculum (0.2, 0.5, and 0.8), using microalgae-bacterial flocs as a substrate and digestate or slurry as the inoculum. After 30 days, the anaerobic digestion without flocs showed the best performance compared to digestion with flocs (726.7 mL CH4·g−1 slurry, 245.6 mL CH4·g−1 digestate), whereas, for flocs digestion, the best ratio for both inocula was 0.2 substrate/inoculum with 317.2 mL CH4·g−1 slurry and 165.7 mL CH4·g−1 digestate. All solid masses are expressed in terms of volatile solids (VS).