Effects of additives on shifting phosphorus to solid phase during Solid-Liquid separation of digestate in full-scale biogas plant

• Published in: Bioresource technology 2025-01, Vol.416, p.131804, Article 131804
• Main Authors: Sai Tejaswi Uppuluri, Naga, Ran, Xueling, Müller, Joachim, Guo, Jianbin, Oechsner, Hans
• Format: Article
• Language: English
• Subjects: Biofuels; Kieserite; Non-labile-P; Nutrient recovery; Phosphorus; Screw press; Straw flour
• ISSN: 0960-8524; 1873-2976; 1873-2976
• DOI: 10.1016/j.biortech.2024.131804

[Display omitted] •Effect of additives in shifting total phosphorus to solid phase was investigated.•Kieserite and straw flour were used in treating digestate for 4 h and 22 h.•Kieserite treatment for 22 h shifted nearly 67.41 % of total P to solid phase.•Non-labile P fractions increased to 55.29 % with kieserite treatment for 22 h.•Additive treatment before separation effectively shifts total P to solid phase. Phosphorus (P) is critical for plant growth, but global reserves are exhausting within 250–300 years, therefore enhancing phosphate recycling is crucial for the future. Biogas digestate, rich with nutrients is a promising resource for nutrient recovery. Conventional solid–liquid separation shifts approximately 35 % of the total P in the digestate to the solid phase. Separation trials with additive treatment using a screw press with a 0.75 mm sieve were performed at University of Hohenheim’s full-scale biogas plant. After 22 h, 67.41 % (kieserite treatment) and 52.35 % (strawflour treatment) of total P shifted to the solid phase. Treatment with kieserite enhanced P shift into the solid phase by forming non-labile fractions through a chemical bond between P and Mg2+ ions. Kieserite treatment for 22 h effectively increases the share of total P in the separated solid phase, it also ensures a sustainable nutrient supply and mitigates the risk of nutrient runoff.