Foam formation during anaerobic digestion of sugar beet silage: causes and countermeasures

On-demand electricity generation from biogas can be achieved through variable feeding regimes using easily degradable substrates, such as sugar beet. However, such substrates pose a high risk of foam formation in anaerobic digesters. This study aimed to identify foam-causing compounds in anaerobic digestion of sugar beet silage and to evaluate effective countermeasures. Pectin was identified as primary contributor to foaming during anaerobic digestion of sugar beet silage, while saponins had no effect. Pectinase pre-treatment of sugar beet silage reduced foaming by 30%. Furthermore, the antifoaming effect of seven vegetable oils was compared. Sunflower oil showed the highest foam suppression efficacy, while soybean oil had almost no effect. The acid number of vegetable oils, reflecting the content of free fatty acids, correlated most strongly with their antifoaming performance. These findings show practical strategies for effective foam control during anaerobic digestion of sugar beet silage, enabling flexible feeding for on-demand biogas production.