Foam formation in biogas plants caused by anaerobic digestion of sugar beet

The use of sugar beet in anaerobic digestion (AD) during biogas production can lead to process upsets such as excessive foaming in fermenters. In the present study, foam formation in sugar beet-fed digestates was studied in foaming tests. The increasing disintegration grade of sugar beet was observed to have a promoting effect on foaming in the digestate but did not affect the biogas yield. Chemical analysis of foam and digestate from sugar beet silage AD showed high concentrations of pectin, other carbohydrates and N-containing substances in the foam. Both pectin and sucrose showed little foaming in AD. Nevertheless, sucrose and calcium chloride had a promoting effect on foaming for pectin AD. Salts of divalent ions also enhanced the foam intensity in the case of sugar beet silage AD, whereas ammonium chloride and urea had a lessening effect on sugar beet-based foaming.