Nutrient and trace element supply in anaerobic digestion plants and effect of trace element application.

To investigate process behaviour and process disturbances in anaerobic digestion (AD) plants, samples of more than 1500 main digesters were taken and concentrations of macro- and micronutrients as well as volatile fatty acids were analyzed. Out of these samples, 600 digesters using energy crops only and 80 digesters using waste substrates were selected to compare the chemical composition as a result of different substrate feeding. High variations in element concentrations were found in both groups. In 60 plants with low micronutrient levels, trace elements were added and process changes were observed. A significant decrease of volatile fatty acids and an increase in digester performance were measured after trace element application. Furthermore, an increase of bacterial biomass could be detected.