Utilization of Biomasses from Landscape Conservation Growths Dominated by Common Ragwort (Jacobaea vulgaris Gaertn.) for Biomethanization

Abstract

The highly toxic species common ragwort (Jacobaea vulgaris Gaertn.) prefers to migrate into protected dry grassland biotopes and limits the use of the resulting biomass as animal feed. There is an urgent need for a safe alternative use of the contaminated biomass apart from landfill disposal. We investigated the optional utilization of biomethanization of fresh and ensiled common ragwort biomasses and evaluated their energetic potentials by estimation models based on biochemical characteristics and by standardized batch experiments. The fresh and ensiled substrates yielded 174 L_N∙kg^-1 oDM methane and 185 L_N∙kg^-1 oDM, respectively. Ensiling reduced the toxic pyrrolizidine alkaloid content by 76.6%; a subsequent wet fermentation for an additional reduction is recommended. In comparison with other biomasses from landscape cultivation, ragwort biomass can be ensiled readily but has a limited energy potential if harvested at its peak flowering stage. Considering these properties and limitations, the energetic utilization is a promising option for a sustainable handling of Senecio-contaminated biomasses in landscape conservation practice and represents a safe alternative for reducing pyrrolizidine alkaloid entry into the agri-food sector.

Keywords: Jacobaea vulgaris; PA degradation; Senecio jacobaea; biogas yield; energetic conversion; fermentation characteristics; pyrrolizidine alkaloids; wet co-digestion.

Figure 1

Total ion chromatogram (TIC) of a GC-MS analysis for identification and determination of the relative abundance (RA) of the PA-bouquet of J. vulgaris plant material utilized in this study.

Figure 2

Extent of degradation of the total amount of PAs/PANOs after 92 days of ensiling. Different letters indicate significant differences in PA/PANO content (Dunn-Test, p < 0.001). Error bars represent the standard deviations of the means.

Figure 3

Extent of PA/PANO-degradation during ensiling of our study and comparable studies with PA-containing Senecio species. Results are ordinated according to the dry matter content of their silage substrates and the percentage of the S. vulgaris resp. Senecio biomass in the ensiled feedstock. The main types of the pyrrolizidine alkaloids are color coded (see legend for details).

Figure 4

Specific methane yields of fresh and ensiled biomasses from J. vulgaris. Presented are the means and the corresponding standard deviations as error bars. Dots mark the amount of specific methane yield potential according to Weißbach (2008). For comparison, the yield of the prevalent companion grasses according to Meserszmit et al. (2019) is additionally shown.

Figure 5

Daily methane production (expressed as norm liters per kg volatile matter) throughout the batch trial period of 30 days. Red triangles present the mean methane yield of the respective measurement event. Dots indicate the single results of the three batch vessels that served as replicates.

Figure 6

Volume percentages of the two main biogas components methane (CH₄) and carbon dioxide (CO₂) during the course of the batch wet fermentation period. Dots indicate the measurement results of the individual batch vessels in triplicate. Trendlines were constructed using local regression approaches (loess).

Figure 7

Potential specific methane yields (expressed as norm liters per kg volatile substrate) of common ragwort feedstock harvested at different developmental stages. Different letters inside the bars indicate statistically significant differences between the four stages ranging from BBCH 44 to BBCH 66. Error bars represent standard deviations of the mean.