Biogas plants have been considered as a source for possible amplification and distribution of pathogenic bacteria capable of causing severe
infections in humans and animals.
Manure and
biogas wastes could be sources for spore-forming bacteria such as Clostridium botulinum. In the present study, 24 liquid
manure and 84
biogas waste samples from dairies where the majority of the cows suffered from chronic
botulism were investigated for the presence of
botulinum neurotoxins (BoNT) and C. botulinum spores. The prevalence of
BoNT/A, B, C, D, and E in
biogas wastes was 16.6, 8.3, 10.7, 7.1, and 10.8 %, respectively, while in
manure, the prevalence was 0.0, 0.0, 0.0, 8.3, and 4.1 %, respectively. After enrichment of samples in reinforced cultural medium, they were tested for C. botulinum
BoNT/A, B, C, D, and E using ELISA (indirect C. botulinum detection). The prevalence of C. botulinum type A, B, C, D, and E samples in
biogas wastes was 20.2, 15.5, 19, 10.7, and 34.8 %, respectively, while the prevalence in liquid
manure was 0.0, 0.0, 0.0, 8.3, and 12.5 %, respectively. In conclusion, the occurrence of BoNT and C. botulinum spores in
biogas waste of diseased animals indicates an increased and underestimated hygienic risk. Application of digestates from
biogas fermentations as
fertilizers could lead to an accumulation of long lifespan spores in the environment and could be a possible health hazard.