First study providing data on the reduction of Cl. botulinum during biogas processes


This study aimed to assess the sanitary situation in agricultural biogas plants (BP) regarding pathogenic Clostridium spp.


Methods and Results

The incidence of Clostridium botulinum, Clostridium difficile, Clostridium novyi, Clostridium haemolyticum, Clostridium septicum and Clostridium chauvoei was investigated in 154 plant and animal substrates, digester sludges and digestates from full-scale BP using a method combining microbial enrichment with Real-Time PCR. The investigated clostridia were absent in the samples, except for Cl. novyi that was barely present (3·9%) and Cl. difficile that was more frequently detected (44·8%). Clostridium botulinum exposed to lab-scale digesters in sentinel chambers was reduced with D-values of 34·6 ± 11·2 days at 38°C and 1·0 ± 0·2 days at 55°C.



These findings indicate minor relevance of clostridial pathogens in  BP and an improved sanitary quality of the digestion product compared to untreated substrates concerning Cl. botulinum. However, the frequent detection of Cl. difficile opens questions on the durability of this organism in manure digestion lines.


Significance and Impact of the Study

This is the first study providing data on the reduction of Cl. botulinum during biogas processes that scientifically invalidate contrary claims by some media in the public. Furthermore, the results improve the fragmentary knowledge on the prevalence of several clostridial pathogens in agricultural biogas production.


From Fate of Clostridium botulinum and incidence of pathogenic clostridia in biogas processes


Biogas: potential health hazards for human and animals?

“There are quite strong concern that pathogens can be spread on fields and meadows through the biogas production and the subsequent deployment of biogas residual mass. A gene transfer, ie an exchange of information of the bacteria to each other, during the fermentation process can not be excluded (...) Why shrinks the biogas industry to publish critical and especially thought-provoking studies? You have something to hide? (...) In digestate of biogas plants prevail partially unknown or uncontrollable conditions, which have a significant impact on the microbiome (...) It is time to create clarity by research (...) Ernst-Gunther Hellwig, founder and director of the Academy, calls for an unprejudiced cooperation between all scientists concerned to control residual risks for the benefit of human and animal health. Until the major issues and theories are not scientifically clear and reproducible, no biogas residual mass on fields and meadows should be applied, which are intended for the production of animal feed, or products for human nutrition.”  By Deutschland Agrar und Veterinar Akademie (AVA)