Overview and prediction of eradication of Salmonella seftenberg W775 During anaerobic Digestion and pasteurization processes

There is a great demand from public authorities at regional, federal and European level for more research on the biosafety of digestates originating from anaerobic digestion. Literature study shows that the current knowledge on thissubject is fragmentary and that biosafety seems to be dependent on the input materials. We aimed to provide policysupporting advice concerning the biosafety of anaerobic digestion and the pre- and post-treatment processes which areused for the processing of a continuously growing variety of agricultural and organic biological waste products. A first objective was to map out the international literature concerning the hygiene of biological processing in regard tohuman and animal pathogens.

Further Authors:
D. Springael - KU Leuven
A. Ceustermans - KU Leuven
A.H. Geeraerd - KU Leuven

The second objective was the mathematical modelling of the evolution of selected andquantifiable indicatororganisms in function of the processing time. This mathematical modelling formed the basis forthe development of a predictive model to evaluate different digestion processes concerning their hygienisation capacity. At first, an extensive literature study was conducted, from which it seems that spore-foming bacteria can survivemesophilic and thermophilic temperatures and a pasteurization step of 1 h at 70°C. Other pathogens will not cause anyproblems on the condition that the retention time is long enough. The retention time and the temperature seem to be themost important parameters concerning the inactivation of these pathogens during biological digestion processes. Theinfluence of other parameters like pH and dry matter content are less investigated.In the next part of our study, the inactivation of pathogens was quantified by mathematical modelling. In this way, it canbe predicted when, for example, a 5 log10 reduction of Salmonella Senftenberg W775 is reached during thermophilicdigestion. This is important as according to the European Regulation (EC) No 1069/2009 other processes might be usedas an alternative for the mandatory pasteurization step to digest category 3 material and/or manure, if they are able toreduce 5 log10 of S. Senftenberg W775 or E. faecalis dependent on the type of waste being digested.It is not easy to characterize the diversity of waste streams on the presence of different pathogens. Moreover, theconstitution of the waste streams, which are digested in a digestion plant, can vary much. Therefore, the emphasis waslaid on the risk analysis of the digestion processes itself. The tool BioSafety@Digestion was developed for use withinMicrosoft® Office Excel®. The tool can be used to determine if a certain digestion process is safe to inactivate certainpathogens. The required data for this, are the temperature of the digester itself and the minimal retention time. The toolis based on the log-lineair microbial inactivation model.As a conclusion, the temperature and the retention time seem to be the most important parameters concerninghygienisation during biological digestion processes. Moreover, mathematical modelling can be used for the predictionof pathogen inactivation and formed the basis for the development of the tool BioSafety@Digestion that indicates which processes are safe to inactivate certain pathogens.

Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 8
Preis inkl. MwSt.: € 8,00
Autor: Dr. Jaak Ryckeboer

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