Résumé
Aim: To determine the minimal conditions (temperaturetime), necessary to achieve set sanitation targets for selected microbial indicators during the continuous thermal treatment of pig slurry.
Methods and Results: The effectiveness of thermal treatment between 55 and 96 degrees C was studied using Escherichia coli, enterococci, sulfite-reducing Clostridia (SRC), mesophilic culturable bacteria (MCB), F+-specific and somatic phages. Identification of SRC and MCB was performed using 16S rRNA gene analysis. Ten minutes at 70 degrees C or 1 h at 60 degrees C was sufficient to reduce the vegetative bacteria by 4-5 log(10), but it had little effect on somatic phages nor on spore formers, dominated by Clostridium sp. At 96 degrees C, somatic phages were still detected, but there was a reduction of 3 1 log10 for SRC and of 1 4 log10 for MCB. At 96 degrees C, Clostridium botulinum was identified among the thermotolerant MCB.
Conclusion: Only those hygienic risks relating to mesophilic vegetative bacteria can be totally eliminated from pig slurry treated at 60 degrees C (60 min) or 70 degrees C (<10 min).
Significance and Impact of the Study: Hygiene standards based on the removal of the indicators E. coli and enterococci can easily be met by treatment as low as 60 degrees C (enabling, a low-cost treatment using heat recovery). However, even at 96 degrees C, certain pathogens may persist.