SURVIVAL OF PATHOGENIC BACTERIA DURING MESOPHILIC ANAEROBIC-DIGESTIONOF ANIMAL WASTE

The survival of pathogenic bacteria was investigated during the operat ion of a full-scale anaerobic digester which was fed daily and operate d at 28-degrees-C. The digester had a mean hydraulic retention time of 24 d. The viable numbers of Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Listeria monocytogenes and Campylobacter jej uni were reduced during mesophilic anaerobic digestion. Escherichia co li had the smallest mean viable numbers at each stage of the digestion process. Its mean T90 value was 76-9 d. Yersinia enterocolitica was t he least resistant to the anaerobic digester environment; its mean T90 value was 18.2 d. Campylobacter jejuni was the most resistant bacteri um; its mean T90 value was 438.6 d. Regression analysis showed that th ere were no direct relationships between the slurry input and performa nce of the digester and the decline of pathogen numbers during the 140 d experimental period.