INACTIVATION OF SALMONELLA-TYPHI BY HIGH-LEVELS OF VOLATILE FATTY-ACIDS DURING ANAEROBIC-DIGESTION

Survival of Salmonella typhi was investigated in an anaerobic digester for cattle dung with volatile fatty acid (VFA) levels of 5000 mg l(-1 ) and pH 6.0. The organism was added to the digester only once in the first experiment and daily in the other. Survival was monitored on alt ernate days. In the single dose experiment, the counts of Salm, typhi declined rapidly and the pathogen was completely eliminated within 12 d in the experimental digester (VFA cn 5000 mg l(-1) and ph 6.0), wher eas 26 d were required in the control digester (VFA ca 100 mg l(-1) an d pH 6.8). T-90 values for the experimental and control digesters were 2.44 d and 4.80 d, respectively. In the daily dose experiment, a four log reduction in the pathogen count was observed in the experimental digester, but only a two log reduction in the control digester at the end of the experimental period, The mean T,, values for the experiment al and the control digester were 4.22 d and 18.63 d, respectively. In both the experiments, statistical analysis of the data showed signific ant differences in the survival pattern of Salm. typhi in the two dige sters.