Occurrence, removal and seasonal variation of "thermophilic" campylobacters in a sewage treatment plant in Italy

Abstract

Monitoring of "thermophilic" campylobacters in a sewage treatment plant in Bologna (Italy) has shown that incoming sewage contained a most probable number of 1630 campylobacters/100 ml. The secondary treatment in activated sludge tanks reduced 98.61% of campylobacters, 95.32% of fecal coliforms, 96.46% of fecal streptococci, 93.36% of salmonellas and 93.01% and 88.29% of BOD5 and COD respectively. Subsequent tertiary treatment with 3 ppm of chlorine dioxide for 15 min reduced 100% of campylobacters and salmonellas. Significant correlation coefficients were found in incoming sewage between campylobacters and salmonellas (p < 0.01) and between campylobacters and fecal coliforms (p < 0.02). Campylobacter jejuni and Campylobacter coli constituted 51.3% and 48.7% respectively of the 80 strains isolated. In incoming sewage 66% of the strains isolated were found to be Campylobacter jejuni whereas Campylobacter coli strains were prevalent in activated sludge effluent (69.7%). The greatest frequency of isolation and the higher counts were obtained during the Spring to Summer period with distinct peaks in May, June and July. This seasonability is probably due to the seasonal variation of campylobacter infections in man and animals.