Microaerophilic organisms were monitored in sewage effluent undergoing two secondary treatments: air and oxygen-activated sludge. The mean numbers of Arcobacter cryaerophilus and thermophilic campylobacters detected in incoming sewage were 5639/100 ml and 1720/100 ml respectively.
Secondary treatment in air tanks reduced the population of A. cryaerophilus by 97.1% and of thermophilic campylobacters by 99.08%, whereas treatment in oxygen tanks reduced the bacteria 97.8% and 99.63% respectively, showing that oxygen-activated sludge treatment was more effective. Subsequent tertiary treatment with 2 p.p.m. chlorine dioxide evidenced the removal of A. cryaerophilus to 99.9% and eliminated thermophilic campylobacters.
Campylobacter jejuni and C. coli constituted 54.1% and 45.9% of 74 thermophilic campylobacter strains isolated. In air-activated sludge effluent C. jejuni was found more often, thus appearing more sensitive to oxygen.
The most probable number assay used for detection of campylobacters, blood medium for enrichment and blood-free medium for plating, also appeared to be fit for A. cryaerophilus, the high density of which in urban sewage may be due to inflows from slaughterhouses.