A note on the removal of fecal bacteria in cattle slurry after different farm and laboratory treatments

Abstract

We investigated the variations in the numbers of the main groups of indicators of fecal contamination (fecal coliforms, fecal streptococci, and sulfite-reducing clostridia) during various treatments to which cattle slurry was subjected on a farm and in an anaerobic digester in the laboratory. The results indicated that: anaerobic digestion at 35°C for 20 days in a farm, plug-flow, digester produced a reduction (−1 or 2 log 10 ) in the coliform and streptococcus numbers and an increase in the sulfite-reducing clostridia. When the same materials were also subjected to batch anaerobic digestion at ambient temperatures, a drastic reduction (−4 log 10 ) was noted in the numbers of fecal coliforms, a smaller decrease (−3 log 10 ) in the fecal streptococci, but only a slight variation in the clostridial spores; batch anaerobic digestion at 35°C for 50 days produced a reduction (−2 log 10 ) in the fecal coliforms and fecal streptococci, and a slight variation in clostridial spores. After 18 days' digestion at 65°C the fecal coliforms could no longer be found, whereas slight increases were observed in the numbers of fecal streptococci and sulfite-reducing clostridia.