[Survival of Salmonella typhimurium in the solid fraction from a farm waste water treatment plant].

Survival of Salmonella typhimurium pathogens was followed in the slurry solid fraction from a pig farm waste water treatment plant. The tested S. typhimurium pathogens have survived for 117 days. The solid fraction was kept in the laboratory at 20-23 degrees C. Indicatory microorganisms at the beginning of the experiment numbered 10(8)-10(9) CFU in 1 ml sample. This number decreased by 4-5 series throughout the experiment, except for faecal coliform bacteria, which were not detected after 43 days of cultivation. Enterobacteria showed a decreasing tendency until day 83, however, on the final sampling (day 117) their count was almost double. Of physico-chemical parameters, pH showed the most striking variations. Its initial value of 6.9 increased to 8.1 at day 30, then decreased to 7.2 at day 43, and increased to 7.7 at the end of the experiment. Ammoniacal nitrogen in solid fraction was almost twice as high as the initial level. Other physico-chemical parameters were not changed significantly throughout the experiment. On the results of this experiment, decimal reduction times T90 were determined for indicatory microorganisms during the storage of solid fraction under constant conditions: psychrophilic bacteria 31.25; mesophilic bacteria 38.12; coliform bacteria 27.49; faecal streptococci 24.57 and enterobacteria 30.46 days. These data suggest a relatively long time of survival for indicatory microorganisms in the solid fraction from agricultural waste water treatment plants.