Influence of a water purification unit on the contamination level of salmonella in outcoming water and sludge

Abstract :

Foodborne pathogens occasionally harboured in the gastro-intestinal tract of some domestic animals may be retrieved in slaughterhouses waste water and in sludge of water purification units. Salmonella, pathogen common to man and animals, is often used as a biological risk indicator. The aim of the present study was to assess effectiveness of a recent water purification unit by rapid and semi-quantitative detection of this micro-organism.
The water purification unit collects waste water of seven food-processing industries, including a pig slaughterhouse. This latest was the main source of Salmonella contamination with a level of more 10³ colony forming unit (CFU) per ml, that was very close to the average level of contamination of total incoming waste water. The unit, whose principle of action is based on biological purification, has permitted a 4 log10 reduction of Salmonella contamination, with a final contamination level of less than 1 CFU/ml. It was observed only a little decrease of contamination levels during the biological treatment steps, in contrast with the one observed during the clarification step. This was due to adsorption of bacteria by material in suspension. Fresh sludge were harboured an average of 10² CFU of Salmonella per gram.
In the beginning of December 1999, two sludge piles were let on the ground along a field and sampled microbiologically every month. Seven month later, no Salmonella were recovered from the piles.

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