A . -M . P O U R C H E R , P . M O R A N D , F . P I C A R D -B O N N A U D , S . B I L L A U D E L , S . M O N P O E H O , M . F E D E R I G H I , V . F E R R É A N D G . M O G U E D E T . 2005.Aims: To study the decrease of enteric micro-organisms including viable nematode eggs, enteroviruses, faecal indicators (Escherichia coli and enterococci) and pathogenic bacteria (Listeria monocytogenes, Salmonella sp. and Clostridium perfringens) of a rural sewage sludge when it is composted for 7 months in mixture with straw. Methods and Results: Numbers of the test organisms and the physico-chemical parameters were measured on a monthly basis on the mixture, on the compost after being turned, and on the pile in three positions representing the part by which air is incoming, the bottom of the pile and the part through which air is outgoing. The lowest temperature in the pile was observed at the bottom, where it did not exceed 50°C against 66°C in the two other areas. There were no significant differences between the three areas in terms of micro-organism survival. Infectious enteroviruses were inactivated rapidly and were not found after the first turning whereas some genomes were detected until after the third turning. Escherichia coli and enterococci presented a similar survival rate and their number decreased by 4 log 10 whereas Salmonella decayed at a greater rate than L. monocytogenes. The numbers of C. perfringens decreased gradually to reach a final concentration in the mature compost of about 10 2 CFU g )1 dry matter (d.m.), which was similar to that of the faecal indicators. Conclusions: The hygienic effect of sludge composting in mixture with straw results in a significant reduction of enteric micro-organisms, the concentration of the faecal indicators in the final product being <64 most probable number g )1 d.m. The concentrations of Salmonella, enteroviruses and viable nematode eggs in the final productwere not detectable which is in accordance with the French legislation. Significance and Impact of the Study: The results which pointed out the different behaviour of the test microorganisms reflect the difficulty to propose a relevant indicator of hygienization. Otherwise, they show that composting is an efficient means for hygienization of sludge of rural wastewater treatment, where the straw is available close to their place of production.

The application of sewage sludge to agricultural land is widely used in France. To determine the impact of sludge treatments, concentrations of Listeria sp., Listeria monocytogenes and faecal indicators were monitored in five types of sludge from three sewage treatment plants in Angers (France) and its suburbs over a 1-year period. On the whole, bacteria were reduced in numbers through sludge treatments. Apart from liming, which leads to reduced levels of bacteria below detection limits, other sludge treatments did not eliminate Listeria sp. and faecal indicators. Listeria sp. and L. monocytogenes were found respectively in 87% and 73% of dewatered sludges and in 96% and 80% of sludges stored in tanks. Concentrations of L. monocytogenes, ranging from 0.15 to 20 MPN g(-1) dry matter in dewatered sludge and from 1 to 240 MPN g(-1) dry matter in sludge stored in tanks, did not show seasonal variations. Spreading of sanitised sludge onto agricultural land results in the addition of 10(6)-10(8) L. monocytogenes per hectare per year, which may contribute to the increase in the dissemination of this pathogenic species in the environment.

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Aims:  This study evaluates the behaviour in spiked sludge of a pathogenic bacteria, Listeria monocytogenes, by cultural and molecular techniques, and compares its survival with the one of a faecal indicator, Enterococcus faecium. Methods and Results:  Listeria monocytogenes strain Scott A and E. faeciumT were followed for 17 days after inoculation in sludge. Kinetics of survival depended on the bacteria and on the technique used [most probable number method, direct plate count or real‐time quantitative PCR (qPCR)]. The concentration of L. monocytogenes decreased rapidly regardless of the technique, but the decrease was much more dramatic with culture techniques than with qPCR. On the contrary, the concentrations of culturable E. faeciumT were stable. Conclusions:  The results suggest that the cells of L. monocytogenes strain Scott A might have entered a viable, but nonculturable (VBNC) status, whereas cells of the indicator bacteria, E. faeciumT, maintained themselves better and stayed culturable. Significance and Impact of the Study:  The difference of survival kinetics in the sludge of a faecal indicator (E. faecium) and a pathogenic bacterium (L. monocytogenes) may be linked to the fact that they either enter or do not enter into a VBNC status.

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