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Pathogen levels in OWPs

The micro-organisms salmonella and L. monocytogenes were not detected in the OWPs. Helminth eggs and E. coli were detected periodically. Fecal enterococci and C. perfringens are more frequently detected and quantified in the OWPs. All of the distributed OWPs are within the thresholds of applicable standards.

Micro-organisms studied in the OWPs

The micro-organisms sought in the OWPs are those indicated in standards concerning the composts used in farming: NFU 44-095 for agricultural matter of wastewater treatment origin and NFU 44-051, which covers all organic conditioners. These two standards target pathogenic micro-organisms (Listeria monocytogenes, salmonella and helminth eggs) and treatment indicators (Escherichia coli, Clostridium perfringens and enterococci).
The analytical methods used are those recommended by the standards created on the basis of analysis methods in the food industry: NF V08 053 for counting E.coli, NF EN ISO 7899-1 for counting enterocci, XP X 33-017 for finding viable helminth eggs, NF V 08-052 for finding salmonella, NF EN ISO 11290 for finding L. monocytogenes and NF V 08-056 for finding C. perfringens.
Table 1 shows the thresholds for these micro-organisms defined by the standards NF U 44 095 and NF U 44-051. All of the thresholds are mandatory for sludge composts (NF U 44-095). For other composts and organic conditioners, only the thresholds for helminth eggs and salmonella are mandatory. The standard's thresholds for E. coli and enterococci are given for indicative purposes and are not mandatory.

Table 1. Microbiological parameters of the standards NF U 44-051 and NF U 44-095.


Micro-organism levels in OWPs

The OWPs distributed in 2004, 2006 and 2007 were sampled on the day of spreading.

The micro-organisms salmonella and L. monocytogenes were not detected in the composts or manure. Helminth eggs were not detected either, except in the manure spread in 2007. On every occasion, E. coli shows levels below the quantification limit (<100 CFU/g), except in manure in 2004, when it was measured at 16 CFU/g.

The other micro-organisms, fecal enterococci and C. perfringens, were more frequently detected and quantified in the OWPs (see Figures 1 and 2).

The fecal enterococci populations range from 102 MPN (most probable number)/g (BIO, GWS) to 106 MPN/g (RMW). RMW compost and manure show enterococci levels higher than the optional threshold in the standard 44-051 for this micro-organism, which is considered as a treatment indicator. This threshold was also exceeded in 2004 in the BIO compost. Meanwhile, in GWS, the threshold of NF U 44-095 is mandatory but higher (105). The GWS compost spread is within this mandatory threshold.
in manure. This micro-organism is not mentioned in NF U 44-051. However, it is mandatory in NF U 44-095. The GWS compost complied with the standard, with C. perfringens only detected in 2004 at less than 102 CFU/g, which is the threshold of the standard NF U 44-095.
n'ont pas été détectés dans les composts ni dans le fumier.  Les oeufs d'helminthes ne sont pas détectés non plus, excepté dans le fumier épandu en 2007.  E. coli présente à chaque fois des teneurs inférieures à la limite de quantification (<100 UFC/g), excepté dans le fumier en 2004, où elle est mesurée à 16 UFC/g.


Figure 1. Fecal enterococci levels in OWPs from 2004 to 2007 (3 samples for each year).




Figure 2. C. perfringens levels in OWPs from 2004 to 2007 (3 samples for each year).