EU no 1774/2002; experiences with process validation of biowaste composting & digestion in the Netherlands

Direct process evaluation makes it possible to study the reduction of selected microbes/pathogens separately by using inoculated probes or bags, but the reduction conditions in the probes/bags are not always the same as in the surrounding material in the process.

The Netherlands implemented source separation of municipal garden and kitchen waste by law in 1994, resulting in 1,5 million tons each year. This is processed in 23 facilities. These plants can be classified, using 5 technologies; Bühler/GECO, Tunnel, VAR, PACOM, Biocel. All systems have extensive temperature measurements and quality systems. Regulation (EC) No 208/2006 allows process validation to comply with Regulation (EC) No 1774/2002. This study is focussing on three microbiological requirements: 1. a 5log10 reduction for Enterococcus Faecalis 2. Enterococcus or E.Coli < 1000 cfu/g after sanitation, 3.compost: Salmonella not detected in 25 g. Two validation systems were discussed, spot test analysis and direct process evaluation. We decided to use the spot test analysis which can produce information about requirements 1, 2 and 3 and is cheaper. Enterococcus Faecalis is estimated as Enteroccocus, which is a wider group but the same as mentioned in requirement 2. Direct process evaluation can use specific microbiological strains such as E. Faecalis and viruses and seems to show higher reduction levels (about 2log10 higher) but conditions in the probes can differ from surrounding biowaste in the real process.
 
Three studies using spot test analysis were carried out in 2006:
First: A pilot study in week 7 and 12 (winter), covering the 5 systems used in The Netherlands, covering biowaste from ± 100 municipalities. In all the untreated biowaste the same level of E.Coli and Enterococcus was found (6,2 log units/gr). This is somewhat low for demonstrating a 5log10 reduction. 67% of the samples after sanitation or from fresh compost could meet the standards for E.Coli and Enterococcus (<1000 cfu/g). In plant number 10 (VAR) a 5log10 reduction for Enterococcus was demonstrated. To reduce the risk of recontamination during the sampling, the sampling strategy was simplified.
Second: A study, covering 21 Dutch facilities was carried out in week 22, 25 and 32 (summer). Now the level of Enterococcus in the untreated biowaste was a bit higher although not significant, for all facilities between 6,6 and 7,7 (mean value 7,1 log units/g). This confirms that all Dutch biowaste has the same level of Enterococcus. Over all, the 21 plants demonstrated a 4,7 log units reduction for Enterococcus (7,1􀃆2,4). 15 of the 21 plants showed a reduction of almost 5 log units or more. There was no clear coherence between the used technology (system) and reduction levels. 4 of the 5 technologies were represented in the group of 6 with < 5 log units reduction. Plant number 10 (the best performer in the pilot with > 5 log units reduction) was now in this group of 6. On the other hand, a poor performing facility number 6 (a tunnel system) in the pilot was in this second study one of the best performers. Over all results from 21 plants show lowest Enterococcus values after sanitation before screening (67% of the samples < 1000 cfu/g). Values of Enterococcus in fresh compost are over all higher and inconsistent, indicating regrowth. Results for E.Coli are significant better (after sanitation 76% and in fresh compost 81% < 1000 cfu/g). In all plants (except 1) Salmonella was not detected in the compost.
Third: In addition, at facility number 12 (lowest performer in study 2) a study was carried out with the aim to clarify the inconsistencies in Enterococcus values. When sampling at the right spot during sanitation, 5log10 reduction was demonstrated at this plant. Although temperatures during the first and second stage were > 65 oC, even 3-6 days 75-80 oC, Enterococcus was demonstrated on these temperature levels ranging from 1,40 to 3,11 log units/g. The compost, both 1 and 14 days after screening, showed levels ranging from 5,6 to 6,7 log units/g. We assume regrowth and recontamination both take place because of remoistening the compost with leachate. Evaluation of the sampling strategy and cooled transport to the laboratory proved that the used practice in the studies 1 and 2 was solid.
 
Discussion: applying spot test analysis we showed over all satisfying sanitation in Dutch facilities. But inconsistencies in results show that the performance of facilities can be different when validation according to spot test analysis is repeated. An additional problem is that Enterococcus was demonstrated to survive ±6 days > 70 oC and there are strong indications for regrowth after sanitation. Results indicate no regrowth for E.Coli.
 
Additional work 2007-2008: based on the gathered experience and making use of the improved sampling strategy, the 9 lowest performers from the second study in 2006 have been evaluated, but also 3 plants which were not in the 1th and 2nd study. Spot test analysis was in most cases repeated 3 times at these plants. Enterococcus, E.Coli and Salmonella were analysed. In all cases (except one) 5log10 reduction of Enterococcus was demonstrated as mean value of the 3 measurements and there was compliance with the microbiological requirements 2 and 3. Salmonella was demonstrated in nearly all incoming Municipal Biowaste.



Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2008 (Oktober 2008)
Seiten: 17
Preis inkl. MwSt.: € 16,50
Autor: Ing. Willem Elsinga

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