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Summary The purpose of these studies is to investigate in which way the process of anaerobic fermen- tation at mesophilic (33°C) and thermophilic temperatures (53-55 °C) leads to the inactivation of a number of different bacterias and viruses with epidemic relevance, or their corresponding indicator-organisms. Therefore different substrate-combinations of biodegradable kitchen waste, cattle slurry and leftovers (cattle slurry/leftovers 3: 1; cattle slurry/leftovers/kitchen waste 2:1:1; cattle slurry/citchen waste 1:1) were tested for the influence on inactivation or also stabilization of the indicator-organisms Salmonella Senftenberg, Escherichia coli, Ente- rococcus faecium, Clostridium perfringens, Campylobacter jejuni and bovine Parvovirus dur- ing anaerobic fermentation. Attention was kept especially on the so far only rarely considered germs Clostridium perfrin- gens and Campylobacter jejuni. To answer the underlaying questions, the studies on the indicator organisms were at first ac- complished at semi-technical biogas plants and afterwards at two plants in practice to verify the experimentation results. The studies included Input/Output-Tests as well as tenacity tests, with different carriers (Vol- ume-germ-carriers for bacterias and Sandwich-carriers for viruses). Conclusions ?The chosen carrier-systems are useful for controlling and testing anaerobic Co- fermentation processes. Even in large functioning plants it is possible to install system devices which allow carrying out the experiments as part of a process examination in accordance with the german law BioAbfV (1998) regulations. ? Salmonella Senftenberg should further be maintained as a test-organism. Escherichia coli, Enterococcus faecium had shown more stability in comparison to Salmonella Senftenberg. The bovine Parvovirus is particularly useful as a test-organism, to cover a specific risk that rises from using up critical raw material, such as leftovers or animal residues to approve and validate the plant (BÖHM, 2004). Also HOFERER (2001) in- dicated Enterococcus faecium and bovine Parvovirus as potential indicator-organisms. The use of Clostridium perfringens and/or Campylobacter jejuni does not seem to be so evident. The tenacity of Campylobacter jejuni is covered by Salmonella Senften- berg and Enterococcus faecium. Testing with Clostridium perfringens is only useful to test or validate sterilization procedures for the utilization of category III material (VO EG Nr. 1774/2002). ? To inactivate Salmonella Senftenberg and Campylobacter jejuni safe, the mesophilic fermentation alone is enough. A combination of heat treatment and mesophilic fer- mentation can reduce Enterococcus faecium and Escherichia coli about 6-8 logo units, bovine Parvovirus about 5 logo10 units. No test-combination was able to inactivate Clostridium perfringens safely, not even when temperatures of 90 °C were reached. ? The mesophilic fermentation process, both with pre- and post- heat treatment, can pro- duce hygienically safe products. However, due to the elimination of germs, it is highly recommendable to employ pre-heating, because the following fermentation supports the titer reduction further (LEUZE 1984). ? With thermophilic fermentation, the inactivation of Salmonella Senftenberg, Escher- ichia coli and Campylobacter jejuni is safe after 24 hours. Enterococcus faecium is re- duced about 3 log10 units after 24 hours and after at least 7 days about 7 loglo units. The bovine Parvovirus can be reduced about 3-7 logo units after 24 hours. In the case of Clostridium perfringens, there was no markable difference in the number of germs, compared to the mesophilic fermentation. But surprisingly, the inactivation of Clos- tridium perfringens worked better if the part of biological kitchen waste was higher. D-values decreased significantly. ? The tests in the plants in practice left no doubt, that the process is working in function. Controlling the process by screening of temperature, as continuous as possible and on at least three representative sites of the fermentation substrate, is useful and necessary for plants in practice, as also described in the BioAbfV (1998). ? Over all it can be stated that biotechnological processes show only limited germicide effects. Being epidemically safe in this case means that only the amount of those germs is reduced which have a similar resistance as the tested germs (BREITENFELDT, 1997). ?Under observance of all conditions (fermentation temperature, passing time and con- trol-management) the latest knowledge referring to studies at thermophilic plants and mesophilic plants with a pre-heating unit leads to the conclusion that they can produce at least "hygienically safe" products (PHILIPP et al., 2000).