---

 

Session- Pathogens: Risks and Regulations

 

---

 

Hygienic Aspects of Composting Biowastes - Legal Situation and Actual Experiences in Germany

 

Reinhard Bohm

 

University of Hohenheim - Institute of Environmental and Veterinary Hygiene, Germany

 

Recycling of organic material containing tissues and wastes of animal origin is connected with the risk of spreading pathogens of man and animals. Moreover the biotechnological process itself may generate bioaerosols and gaseous compounds which may be risky from the point of view of environmental and occupational health protection. Zoonotic agents of bacterial, viral, fungal and parasitic nature can often be found in raw materials as well as under certain epidemiological conditions agents of special veterinary importance as e.g. Food and Mouth Disease Virus too. Since the aerobic thermophilic process of composting is in principle effective in inactivating most pathogens (sporeformers and TSE - agents excluded)criteria have to be set up to ensure the safety of the applied composting process or technology .In German law (Biowaste ordinance) a three step procedure is demanded for this purpose .First only composting procedures shall be applied which have to be validated in a legal fixed procedure. The second step is the steady process supervision by continuous recording of relevant process data and the third step is the regularly supervision of the final product .The test organism chosen for validation of the process itself is Salmonella Senftenberg strain W775 and the parameter chosen for supervision of the final product is the absence of Salmonella in 50 g of material while the amount of samples which have to be investigated depends on the annual output of the plant. The question arises if the chosen organism for process validation and the fixed requirements ( 5 log reduction) will cover the potential microbiological risk from the point of view of human and veterinary hygiene. Recent studies with Food and Mouth Disease Virus, African Swine Fever Virus Classical Swine Fever Virus Pseudorabies Virus Polio Virus and Parvo Virus as well as EHEC - bacteria and Campylobacter are demonstrating ,that the hygienic demands connected with composting source separated biowaste from households are covered by Salmonella Senftenberg W 775. If other wastes representing a higher epidemiological  risk ( e. g. slaughterhouse wastes) are processed by composting, the validation shall be done by Bovine Parvo Virus.

---

 

Strategies for Evaluating the Sanitary Quality of Composting

 

Kasper K CHRISTENSEN, M. Carlsbaek

 

Department of Process and Product Development, SOLUM AS,  Denmark

 

The elimination of pathogens during composting has been the focus of much research, however, little attention has been directed to the strategies for measuring and securing high sanitary quality of compost. Data from a Scandinavian survey initiated to evaluate different strategies for description of the sanitary quality of full-scale composting is presented. The investigation included microbiological analyses of the waste at different stages during the process (spot test analysis) as well as indirect process supervision where physical and chemical parameters were registered. The elimination of pathogens was also investigated by means of a direct process evaluation. In this process, the raw material was inoculated with selected pathogens in bags. After a sanitary composting phase of 2-4 weeks, the bags were collected and analyzed for the survival of the inoculated pathogens. The investigation considered both human and animal pathogens as well as plant pathogens. The use of dry matter, organic matter, C:N ratio, and pH as indicators of the sanitary quality of composting was very difficult. In contrast, the temperature was important for the elimination of pathogens and 70 degree C was necessary for the inactivation of the very heat resistant plant pathogen, tobacco mosaic virus. However, since it was difficult to guarantee uniform temperatures throughout composting systems by temperature measurements alone, it was concluded to be important to supplement with direct measurements of indicator organisms. The direct process evaluation was a valuable tool for identifying parameters for process optimization in different decomposition zones and for detecting pathogens not normally present in the waste. However, it was an unreliable method for evaluating the overall sanitary process, since it was difficult to adequately represent a heterogeneous environment when inoculating a limited number of zones. In contrast, the spot test analysis was a much more accurate method for the analysis of the sanitary process. In addition, it is much simpler and cheaper to perform than direct process evaluation, which makes the spot test analysis very cost-effective.

---

 

Characterisation of Separate Collected Biowaste to Stabilise the Process of Biological Treatment

 

KRAFT,ECKHARD and Bidlingmaier, Werner

 

Bauhaus-Universität Weimar, Germany, Abfallwirtschaft, Germany

 

Legal regulation and standards of quality have established strong requirements on the process stability of biological treatment of biowaste. In addition to these requirements the treatment has to follow economic aspects. According to this constellation the compliance of the quality criteria degree of rotting process is difficult. The characterisation of biowaste and there influence on the fluid flow in packed beds of biowaste has been searched. For the first time a lot of compared experiments to detect the particle density have been done. The particle density can be used to estimate the amount of pores in the biowaste. Particle size distributions have been created from the organic material. Possibilities to specify characteristic classification numbers and effective particle diameters in order to estimate the behaviour of the material have been tested. A test station for determining the water capacity of fresh organic waste has been created. The results will be introduced. The influence of the results of physical characterisation to the aeration, current properties, biodegradation and adsorption processes will be shown. The illustration will be done by showing the impact to mathematical calculated friction of pumped air through the material. For critical operations of biological treatment and according to the stabilisation of the process practical directives could be concluded by the done research.