Anaerobic treated organic waste : Effects of sanitation regarding to pathogenic clostridia
The utilisation of organic waste in anaerobic digestion to produce biogas and digestate is a meaningful development regarding to the sustainable use of resources. Yet, it opens room for digestate contamination with clostridia that limits the digestate use. Currently, directives and laws are given for sanitation of input material. The aim of this study is to investigate the effectiveness of given sanitation methods relating to elimination of pathogenic clostridia. Due to the fact that clostridia are able to form heat resistant spores, tests were performed to illustrate temperature and duration of sanitation necessary to eliminate spores. The sanitation procedures were executed at a range of temperature from 70 °C to 134 °C in an oil bath under normal atmospheric pressure and with duration from one to ten hours. Tests were conducted with Clostridium perfringens and Clostridium sporogenes. Results confirmed that spores of these pathogenic clostridia survive at temperatures of 70 °C for at least ten hours. The study shows, that only temperatures over 121 °C and long exposure times under atmospheric pressure reduce outgrowth of tested clostridial spores. Standardized and effective sanitation techniques executed under high pressure allready exist. Their application is strictly ordered for sanitation of high risk material, but it will also work for sanitation of organic waste. In conclusion, the prescribed sanitation of organic waste with 70 °C for one hour has to be reviewed, espiecally for batches of organic waste which are expected to have higher contents of clostridia.