According to the German Fertilizer Regulation only sewage sludge that is hygienically safe for human and plant health is still allowed for agricultural use. Similar regulations can also be found in many other countries today.
Pathogens can be inactivated through disinfection (also called hygienisation).
In thermal processes the sludge is heated to a minimum temperature for a minimum period. When liquid sewage sludge is pre-pasteurized (e. g. for 30 minutes at 70 °C) before it is digested, heat is recovered with the use of sludge / sludge-heat exchangers. To prevent clogging of the heat exchangers the sludge must be screened, for example in our Strainpress® Sludgecleaner SP.
Our middle-temperature HUBER Belt Dryer BT achieves that the sewage sludge is not only dried but also disinfected if the sludge is warmer than 70 °C for longer than 30 minutes.
In Solar Dryers continous disinfection is not always possible due to the moderate temperature. The dried sludge is however disinfected if stored in a glasshouse for a year or or when fully dried and kept in summery environmental conditions.