Axel Zentner - Institute of Waste Management and Circular Economy, Technische Universität
Christina Dornack - Institute of Waste Management and Circular Economy, Technische Universität

The mechanical biological treatment plant of Freienhufen is used to stabilize residual waste. Since the ruraldistricts Elbe - Elster and Oberspreewald - Lausitz match their waste management with federal law, organicfraction of municipal solid waste (OFMSW) will be collected separately in future. Hence the anaerobicdigestion process has to be converted. The accomplishment has to refer to the existing operating regime toreduce investment costs. This contains a wet fermentation. In order to facilitate the conversion of theoperating process, suitable particle sizes and volumetric loads have to be examined. In addition, the liquidphase of the digestate shall be recirculated maximal to save both fresh water and waste water disposal costs.The one year lasting investigations were performed in lab-scale with a various number of reactors. Beforefeeding the bio-waste was pre-treated. In order to do that, the bio-waste was milled to particle sizes of 2, 4, 8,and 10 mm. In addition, the digestate was dewatered to gain process water. While using the process waterfresh water was substituted in varying proportions. The feeding of the reactors was adjusted to the standardsof the operating plant. For that reason, the dry matter content in the reactor was adjusted at 10.5 %.Depending on the delivered raw material, this restriction led both to unsteady water requirements andvolumetric loading. As a result of investigations an optimal particle size as well as optimal proportion ofrecirculated process water were defined. For that reason, comprehensive analyses were conducted weekly tocharacterize the delivered raw material as well as the solid and liquid phase of the digestate in order todetermine critical moments due to recirculation of process water. In conclusion, liquid and solid phase of thedigestate should be evaluated with regards to application as fertilizer.

Organic Fraction, Solid waste, anaerobic digestion, Wet Fermentation, Process Water, Recirculation