From mechanical biological treatment to anaerobic digestion-challenges in changing plant operations

Abstract

This paper presents the findings acquired in a study on the rearrangement of wet fermendation conditons in an anaerobic digestion (AD) process. As required by the federal law the rural districts “Elbe-Elster” and “Oberspreewald” (AEV) implemented a separate collection system for the organic fraction of municipal solid waste (oFMSW). Accordingly, the input material in AD of the mechanical biological treatment plant in Freienhufen (operated by AEV) is going to be separately collected oFMSW instead of residual waste. The plant operator intends to reduce the investment costs. Thus, the experiment has to refer to the existing plant regime. In order to facilitate the rearrangement on the operating process, the following objectives were investigated: (1) boosting AD by reducing the particle size; (2) recirculating process water to max-imum extent to reduce waste water treatment costs; (3) describing the properties of oFMSW in the course of the seasons. Different variations in pre-treatment, AD and recirculation of process water were tested at lab-scale to the best possible course of action for the implementation in real life. The results show, that reducing the particle size has a minor impact; both on degradation efficiency and biogas production. A major impact on AD can be observed for the varying composition of oFMSW in the course of the seasons. Additionally, the recirculation of process water affects the efficiency of the AD by influencing the volumetric load. However, the recirculation ratio is limited by the ammonia concentration, since it might have an inhibiting effect on the microorganisms’.