Das Projekt "Understanding and tailoring aerobic granular sludge wastewater treatment systems" wird vom Umweltbundesamt gefördert und von Ecole Polytechnique Fédérale Lausanne, Laboratoire de Biotechnologie Environnementale (EPFL LBE) durchgeführt. Aerobic granular sludge-based systems have been recently proposed as a promising innovative alternative for wastewater treatment. Aerobic granular sludge may be developed in bubble column-type reactors operated in a sequencing batch mode with anaerobic and aerobic phases. The advantages are relatively low operating and maintenance costs and a high density biomass sludge blanket which results in a compact and efficient treatment system. For a successful operation of this promising treatment system, formation of physically and metabolically stable granular sludge is a prerequisite. A detailed understanding of the granule formation, the bacterial populations involved, and the physical structure is still missing and therefore we investigate three main objectives: (i) the competition and relative importance of PAO and GAO in granular sludge structure, (ii) granule formation and stability for optimized nitrogen and phosphorus removal, and (iii) the microbial assembly and community in relation to granular structure. A combination of process engineering approaches with the molecular characterization of the microbial communities of the granules is applied. The results of the first two project years showed that with propionate as substrate a more stable biological phosphorous removal by PAO could be achieved than with acetate. Microbial community characterization showed that it was indeed dominated by PAO in the propionate reactor whereas GAO were predominant when phosphorous removal was low in the acetate reactor. A new methodology to measure PAO activity in real time inside the reactor based on conductivity measurement was developed and will now be applied to study the competition between PAO and GAO in aerobic granular sludge. Different aeration strategies for improving nitrogen removal were also successfully tested leading to increased biological nitrogen removal. Furthermore, a detailed characterization of granule structure showed that they are composed of multiple micro-granules containing one population and that they resemble rather a cauliflower than an onion with several layers. This increased understanding of the granular sludge formation, activity and structure will allow tailoring aerobic granules with desired physical and metabolic characteristics which is required for a robust implementation and reliable operation of this novel system for the treatment of different kinds of wastewaters from municipalities or industry.