Besides the quality of the treated wastewater, secondary objectives dealing with the sustainability of wastewater treatment are gaining importance. This has resulted in several important innovations over the last 20 years, such as granular sludge reactor technologies and innovative nitrogen removal techniques based on anaerobic ammonium oxidation (anammox). In granular sludge reactors, biomass is grown in the form of dense, fast-settling granules, resulting in compact wastewater treatment systems which allow a high loading rate. The anammox conversion comprises the conversion of ammonium and nitrite to nitrogen gas by autotrophic, slow growing micro-organisms. Nitrogen removal techniques based on this conversion result in substantial savings in aeration costs and external carbon source addition costs compared to conventional nitrification-denitrification over nitrate, at the same time minimizing CO2 emission and sludge production. Recently, anaerobic methane oxidizing bacteria (anMOB) have been discovered and first attempts have shown that a combination of anMOB anammox bacteria for a simultaneous nitrogen and methane removal from wastewater is possible. For future process scale-up, research on process engineering is the next key issue. The goal of the proposed research project concerns the optimization in terms of design and control of a granular sludge reactor for simultaneous anaerobic methane and nitrogen removal, to combine the advantages of anammox-based granular sludge reactors with the removal of methane, a strong greenhouse gas. The project involves two stages, in which the application of anaerobic methane oxidizing bacteria is subsequently studied under anoxic and aerobic reactor conditions. The project goal will be achieved combining mathematical modelling and numerical simulation with an experimental approach based on lab-scale reactors.