In the present paper work is reported which was carried out at the Technical University Hamburg-Harburg (TUHH) in connection with the retrofitting project of the sewage sludge incinerator of the city of Ulm. In order to keep the emission limits under a variety of operating conditions different primary measures of emission control were examined at TUHH's pilot-scale bubbling fluidized bed combustor (150 mm diameter, height of combustion chamber 9m). In the first phase of the investigations it was shown that the emissions of the pollutants CO and NOx measured at the test rig compare well with those measured at the existing large-scale combustor if operating conditions were chosen according to similarity rules. The main part of the work consisted then of a systematic investigation of the various means to influence the combustion process and the pollutants generating and reducing reactions inside the combustion chamber. In particular, the influences of predrying of the sludge, excess air ratio, staging of the combustion air and flue gas recirculation were investigated. Furthermore, the influence of a mixing element in the freeboard on the emissions was examined. The results which are described in detail in the paper have given valuable advice for the design of the new incinerator. The knowledge of the various influences and interdepences will furthermore allow the operator to choose suitable measures to minimize the emissions and keep the regulation limits under all possible operating conditions.