Following some general explanations regarding the function of sludge digesters as components of sewage treatment systems, the paper deals with a sludge digester system in Bottrop. It consists of four egg-shaped reactors with a useful content of 15 000 m[sup 3]. The plant is designed for daily digestion of 3 000 m[sup 3] and a period of digestion of 20 days. Briefly described are the design blueprints tendered, special proposals regarding the construction of the shells and for the design of the base or foundation, as well as the actual construction work and special static and design features. (LU).