In the previous design of digesters, the pre-stressing method of winding wire or mild steel segmental tensioning was mostly used. In the design of four large-scale sludge digesters with an inner diameter of 28 m at Qingdao Haibohe Wastewater Treatment Plant, in order to meet the requirements of corrosion resistance, crack resistance (water and air tightness) and the establishment of high pre-compressive stresses, the first time that the circular prestressing of digesters was used in an unbonded prestressing program.