Back River Wastewater Treatment Plant, Egg-Shaped Digesters
Crom Corporation designed and built two 3.0 MG egg-shaped sludge digesters for Baltimore’s Back River Wastewater Treatment Plant. SGH performed a peer review of the structural design of the new digesters. Although egg-shaped digesters are rather common in Europe, they were relatively new to the United States. At the time they were built, the digesters were the largest in the United States.
SGH performed a peer review of the structural design and performed structural analyses of the digesters. The concrete walls of the digesters vary in thickness with elevation and are thickest at the bottom. In addition to mild steel reinforcement, the walls are post-tensioned with high-strength tendons both in the circumferential and vertical directions. The wall terminates at the bottom in a solid concrete cup that is supported on a pile foundation.
Our analyses included calculations for loads due to self-weight, operating contents, thermal gradients, wind, post-tensioning, and loads imposed by the superstructure. We developed a finite element model of the digesters to assist in the analysis. The model consisted of plate bending elements for the wall and solid brick elements for the cup. SGH reviewed the post-tensioning tendon schedule and recommended adjustments that would result in the desired residual compression in the wall of the digester.