Improvements for Excellent Treatment Performance for Years to Come

Blue Plains Advanced Wastewater Treatment Plant is the largest plant of its kind in the world. After several decades of operation, the gravity thickener and primary sludge screening and degritting equipment were at the end of their original design life. 

The Gravity Thickener Upgrades Phase II project improved the solid process operation and reliability of the downstream thermal hydrolysis system at the Blue Plains Advanced WWTP. Originally hired in 2011, we designed upgrades to the mechanical, electrical, instrumentation, and structural components and systems within the primary sludge screening and degritting building, GT Nos. 1–10; gravity thickener control building; GT flow distribution structure; and limited modifications within the solids process building. In addition, modifications were made to the GT influent hydraulic profile to avoid cascading flow conditions between process units to reduce the amount of air entrainment, which reduced the amount of foam and scum occurring on the surface of the gravity thickeners.

In addition to the upgrades, the design team worked collaboratively with DC Water to develop a suggested construction sequence based on allowable shutdown restrictions. Further, the team evaluated different options for construction access and developed an approach to maintain access for DC Water to the adjoining Tunnel Dewatering Pump Station. This information was integrated into the contract documents, and a comprehensive intermediate milestone approach was used to systematically sequence the units for construction — based on specific limitations and allowing for partial beneficial occupancy.

The project overcame challenges by meeting these achievements:

• Advanced a construction sequence that meets allowable shutdowns.
• Developed a construction access plan that maintains access to the TDPS.
• Created an electrical and instrumentation conduit routing approach that allows existing systems to remain operational while new conduit is installed.

The final design was completed in 2018, and a construction notice to proceed was issued in early 2019. After a sequential 4-year construction duration, the project was substantially complete in late 2023.