It’s Alive: Bringing the Rehabilitated Columbia Metropolitan WWTP Anaerobic Digesters Back to Life

Last Modified: Jan 31, 2019


  • Michael Bullard, Barry Bickerstaff, Meredith Bridwell - Hazen and Sawyer
  • Michael Foisy, David Wiman - City of Columbia
  • David Wagoner - CDM SMITH CW2020

The City of Columbia (SC) operates the 60-MGD Metropolitan Wastewater Treatment Plant (MWWTP) which utilizes primary clarification and advanced secondary treatment to produce a treated effluent suitable for discharge to the Congaree River. In 2013 the City retained Hazen and Sawyer (Hazen) to prepare a residuals management masterplan to develop a long-term residuals management strategy for the treatment facility in light of upcoming regulatory changes that would impact their continuing use of thermal oxidation for residuals management. The result of this master planning effort was a decision to move away from thermal oxidation for residuals management and rehabilitate the anaerobic digestion facilities to achieve Class B stabilization to open the possibility to beneficially utilize stabilized residuals through a bulk land application program.

The City retained Hazen to provide design services for the rehabilitation following the planning effort and design documents were issued and work began on the rehabilitation of the five (5) existing anaerobic digester tanks at the MWWTP. Major work under the project included:

  • Digester cover replacement on three (3) of the five (5) anaerobic digesters
  • Digester cover rehabilitation on two (2) of the five (5) anaerobic digesters
  • Replacement of gas mixing equipment with pumped mixing equipment
  • Replacement of digested sludge transfer pumps
  • Replacement of digested sludge heating recirculation pumps
  • Replacement of combination boiler-heat exchangers units with new heat exchangers with separate hot water generation by water-tube boilers in a new boiler building
  • Replacement of waste gas flare system
  • Installation of new iron sponge for hydrogen sulfide removal and digester gas compression and drying equipment.
  • The project is being constructed in two major phases with the first phase work including the hot water system improvements (boiler and boiler building) and restoration of digestion functionality for three (3) of the digesters (Digesters #3, #4 and #5). The first phase work was sufficiently completed in mid-year 2018 to allow for biological start-up of these digesters while construction activities progress on the second phase of the project (Digesters #1 and #2).

    This presentation will describe the scope of the rehabilitation improvements and the overall project with focus on work associated with preparing the City of Columbia to operate the rehabilitated digester systems and the biological “cold start” of the system. Specifically, the presentation will describe work done to train operators on the fundamentals of anaerobic digestion and anaerobic digester process control in advance of the start-up and early results from the cold start activities as the team has progressively increased loading rates to the digester to build a healthy anaerobic biomass in the system. Lessons learned during the start-up will be shared.

    For more information, please contact the author at

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