Project Summary

Hoyle Tanner completed the preliminary engineering study to upgrade the South Woodstock WWTF. The original WWTF was a 50,000 gpd package conventional activated sludge facility that had not been upgraded since 1966. Redundancy was not provided for process tankage including the aeration basin and secondary clarifier. Therefore, the process units could not be taken offline for tank inspection or repair. The facility is now required to nitrify and denitrify with an effluent Total Nitrogen (TN) limit in the NPDES permit. Additionally, a portion of the WWTF site is in the Regulatory Floodway, creating significant limitations on siting new process tankage.
 
For the upgrade of the WWTF, three process alternatives were considered: Sequencing Batch Reactor (SBR), Membrane Bioreactor (MBR), and submerged attached growth bioreactor (SAGB). The alternatives were evaluated based on a life-cycle cost analysis and non-monetary factors. The recommended alternative was an SBR process with an innovative equipment layout, allowing all process equipment to be accessed from above the water line. This allowed for a two-tank SBR process without pre-equalization to meet the Vermont DEC SBR design guidelines. This innovative approach saved capital cost while realizing a lower life-cycle cost, as well. The new facility was constructed and put into service prior to decommissioning the original facility. Construction of the new SBR facility was completed in 2023.