Slab Creek Wastewater Treatment Plant Improvements

The Slab Creek WWTP Improvements project increases treatment capacity from 3 MGD (average) to 5 MGD (average) and 14 MGD (peak). The major improvements include a new headworks with screening and grit removal systems, retrofitting existing aeration basins with a new biological nutrient removal (BNR) treatment system, PAC and PAA chemical feed systems, PAA contact chamber, RAS/WAS pump station, conversion of existing intermediate clarifiers to aerobic digesters, and solids handling building with screw press equipment, plant water system, and dried sludge storage.

Five different sludge drying technologies were piloted during the design process. Once pilot testing was complete, requests for proposals (RFP) were solicited from sludge drying equipment manufacturers. Boaz was able to pre-select a new system based on a 15-year present-worth analysis of capital, operating, and maintenance costs.

Boaz also solicited proposals from aeration equipment suppliers for biological nutrient removal equipment to convert three existing aeration basins from standard aeration to a BNR treatment scheme. The proposals were also evaluated using a 15-year present-worth analysis and the BNR system was pre-selected.

A major design challenge was to maintain full treatment capability during construction. Two of the existing three aeration basins and final clarifiers were required to be in service at all times during construction. A construction sequence was developed to install the new headworks, RAS/WAS pump station, and associated yard piping in the first phase, then retrofit each of the aeration basins and clarifiers in series. Strategic piping connections and valve placement provide the ability to maintain flow through the existing treatment train (headworks and RAS/WAS pump station). Each set of retrofitted basins can be tested and placed into service with the new treatment train before moving to the next set of basins. The ability to run both new and existing treatment trains simultaneously minimizes the risk of downtime, troubleshooting during startup, and bypass pumping requirements. Construction is underway and is scheduled to complete in January 2024.