Even Bacteria are “Down and Out” in a Tough Economy

The start-up of the Clark County Water Reclamation District (District) Moapa Valley Water Resources Center (MVWRC) presented several operational challenges. The influent flow and organic load was significantly less than the design minimum, and the project schedule occurred during the unexpected economic turndown. Based on the construction start-up schedule, there was minimal time for promoting biomass accumulation, so plant operations staff chose to import biomass from a larger plant to seed the MVWRC aeration basins. Instead of thriving and stabilizing, the biomass essentially disappeared in a matter of weeks after seeding. Start-up troubleshooting indicated that a combination of mixed liquor settling, proliferation of midge fly larvae, solids wasting during start-up, and thick biofilm formation on tank walls caused the initial biomass instability. The biomass instability, a reduced organic load, and excessive aeration during start-up lead to inconsistent plant performance. Process modeling confirmed the impact of reduced organic load and excessive aeration on the system. Process modifications were identified and implemented to address the start-up challenges experienced by District staff. The MVWRC is currently exceeding the design treatment goals and consistently meeting permit requirements