START-UP CHALLENGES IN A SLOW ECONOMY: WHEN LESS THAN DESIGN MINIMUM RULES

摘要

The start-up of the Clark County Water Reclamation District (District) Moapa Valley WaterResource Center (MVWRC) presented several operational challenges. The influent flow andorganic load was significantly less than the design minimum as the project schedule occurredduring an unexpected economic turndown - that continues on today. In order to accelerate startup,the basins were seeded with thickened waste activated sludge from the District’s MainCentral Plant in Las Vegas. Instead of growing and stabilizing, the biomass essentiallydisappeared in a matter of weeks after seeding, resulting in a sharp decrease of the mixed liquorsuspended solids concentration. Start-up troubleshooting indicated that a combination of solidssettling, midge fly larvae invasion, uncontrolled solids wasting, and biofilm formation on tankwalls caused the initial biomass instability. Inconsistent plant performance was also observedduring start-up. Process modeling and field observations indicated that reduced organic load,excessive aeration, and biomass instability were the major causes of the inconsistent processperformance. Process modifications were identified and implemented to address the start-upchallenges experienced by District staff. Supplemental carbon was implemented on anemergency basis. The process configuration and aeration control were modified to minimizeexcessive aeration. The return activated sludge and mixed liquor internal recycle flows wereadjusted to minimize solids settling in the structures. As a result of the start-up optimizationeffort, the MVWRC consistently exceeds both the design treatment goals and the mandatedpermit requirements.