Metro Wastewater Reclamation District,
PAR 1085 South Secondary Complex Improvements Project
- Conversion of a 100 mgd high purity oxygen facility to biological nutrient removal.
- Construction of a 240 mgd primary effluent pump station to feed the aeration basins
- Retrofit of 10 secondary clarifiers with maze-type energy dissipating inlet
- Detailed construction sequencing and operational strategies developed to allow continued compliance throughout construction.
Metro Wastewater Reclamation District’s (MWRD) long-term master plan acknowledged more stringent future discharge criteria for nutrients and recommended complete biological nutrient removal (BNR) at the Robert W. Hite Treatment Facility (RWHTF), prompting conversion of the high purity oxygen activated sludge process in the South Secondary Complex to a BNR air activated sludge process, similar to that currently being operated in the North Secondary Complex. In January 2008, Metro selected Carollo to provide $17 million of design services for the South Secondary Improvements Project. The Metro District serves approximately 1.5 million people in a 380-square mile service area.
In order to meet projected discharge limits, it is necessary to provide both nitrification and denitrification capability at the South Secondary Complex. Six new 16.7 mgd aeration basins are designed for a three stage nitrification/denitrification process that can be easily modified to biological phosphorus removal in the future. Three centrate and RAS re-aeration basins (CaRRB) are being constructed to treat the nitrogen-rich centrate from dewatering and increase the volume under aeration to promote the growth of nitrifying organisms. Once the modifications to the South Secondary Complex are complete, centrate can be split equally to the North and South Secondary Complex, balancing the ammonia load at the RWHTF.
This project also includes design of a 240-mgd primary effluent pump station, blower building with five 30,000 scfm single-stage centrifugal blowers, mixed liquor recycle pump stations, RAS/WAS pump stations, chemical feed systems, power feed system, and modification of the existing secondary clarifiers. The construction cost for these improvements is $135 million. Following the expansion of the South Secondary Complex, MWRD will have the capacity to fully nitrify and denitrify peak month flows of over 160 million gallons of wastewater a day.