Cox Creek Wastewater Treatment Upgrade (Md, USA)

Cox Creek Water Reclamation Facility, Anne Arundel County, Maryland

The 15 million gallons per day Cox Creek Water Reclamation Facility (WRF) is the largest wastewater treatment facility in Anne Arundel County and is also the County’s largest single contributor of nitrogen to Chesapeake Bay. The County targeted the enhanced nutrient removal (ENR) upgrade of the Cox Creek WRF as the first step in a plan to upgrade all of their wastewater treatment facilities for ENR.

In consultation with the client, GHD used a two-step approach to select three ENR alternatives for detailed evaluation. During the first step, the ENR Evaluation Matrix Criteria established during a chartering meeting were used to score five general ENR categories.

1. Single-stage activated sludge process
2. Two-stage process
3. Parallel suspended growth systems
4. Single-stage membrane bioreactor (MBR)
5. Three-stage process.

The three categories with the highest score - one, three, and four – were carried forward to the second step of the process. For each category alternative process configurations were developed and scored using the same evaluation matrix. The highest scoring process configuration in each category was selected for the detailed evaluation as follows:

1. Integrated fixed-film activated sludge (IFAS) process retrofit in existing aeration tanks
2. Oxidation ditches in parallel with upgrade of existing biological process
3. MBR retrofit using existing aeration tanks.

For each alternative, calculations were developed for preliminary hydraulics and unit process sizing, summary tables were prepared for design criteria and parameters, process flow diagrams and layouts were developed, and capital and operations cost estimates were compiled.

MBRs were selected as the best solution due to the facility’s very tight site constraints, inadequate existing reactor volume to fully nitrify year round, inadequate existing secondary clarification facilities, limited hydraulic head available for process modifications, and the County’s desire to produce the highest quality effluent possible with the maximum degree of reliability.

The facility is now in the design phase.