Cox Creek Water Reclamation Facility, Anne Arundel County, Maryland USA

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GHD was retained by Anne Arundel County for the Enhanced Nutrient Removal (ENR) Upgrade of the Cox Creek Water Reclamation Facility (WRF). The 15.0 mgd (56.7 ML/d) Cox Creek WRF is the largest of the County’s seven (7) major wastewater treatment facilities and is also the County’s largest single contributor of nitrogen and phosphorus to the Chesapeake Bay. 

During the facilities planning phase, a comprehensive examination was made of all plant unit processes and hydraulics.  As part of this project, a decision was made to expand the peak day hydraulic capacity of the facility from 30 to 45 mgd (113 to 170 ML/d) to accommodate observed I/I derived peak flows. ENR alternatives were evaluated in a two-step approach with the first step shortlisting to three alternatives and the second step selecting the final recommendation based on conceptual designs and lifecycle cost analysis. A Membrane Bioreactor (MBR) process was selected to replace the existing MLE process. MBRs proved to be the right choice for the Cox Creek WRF due to 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 as high of quality of effluent as possible with the maximum degree of reliability.

Following a Schematic Design phase, the project moved to detailed design for three (3) separate phased construction contracts.

  • Phase 1 includes new primary clarifiers and influent flow measurement
  • Phase 2 includes new fine screening, reactor improvements, membrane tanks, membrane facility, conversion of existing secondary clarifiers to flow equalization, high flow management facilities, new gravity thickener, new scum handling, and new SCADA system
  • Phase 3 includes headworks upgrade, gravity thickener upgrades, disinfection system upgrades, and odor control

The MBR system, when complete, will be tied for the largest capacity ENR-performance MBR in the world.  The MBR system includes eight (8) parallel trains of hollow fiber membranes and has an attached vertical turbine mixed liquor return pump station with 80 mgd capacity. The MBR system follows four (4) two-pass biological reactors configured as a four-stage nutrient removal configuration with 600% nitrate recycle. Methanol will be added for supplemental carbon for denitrification and ferric chloride for chemical phosphorus precipitation. Centrifugal blowers are used for process aeration and turbo blowers for air scour. The three-phase project has an estimated construction cost of almost US $140 million.

A unique feature of the project is the high flow management system. As a result of lifecycle cost analysis, it was determined that the capital and more importantly, the operating cost of the MBR process could be significantly reduced by diverting flows greater than 30 mgd (302 ML/d) to a separate parallel high flow management system.  Initially, flows will be stored in flow equalization tanks (converted secondary clarifiers). When the tanks become filled, a high flow management system will automatically be initiated. The system uses a combination of contact stabalization and ballasted flocculating settling to achieve secondary biological treatment in a compact footprint which can be started up in less than 30 minutes. The process will be one of the first of its kind in the world and meets state regulatory requirements to provide secondary treatment for all sanitary sewer flows.

The project incorporates many sustainable design features, such as a “green roof” on the membrane facility and state-of-the-art stormwater management and quality control facilities. The process control system is specifically configured to minimize energy use at the facility through a combination of optimizing in-service tankage, cycling aeration, turning down VFD-driven equipment, and using diurnal flow and load equalization. Design of the first two phases is complete and construction will be completed in 2015.

Wastewater Treatment & Recycling


Because all wastewaters are different, it is necessary to work with a team that can combine comprehensive knowledge with practical experience in the fields of chemistry, biology, hydraulics, mechanical processes/equipment, instrumentation and control, materials handling and plant layout.

GHD can deliver on all the process components that make up a wastewater treatment plant. We have designed and project managed more than 300 wastewater treatment plants (including major municipal facilities processing 500Ml a day and industrial projects).

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As the world’s population grows and our standards of living improve so does our need to manage the water in our environment. We need to maximise its application for human well-being and minimise impact on the environment. GHD engineers, scientists and planners can provide sustainable, cost-effective and innovative water solutions.  We assist water utilities and others who provide water services to optimise infrastructure and adapt to environmental changes in ways that balance the needs of our communities. And we enable clients to meet compliance, improve profitability and maintain their commitment to sustainability.

GHD continually expands the boundaries by engaging in research, enhancing existing systems and strategies, evaluating new procedures and transferring technology from other industries into the water industry. We work with our clients through all project stages planning, investigation, design, delivery, operation and renewal.

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