Projects

Upgrade, Expansion, and Energy Cost Savings: 60-mgd Neuse River WWTP

Rapid residential development in the City of Raleigh brought about the need for the improvement and phased expansion of the Neuse River facility. Improvements included a new equalization basin to handle wet weather flows, facilities for total nitrogen removal, a sludge management plan, and conversion of the existing chlorine contact tanks to ultraviolet disinfection. Hazen and Sawyer was contracted to complete these upgrades and to perform an energy audit to identify efficiency improvements and reduce the facility’s energy costs.

Project Outcomes and Benefits

• 20% annual savings in energy costs as a result of efficiency improvements in treatment process.
• Phased schedule of construction enabled the implementation of improvements within the financial ability of the City.

The Neuse River facility was initially designed as a 30-mgd advanced wastewater treatment plant serving the City of Raleigh. Due to rapid residential development in the City, a program for plant improvement and phased expansion has been needed.

Hazen and Sawyer first performed a comprehensive energy evaluation which showed that the addition of primary treatment facilities and the replacement of existing surface aerators with fine bubble diffused aeration equipment would significantly reduce energy costs.

We then performed design services for the Phase I improvements, involving capacity expansion to 40 mgd, including new grit and scum removal facilities, primary settling tanks and pumping equipment, new waste activated sludge facilities, new flow equalization facilities and flow distribution structures. Phase II improvements included a central control and information room for plant process monitoring and a new aeration system employing fine and coarse bubble diffusers, centrifugal blowers and a computer-based blower/dissolved oxygen control system. The improvements provide an aeration capacity nearly three times that of the existing system and resulted in a 20% annual savings in energy costs.

Subsequently, the City asked Hazen and Sawyer to update the plant’s facilities plan. We conducted cost and economic evaluations and recommended a continued phased expansion program to 60 mgd. Concurrently, a sludge management plan and a study of phosphorus removal technologies were also completed. Biological and chemical phosphorus removal processes were evaluated. Results of the Statewide phosphorus detergent ban made chemical phosphorus removal facilities more economical. The 60-mgd plant expansion included converting the existing chlorine contact tanks to ultraviolet disinfection contactors. The plant’s filtration capacity was increased from 30 mgd to 60 mgd. Several parallel process units and related plant components were added. Total nitrogen removal facilities were also constructed, consisting of partitions within five of the six existing activated sludge basins to create anoxic zones and provide biological nitrogen removal. The project also included methanol storage and feed facilities for possible addition of methanol to the second anoxic zone of the activated sludge basins to enhance the denitrification process and provide capability for effluent total nitrogen concentrations of 3.5 mg/L.