T.Z. Osborne Water Reclamation Facility

Originally published in the Summer 2018 issue of NC Currents magazine.

General History
Located in the central portion of the 
state, the City of Greensboro, formerly Greensborough, was named for Major General Nathanel Greene, commander of the American forces at the Battle of Guilford Courthouse in 1781. It is the largest city  in Guilford County and the surrounding Piedmont Triad metropolitan region, with a current population of approximately 277,000. In addition to the manufacture of textiles and tobacco products, Greensboro is a major regional freight rail hub.

The history of water reclamation in Greensboro began with the construction  of the original 4 mgd South Buffalo Creek Treatment Facility in 1928. Over the next 10 years, the North Buffalo Water Recla-mation Facility (WRF) opened to provide secondary treatment for the northern half of Greensboro. By 1984, the South Buffalo Creek Treatment Facility closed and was replaced by the T.Z. Osborne WRF. The North Buffalo WRF was decommissioned in October 2017 and converted into a transfer pump station. All of the wastewater for the City is now treated at the T.Z. Osborne WRF.  

The T.Z. Osborne WRF is a 40 mgd-rated advanced wastewater treatment facility. The plant treats both domestic and industrial wastewater from the City and the surrounding community. In addition, the plant influent consists of approximately 90% domestic and 10% industrial wastewater. The plant operates with an average daily flow of 28 mgd and a peak flow of 100 mgd and the annual operating cost is $11 million. 

The plant’s effluent discharges into 
South Buffalo Creek, which originates in Guilford County. South Buffalo Creek is a major headwater stream in the Cape Fear Watershed and affects downstream drinking water supplies, including Jordan Lake. 

Currently, the City of Greensboro Water Resources Department operates the T.Z. Osborne WRF and sewage collection system that collects and transports sewage to this plant. The collection system is made up of approximately 99,797 connections, 1,629 miles of gravity lines, 49 pump stations, and 88 miles of pressurized sewage force mains.  

Key Treatment Information:

 The current wastewater process is a two-stage activated sludge treatment process, and the primary treatment units consist of:

• Four Huber mechanical bar screens (new)
• Four influent pumps
• Two grit classifiers
• Two flow equalization tanks
• Six primary settling tanks
• 12 aeration basins
• 10 secondary settling tanks
• Three centrifuges
• Six tertiary Aqua Diamond cloth filter basins (new)
• One sodium hypochlorite disinfection system with six contact chambers
• Six cascade aeration
• Two discharge outfall pipeline

SCADA System

 This system consists of multiple computer workstations that utilize GE CIMPLICITY Human Machine Interface (HMI) software. The network communication system incorporates GE programmable logic controllers (PLCs), allowing the staff to monitor and control plant processes from the main control room located in the operations building.

Solids Treatment and Biosolids Management
The T.Z. Osborne WRF incinerates sludge in a fluidized bed incinerator. Before incineration can take place, the sludge 
(which is 96% to 98%) must be de-watered. The first step in this process is to mix a polymer solution with the liquid sludge. The polymer is a flocculant and is used to “charge” the sludge particles, so they will tend to clump, or floc, making it easier to separate the solids from the water. After being treated with the polymer, the sludge is pumped into centrifuges where centrifugal force is used to remove the excess water from the sludge. This drier sludge is referred to as sludge cake. Although the sludge cake is still about 70% water, it is now ready for incineration.

Sludge Incineration
The sludge is burned in a fluidized bed incinerator. This incinerator has one hearth, which is equipped with openings to allow air to be blown through the hearth. The flow of air raises and suspends a layer of sand above the hearth and the sand is heated to approximately 1,400°F. As the sludge is pumped into the incinerator, it comes in contact with the fluidized bed 
of hot sand and results in instantaneous evaporation and then combustion occurs. The same airflow that suspends the sand blows the ash out of the incinerator and into the air scrubbing system where the ash and some of the fine sand is removed. A sand silo provides "make-up" sand and replaces what is removed with the exhaust from the incinerator.

Incinerator Ash Disposal
Water containing ash and sand from the incinerator air scrubbing system is pumped to the ash clarifier. After the ash and sand mixture is allowed to settle in the clarifier, it is pumped to the ash press, where porous fabric belts are used for dewatering. The dewatered ash and sand mixture is hauled to the City’s landfill for disposal.

Personnel 
The T.Z. Osborne staff consists of three sections: operations, maintenance, 
and an industrial waste/lab along with administrative staff. The operations section has 23 full-time employees and two roster employees. The maintenance section has 20 full-time employees and one roster employee. The industrial waste/lab section has eight full-time employees and one roster employee. There are three administrative staff employees and there is a 10-hour work schedule for maintenance, rotating weekends for operations, and flexible work schedules for other staff.

Personnel Development
The staff is provided with the opportunity to work towards all relevant certifications in their field, from biological treatment  to physical/chemical treatment, maintenance technician, pre-treatment, collections and distribution, and lab certifications. In addition, the WaterMARK supervisor training program is provided for all employees.

Safety Program
A divisional Safety Committee exists, and the members participate with the department’s Safety Committee. The department has an incentive program that gives annual leave for participation in safety-related training/committees, along with reporting near misses and helping out with a safe work environment.

Current and Future Expansion 
The T.Z. Osborne WRF is currently under expansion to be upgraded to a 56 mgd biological nutrient reduction wastewater facility. Construction started in 2014 and will continue through 2020. The expansion construction packages are as follows:

Package One - addressed current  and future hydraulic capacity issues  at the North Buffalo WRF. The specific improvements for Package One included conversion of an existing aeration basin at the North Buffalo WRF into a flow equalization basin and adding increased transfer pumping capacity. Improvements at the T.Z. Osborne WRF are necessary to receive the pumped flow from the North Buffalo WRF and include a new flow equalization basin, equalization diversion structure, and flow control/metering vault. The North Buffalo WRF treatment facilities downstream of the influent pump station will be demolished or abandoned. 

Package Two- hydraulically expanded the T.Z. Osborne WRF for treating up to 56 mgd under the current nutrient limits and included improvements to pass the peak future flow with the North Buffalo WRF decommissioned. The improvements for Package Two include new membrane-diffuser grids in the existing aeration basins; two new single-stage blowers; and three new 160-foot diameter clarifiers with associated distribution and return activated sludge pumping, new yard piping for increased flow, and electrical improvements, including a new generator.

Package Three – increased final discharge and filtering capacity to complete hydraulic expansion of the T.Z. Osborne WRF to 56 mgd. The improvements for Package Three include new Aqua Diamond Cloth tertiary filters, two new chlorine contact tanks, modifications to the existing chemical feed facilities, and an additional outfall pipeline. 

Package Four – will add biological nutrient removal (BNR) capacity to 
the plant to meet nutrient removal requirements of the Jordan Lake Rules at the increased capacity of the plant. The improvements for Package Four include construction of six new aeration basins, modifications to the existing aeration basins, including new baffle walls, post-anoxic zone mixing, nitrified recycle, and associated electrical improvements. 
Additional major projects have included the replacement of four existing mechanical bar screens with four new Huber mechanical screens and an additional non-potable water pump station.

After a thorough review of the required BNR processes, the age of the North Buffalo WRF, the costs of the projects, and Greensboro’s unique transfer capabilities, a workgroup of Greensboro Water Reclamation staff and engineering consultants made the decision to close/decommission the North Buffalo WRF and consolidate all wastewater treatment at the T. Z. Osborne WRF. 

The City of Greensboro developed a sequenced closure plan to ensure that 
the North Buffalo WRF site was properly transitioned from an active wastewater treatment facility to a wastewater transfer pumping station. The plan outlined the activities and responsibilities of each section of the Water Reclamation Division and included a master schedule. This plan was very successful and resulted in the decommissioning of the North Buffalo WRF with no major issues. It was a total team effort that made the closure plan successful.
As part of the construction procurement process, Package Three and the Electrical Buildings in Package Four, along with the non-potable pump station, were constructed using the construction-manager-at-risk 
(CMAR) project delivery method. Using 
the CMAR method enabled the City of Greensboro to breakdown construction work packages to small enough sizes to utilize minority, women, and local contractors that would not normally be able to bid or work on this type of specialized work. The City also used mentor/protege relationships to help build capacity and train contractors for future work opportunities. 

For additional information,  please contact:
Elijah Williams, PE – 
Water Reclamation Manager
2350 Huffine Mill Road
Greensboro, NC 27402-3136
(336) 373-4632
elijah.williams@greensboro-nc.gov
www.greensboro-nc.gov